Case-parent Triads Research Articles

Growth Hormone Deficiency in Childhood Intracranial Germ Cell Tumor Survivors.

Intracranial germ cell tumor (iGCT) survivors have multiple risk factors for growth hormone (GH) deficiency, a commonly reported late effect in childhood cancer survivors. The objective of this study is to examine the prevalence of GH deficiency among childhood iGCT survivors. Participants were previously enrolled in the Germ Cell Tumor Epidemiology Study (GaMETES), a case parent triad study conducted using the Children's Oncology Group registry protocols, including 216 cases with iGCTs. Data on late effects and outcomes are available for 129 iGCT cases who consented for a follow-up study including a self-administered questionnaire and medical record retrieval. GH deficiency was identified via self-report and validated through medical record review. Chi-squared and Fisher's exact tests were used to examine cases with GH deficiency predating iGCT detection. Logistic regression was used to identify predictors of GH deficiency as a late effect. Of 129 iGCT cases who participated in the late effects study, 45% had GH deficiency; 18% had GH deficiency predating the iGCT and 27% developed GH deficiency within a median of 19 months after diagnosis. Younger age at diagnosis, suprasellar location, and higher radiation doses were associated with GH deficiency as a late effect. GH deficiency is highly prevalent as an early clinical sign for iGCT and frequently arises as an early late effect after treatment. Additional investigation is needed to address earlier detection and treatment for this highly prevalent late effect in iGCT survivors.

GADGETS: a genetic algorithm for detecting epistasis using nuclear families.

Epistasis may play an etiologic role in complex diseases, but research has been hindered because identification of interactions among sets of single nucleotide polymorphisms (SNPs) requires exploration of immense search spaces. Current approaches using nuclear families accommodate at most several hundred candidate SNPs. GADGETS detects epistatic SNP-sets by applying a genetic algorithm to case-parent or case-sibling data. To allow for multiple epistatic sets, island subpopulations of SNP-sets evolve separately under selection for evident joint relevance to disease risk. The software evaluates the identified SNP-sets via permutation testing and provides graphical visualization. GADGETS correctly identified epistatic SNP-sets in realistically simulated case-parent triads with 10 000 candidate SNPs, far more SNPs than competitors can handle, and it outperformed competitors in simulations with many fewer SNPs. Applying GADGETS to family-based oral-clefting data from dbGaP identified SNP-sets with possible epistatic effects on risk. GADGETS is part of the epistasisGA package at https://github.com/mnodzenski/epistasisGA. Supplementary data are available at Bioinformatics online.

Abstract 632: Growth hormone deficiency in childhood germ cell tumor survivors

Abstract Introduction: Germ cell tumors (GCTs) are a rare heterogenous group of cancers accounting for 3% of childhood cancers and 15% of cancers in adolescents. Cure rates for GCTs exceed 90% and GCTs currently comprise the 3rd largest group of childhood cancer survivors in the United States. Little systematic evidence exists on late effects of cancer treatment in this group. Treatment for GCTs includes some combination of chemotherapy, radiation, and gonadectomy; interventions that place survivors at high risk for developing endocrinopathies. One of the most common endocrinopathies experienced by childhood cancer survivors is growth hormone deficiency (GHD). In this analysis, we evaluated the prevalence of growth hormone deficiency among GCT survivors. Methods: Participants were previously enrolled in the Germ Cell Tumor Epidemiology Study (GaMETES), which is a case parent triad study conducted using the Children's Oncology Group registry protocols. Data on late effects and outcomes are currently available for a subset of the participants who have provided additional consent for a follow-up study including a self-administered questionnaire and medical record retrieval. GHD was identified via self-report and validated through medical records. Treatment information was abstracted from the medical records. Results: In this interim analysis, 230 participants completed the self-administered questionnaire, including 61 with ovarian tumors, 40 with testicular tumors, 38 extragonadal tumors, and 92 intracranial tumors. Thirty-six of the participants reported having growth hormone deficiency (GHD), all of whom had intracranial germ cell tumors (iGCTs). Thus, the prevalence of GHD among iGCT survivors was 39.1%. We validated 45 questionnaire responses against chart review of iGCT patients. Among these 45, 24 (53.33%) iGCT survivors had GHD. Participants who were treated with high doses of cranial radiation (>30 Gy) were more likely to have GHD (OR = 2.3, 95% CI 0.4-13.1). Conclusions: Growth hormone deficiency is highly prevalent in survivors of childhood intracranial germ cell tumors. The increased prevalence is likely related to the propensity for germ cell tumor involvement of the pituitary stalk, chemotherapy and cranial radiation. Exposure to higher cumulative doses of cranial radiation is associated with higher risk for developing growth hormone deficiency. Citation Format: Diana W. Lone, Karim T. Sadak, Bradley S. Miller, Aubrey K. Hubbard, Jeannette Sample, Michelle Roesler, Jenny N. Poynter. Growth hormone deficiency in childhood germ cell tumor survivors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 632.

Genetic variations at 10q26 regions near FGFR2 gene and its association with non-syndromic cleft lip with or without cleft palate

ObjectivesIn our study, we focussed on three SNPs in the non-coding regions near FGFR2 gene, as studies on non-coding variants in the genome are the novel trends to identify the susceptible loci for nonsyndromic cleft lip with or without cleft palate (NSCL/P). FGFR2 gene is selected as a candidate gene based on knock out animal models and the role played in syndromic forms of clefting. FGFR2 gene also plays an important role in FGF signaling pathway during craniofacial development. MethodsIn the present study 148 case-parent triads were assessed for three SNPs rs10749408, rs11199874 and rs10788165 near FGFR2 gene by using TaqMan allelic discrimination method. Transmission disequilibrium test (TDT) was used to find the allelic association. Linkage disequilibrium (LD) between the markers was analysed using Haploview program 4.2. Haplotype transmission effects were estimated using FAMHAP package. The possible parent-of-origin effects were assessed by likelihood based approach. ResultsTDT analysis of three SNPs failed to show significant transmission disortion from heterozygous parents to the affected child and are not associated with NSCL/P. Linkage disequilibrium analysis showed strong LD between rs11199874 and rs10788165 SNPs. In the haplotype TDT analysis, GG haplotype of rs11199874-rs10788165 showed significant undertransmission to affected child. No significant parent-of-origin effects were observed. ConclusionThe present study on noncoding variants near FGFR2 gene is not associated with NSCL/P. As the numbers of triads included in the study are less, further studies are needed including large sample size to find association with NSCL/P.

Abstract 1209: The association between the cell cycle control pathway and pediatric germ cell tumors

Abstract Pediatric germ cell tumors (GCTs) account for approximately 6% of childhood cancers. GCTs are heterogeneous but are grouped together due to a common cell of origin, the primordial germ cell. GCTs are predicted to have high heritability, therefore, genetic association studies are paramount in understanding GCT etiology. Genome-wide association (GWA) studies commonly ignore the aggregate effect of SNPs/genes with weaker individual associations. Pathway-based approaches provide the opportunity to interrogate joint SNP effects in pathways of interest. The cell cycle control pathway is a plausible candidate pathway given the knowledge that alterations in the the mitotic-meiotic switch may lead to genetic instability and initiate GCT development. In this analysis we evaluated a set of 94 genes associated with cell cycle control using data from a case-parent triad study of pediatric GCT. Genes involved in cell cycle control were identified using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. We also included additional genes based on reports in the literature suggesting a role in cell cycle control in GCTs, including STRA832, 33, CYP26B134, CKS1B35, and E2F636. Variants within 25,000 base pairs upstream or downstream of the gene were selected for inclusion resulting in a total of 2,846 SNPs included in the analysis. Genotyping data were generated using the Illumina HumanCore Exome Array for 867 GCT cases and their unaffected parents. Preliminary results evaluating individual effects of SNPs in the pathway were conducted using the transmission disequilibrium test (TDT). We did not observe any individual SNP associations that reached genome-wide significance; however, suggestive associations were observed for SNPs located in CDKN2C (p=0.000208), MCM7 (p=0.000787), RB1 (p=0.000798), RBL2 (p=0.00250) and TP53 (p=0.00257). Replication of these findings will be conducted using data from a record linkage case-control study from neonatal biobanks in California and Michigan (N=837 cases and 1057 controls). In addition, we will utilize pathway-based approaches to jointly evaluate the effects of genes in this pathway, including Gene Set Enrichment Analysis for Genome wide association study (i-GSEA4GWAS), MetXcan for functional significance, and Family-based rare-variant association analysis (PedGene). In conclusion, our results suggest that genes within the cell-cycle control pathway play a role in the etiology of pediatric GCT. Citation Format: Aubrey K. Hubbard, Nathan Pankratz, Spencer T. Kelley, John J. Meredith, Jenny N. Poynter. The association between the cell cycle control pathway and pediatric germ cell tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1209.

Gene\u2013methylation interactions: discovering region-wise DNA methylation levels that modify SNP-associated disease risk

BackgroundCurrent technology allows rapid assessment of DNA sequences and methylation levels at a single-site resolution for hundreds of thousands of sites in the human genome, in thousands of individuals simultaneously. This has led to an increase in epigenome-wide association studies (EWAS) of complex traits, particularly those that are poorly explained by previous genome-wide association studies (GWAS). However, the genome and epigenome are intertwined, e.g., DNA methylation is known to affect gene expression through, for example, genomic imprinting. There is thus a need to go beyond single-omics data analyses and develop interaction models that allow a meaningful combination of information from EWAS and GWAS.ResultsWe present two new methods for genetic association analyses that treat offspring DNA methylation levels as environmental exposure. Our approach searches for statistical interactions between SNP alleles and DNA methylation (G ×Me) and between parent-of-origin effects and DNA methylation (PoO ×Me), using case-parent triads or dyads. We use summarized methylation levels over nearby genomic region to ease biological interpretation. The methods were tested on a dataset of parent–offspring dyads, with EWAS data on the offspring. Our results showed that methylation levels around a SNP can significantly alter the estimated relative risk. Moreover, we show how a control dataset can identify false positives.ConclusionsThe new methods, G ×Me and PoO ×Me, integrate DNA methylation in the assessment of genetic relative risks and thus enable a more comprehensive biological interpretation of genome-wide scans. Moreover, our strategy of condensing DNA methylation levels within regions helps overcome specific disadvantages of using sparse chip-based measurements. The methods are implemented in the freely available R package Haplin (https://cran.r-project.org/package=Haplin), enabling fast scans of multi-omics datasets.

Prevalence of childhood growth hormone deficiency in survivors of pediatric intracranial germ cell tumors.

e22526 Background: Survival rates for childhood cancer continue to rise, and there are now greater than 420,000 survivors in the United States. However, high cure rates come at the cost of short and long-term treatment-related toxicities. Endocrine disorders are among the most common late effects and are associated with poor health outcomes and lower quality of life. Survivors of pediatric intracranial germ cell tumors (iGCTs) are at high risk for endocrine disorders, particularly for growth hormone deficiency (GHD), due to their exposures to cranial radiation, chemotherapy, and brain surgery. To date, no long-term follow-up studies have explored the late effects experienced by survivors of iGCTs. Methods: Study participants were enrolled in the Germ Cell Tumor Epidemiology Study, which is a case-parent triad study conducted using the resources of the Children’s Oncology Group’s Childhood Cancer Research Network. Eligibility criteria included diagnosis with a germ cell tumor in any location at age 0-19 years in the years 2008-2015. The study population included 233 cases with a diagnosis of iGCT. We are currently following the cohort to evaluate outcomes and late effects of treatment, including medical record review to extract data on treatment characteristics and hormone deficiencies. This interim analysis includes chart review for 57 iGCT cases. Results: Of the 57 cases reviewed, there was a male predominance (73.7%) with the highest prevalence in non-Hispanic whites (80.4%). Cases of iGCTs can be subdivided into two main histologic subtypes, germinomas (36 cases) and non-germinomatous GCTs (NGGCT, 21 cases). The median age at diagnosis was 14.6 years for the germinomas and 10.5 years for NGGCTs. Data on growth hormone deficiency (GHD) was available for 42 of the 57 cases with a median follow-up of 7.4 years. Twenty-eight of the 42 cases (66.7%) had GHD; 19 in the germinoma group and 9 in the NGGCT group (p = 0.47). 17 of those with GHD were males (p = 0.10). There was no significant difference in prevalence of GHD by age of tumor diagnosis (p = 0.20). Conclusions: Survivors of iGCTs are at high risk for growth hormone deficiency. Identifying specific risk factors for developing GHD amongst these survivors can enhance the current guidelines for screening and management.

A genome-wide association study implicates the BMP7 locus as a risk factor for nonsyndromic metopic craniosynostosis.

Our previous genome-wide association study (GWAS) for sagittal nonsyndromic craniosynostosis (sNCS) provided important insights into the genetics of midline CS. In this study, we performed a GWAS for a second midline NCS, metopic NCS (mNCS), using 215 non-Hispanic white case-parent triads. We identified six variants with genome-wide significance (P ≤ 5 × 10-8): rs781716 (P = 4.71 × 10-9; odds ratio [OR] = 2.44) intronic to SPRY3; rs6127972 (P = 4.41 × 10-8; OR = 2.17) intronic to BMP7; rs62590971 (P = 6.22 × 10-9; OR = 0.34), located ~ 155kb upstream from TGIF2LX; and rs2522623, rs2573826, and rs2754857, all intronic to PCDH11X (P = 1.76 × 10-8, OR = 0.45; P = 3.31 × 10-8, OR = 0.45; P = 1.09 × 10-8, OR = 0.44, respectively). We performed a replication study of these variants using an independent non-Hispanic white sample of 194 unrelated mNCS cases and 333 unaffected controls; only the association for rs6127972 (P = 0.004, OR = 1.45; meta-analysis P = 1.27 × 10-8, OR = 1.74) was replicated. Our meta-analysis examining single nucleotide polymorphisms common to both our mNCS and sNCS studies showed the strongest association for rs6127972 (P = 1.16 × 10-6). Our imputation analysis identified a linkage disequilibrium block encompassing rs6127972, which contained an enhancer overlapping a CTCF transcription factor binding site (chr20:55,798,821-55,798,917) that was significantly hypomethylated in mesenchymal stem cells derived from fused metopic compared to open sutures from the same probands. This study provides additional insights into genetic factors in midline CS.

Design efficiency in genetic association studies.

Selecting the best design for genetic association studies requires careful deliberation; different study designs can be used to scan for different genetic effects, and each design has its own set of strengths and limitations. A variety of family and unrelated control configurations are amenable to genetic association analyses, including the case-control design, case-parent triads, and case-parent triads in combination with unrelated controls or control-parent triads. Ultimately, the goal is to choose the design that achieves the highest statistical power using the lowest cost. For given parameter values and genotyped individuals, designs can be compared directly by computing the power. However, a more informative and general design comparison can be achieved by studying the relative efficiency, defined as the ratio of variances of two different parameter estimators, corresponding to two separate designs. Using log-linear modeling, we derive the relative efficiency from the asymptotic variance of the parameter estimators and relate it to the concept of Pitman efficiency. The relative efficiency takes into account the fact that different designs impose different costs relative to the number of genotyped individuals. We show that while optimal efficiency for analyses of regular autosomal effects is achieved using the standard case-control design, the case-parent triad design without unrelated controls is efficient when searching for parent-of-origin effects. Due to the potential loss of efficiency, maternal genes should generally not be adjusted for in an initial genome-wide association study scan of offspring genes but instead checked post hoc. The relative efficiency calculations are implemented in our R package Haplin.

Genome-wide association analysis of autism identified multiple loci that have been reported as strong signals for neuropsychiatric disorders.

Autism is a common neurodevelopmental disorder with a moderate to a high degree of heritability, but only a few common genetic variants that explain the heritability have been associated. We performed a genome-wide transmission disequilibrium test analysis of a newly genotyped autism case-parent triad samples (127 trios) in Han Chinese, identified top association signals at multiple single nucleotide polymorphisms (SNPs), including rs9839376 (OR = 2.59, P = 1.27 × 10-05 ) at KCNMB2, rs6044680 (OR = 0.319, P = 4.82 × 10-05 ) and rs7274133 (OR = 0.313, P = 3.22 × 10-05 ) at PCSK2, and rs310619 (OR = 2.40, P = 7.44 × 10-05 ) at EEF1A2. Furthermore, a genome-wide combined P-value of individual SNPs in two independent case-parent triad samples (total 402 triads, n = 1,206) identified SNPs at EGFLAM, ZDHHC2, AGBL1, and SNX29 as additional association signals for autism. While none of these signals achieved a genome-wide significance in the two samples of our study, they have been reported in a previous genome-wide association study of neuropsychiatric disorders, and the majority of these SNP have a significant cis-regulatory association with mRNA in human tissues (false discovery rate (FDR) < 0.05). Our study warrants further study or replication with additional sample for association with autism and other neuropsychiatric disorders. Autism Res 2020, 13: 382-396. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Autism is a common neurodevelopmental disorder, heritable, but only a few common genetic variants that explain the heritability have been associated. We conducted a genome-wide association study with two cohorts of autism case-parent triad samples in Han Chinese and identified multiple single nucleotide polymorphisms that were reported as strong association signals in a previous genome-wide association study of other neuropsychiatric disorders or related traits. Our study provides evidence for shared genetic variants among autism and other neuropsychiatric disorders.

Haplin power analysis: a software module for power and sample size calculations in genetic association analyses of family triads and unrelated controls

BackgroundLog-linear and multinomial modeling offer a flexible framework for genetic association analyses of offspring (child), parent-of-origin and maternal effects, based on genotype data from a variety of child-parent configurations. Although the calculation of statistical power or sample size is an important first step in the planning of any scientific study, there is currently a lack of software for genetic power calculations in family-based study designs. Here, we address this shortcoming through new implementations of power calculations in the R package Haplin, which is a flexible and robust software for genetic epidemiological analyses. Power calculations in Haplin can be performed analytically using the asymptotic variance-covariance structure of the parameter estimator, or else by a straightforward simulation approach. Haplin performs power calculations for child, parent-of-origin and maternal effects, as well as for gene-environment interactions. The power can be calculated for both single SNPs and haplotypes, either autosomal or X-linked. Moreover, Haplin enables power calculations for different child-parent configurations, including (but not limited to) case-parent triads, case-mother dyads, and case-parent triads in combination with unrelated control-parent triads.ResultsWe compared the asymptotic power approximations to the power of analysis attained with Haplin. For external validation, the results were further compared to the power of analysis attained by the EMIM software using data simulations from Haplin. Consistency observed between Haplin and EMIM across various genetic scenarios confirms the computational accuracy of the inference methods used in both programs. The results also demonstrate that power calculations in Haplin are applicable to genetic association studies using either log-linear or multinomial modeling approaches.ConclusionsHaplin provides a robust and reliable framework for power calculations in genetic association analyses for a wide range of genetic effects and etiologic scenarios, based on genotype data from a variety of child-parent configurations.

Genetic polymorphisms in MTR are associated with non-syndromic congenital heart disease from a family-based case-control study in the Chinese population

Genetic polymorphisms of folate pathway genes have been reported to be associated with congenital heart diseases (CHDs); however, the results remain conflicting. We conducted a family-based case-control study, which included160 CHD case-parent triads and 208 control-parent triads to explore the association of 18 genetic variants of seven folate metabolism-related genes with the risk of CHDs. The MTR C allele of rs1770449 (OR = 1.961, 95%CI: 1.379–2.788) and the MTR A allele of rs1050993 (OR = 1.994, 95%CI: 1.401–2.839) in infants were associated with an increased risk of CHDs. Over-transmission of SNPs rs1770449 and rs1050993 and haplotype CAA (rs1770449-rs1805087-rs1050993) in MTR were detected in total CHDs. The above mentioned associations of MTR with CHDs were also observed in septal defects and conotruncal heart defects subgroups. Without maternal periconceptional folate intake, the risk of CHDs among women carrying the rs1770449 “CT or CC” genotype or the rs1050993 “AG or AA” genotype in MTR was 3.262(95%CI: 1.656–6.429) or 3.263(95%CI: 1.656–6.429) times greater than the aOR in women carrying wild genotype, respectively. Our study suggests that MTR polymorphisms (rs1770449 and rs1050993) may be associated with the risk of CHDs and modify the relation between maternal folate intake and CHDs.

ULK4 Genetic Variants Have Pleiotropic Effect on Risk of Autism, Associated with Brain mRNA Expression and Antipsychotic Treatment Response

Background: ULK4 genetic variants have been implicated for adult-onset psychiatric disorders, and common variants are associated with hematologic and cardiologic disorders at genome-wide significance. This study aimed to examine the pleiotropic effect of ULK4 on the risk of autism, cis-association with mRNA and impact on antipsychotic treatment response in humans. Methods: The clinical genetic data comprised one cohort of autism case-parent triad sample in the Han Chinese and three cohorts of family-based samples in the European ancestry, from Autism Genetic Research Exchange, the Autism Genome Project and the Simons Foundation for Autism Research Initiative; mRNA expression in postmortem human prefrontal cortex across the lifespan and different brain regions of postmortem human brain and other tissues from two independent datasets were used for examining the cis-association with ULK4 variants. Antipsychotic treatment response data were from the Clinical Antipsychotic Trials in Intervention Effectiveness in patients with chronic schizophrenia. Transmission disequilibrium test was used to examine the genetic association with autism. General linear regression analysis was performed for cis-association with mRNA expression. The Cox proportion hazard model was used to analyze the primary outcome, the time to discontinued use of antipsychotics. Results: Multiple functional SNPs including rs2272007 in strong linkage disequilibrium at ULK4 were associated with autism in the Han Chinese sample (minimum p < 0.00071) which survived the Bonferroni correction for multiple testing. SNP rs2272007 and other SNPs were significantly associated with ULK4 expression in postmortem human prefrontal cortex in subjects across the lifespan and multiple brain areas in two independent datasets. In addition, two SNPs rs7651623 (Hazard Ratio, HR = 16.33; p = 5.00 × 10−4) and rs2030431 (HR = 17.25; p = 3.00 × 10−4) in strong LD were associated with the risk of discontinuing use of antipsychotic medications in the patients with schizophrenia. SNP rs2272007, perfect LD with rs7651623, was associated with treatment response in olanzapine only (HR = 4.22; p = 0.0034). Conclusion: We provide evidence at multiple layers for ULK4 common genetic variants associated with the risk of autism. This may have clinical implication for translational research and precision psychiatry

Association between a common missense variant in LOXL3 gene and the risk of non-syndromic cleft palate.

To investigate possible association between functional common variants in the lysyl oxidase like 3 gene and non-syndromic cleft palate we selected a common missense variant p.Ile615Phe (rs17010021), which was predicted to have a probably damaging effect on the lysyl oxidase like 3 enzyme. We genotyped 258 non-syndromic cleft palate case-parent triads of European origin and tested genetic association using the transmission disequilibrium test and log-linear regression analyses of genotypic relative risks and of parent-of-origin effects. The observed genotype frequency in parents was in Hardy-Weinberg equilibrium. Compared with wild-type Ile/Ile homozygotes, the relative risks for Phe/Phe homozygote infants was 6.87 (P value 3.0 × 10-3 ), while that for Ile/Phe heterozygotes was not significant. Assuming an autosomal recessive model, the relative risks for Phe/Phe genotype resulted 10.54 (P value 2.9 × 10-5 ), with a 3.6% population attributable risk. No parent-of-origin effect was observed. The identification in lysyl oxidase like 3 of a missense variant which under a recessive model associates with 10-fold increased risk of non-syndromic cleft palate supports the hypothesis that the genetic etiology of this congenital anomaly includes relatively uncommon recessive variants with moderate penetrance and located in genes which are also involved in syndromes that include cleft palate as part of the phenotype. Our findings require functional validation and replication in a larger independent genetic association study.

Maternal association and influence of DHFR 19 bp deletion variant predisposes foetus to anencephaly susceptibility: a family-based triad study

Objective: Previous studies have not used family-based methods to evaluate maternal-paternal genetic effects of the folate metabolizing enzyme, dihydro folate reductase (DHFR) essential during embryogenesis. Present study focuses on evaluating the association and influence of parental genetic effects of DHFR 19 bp deletion in the development of foetal neural tube defects (NTDs) using family-based triad approach.Materials and methods: The study population (n = 924) including 124 NTD case-parent trios (n = 124 × 3 = 372) and 184 healthy control-parent trios (n = 184 × 3 = 552) from Telangana, India, was genotyped for DHFR 19 bp deletion. Statistical analysis was used by SPSS and parent-of-origin effects (POE).Results: Foetuses with deletion genotype (DD) were at risk of developing anencephaly (OR = 3.26, p = 0.020). Among parents, increased maternal risk of having an anencephaly foetus (OR = 2.66, p = 0.028) was observed in mothers with DD genotype. In addition, POE analysis also demonstrated higher risk of maternal transmission of the deletion allele to anencephaly foetus compared with paternal transmission (OR = 6.00, p = 0.016). Interestingly, maternal-paternal-offspring genotype incompatibility revealed maternal deletion genotype (DD) in association with paternal heterozygous deletion genotype (WD) significantly increased risk for NTDs (OR = 5.29, p = 0.013).Conclusions: This study, using family-based case-parent and control-parent triad approach, is the first to report influence of maternal transmission of DHFR 19 bp deletion in the development of anencephaly in the foetus.

Analysis of Parent-of-Origin Effects on the X Chromosome in Asian and European Orofacial Cleft Triads Identifies Associations with DMD, FGF13, EGFL6, and Additional Loci at Xp22.2.

Background: Although both the mother's and father's alleles are present in the offspring, they may not operate at the same level. These parent-of-origin (PoO) effects have not yet been explored on the X chromosome, which motivated us to develop new methods for detecting such effects. Orofacial clefts (OFCs) exhibit sex-specific differences in prevalence and are examples of traits where a search for various types of effects on the X chromosome might be relevant.Materials and Methods: We upgraded our R-package Haplin to enable genome-wide analyses of PoO effects, as well as power simulations for different statistical models. 14,486 X-chromosome SNPs in 1,291 Asian and 1,118 European case-parent triads of isolated OFCs were available from a previous GWAS. For each ethnicity, cleft lip with or without cleft palate (CL/P) and cleft palate only (CPO) were analyzed separately using two X-inactivation models and a sliding-window approach to haplotype analysis. In addition, we performed analyses restricted to female offspring.Results: Associations were identified in “Dystrophin” (DMD, Xp21.2-p21.1), “Fibroblast growth factor 13” (FGF13, Xq26.3-q27.1) and “EGF-like domain multiple 6” (EGFL6, Xp22.2), with biologically plausible links to OFCs. Unlike EGFL6, the other associations on chromosomal region Xp22.2 had no apparent connections to OFCs. However, the Xp22.2 region itself is of potential interest because it contains genes for clefting syndromes [for example, “Oral-facial-digital syndrome 1” (OFD1) and “Midline 1” (MID1)]. Overall, the identified associations were highly specific for ethnicity, cleft subtype and X-inactivation model, except for DMD in which associations were identified in both CPO and CL/P, in the model with X-inactivation and in Europeans only.Discussion/Conclusion: The specificity of the associations for ethnicity, cleft subtype and X-inactivation model underscores the utility of conducting subanalyses, despite the ensuing need to adjust for additional multiple testing. Further investigations are needed to confirm the associations with DMD, EGF16, and FGF13. Furthermore, chromosomal region Xp22.2 appears to be a hotspot for genes implicated in clefting syndromes and thus constitutes an exciting direction to pursue in future OFCs research. More generally, the new methods presented here are readily adaptable to the study of X-linked PoO effects in other outcomes that use a family-based design.

Simulating autosomal genotypes with realistic linkage disequilibrium and a spiked-in genetic effect

BackgroundTo evaluate statistical methods for genome-wide genetic analyses, one needs to be able to simulate realistic genotypes. We here describe a method, applicable to a broad range of association study designs, that can simulate autosome-wide single-nucleotide polymorphism data with realistic linkage disequilibrium and with spiked in, user-specified, single or multi-SNP causal effects.ResultsOur construction uses existing genome-wide association data from unrelated case-parent triads, augmented by including a hypothetical complement triad for each triad (same parents but with a hypothetical offspring who carries the non-transmitted parental alleles). We assign offspring qualitative or quantitative traits probabilistically through a specified risk model and show that our approach destroys the risk signals from the original data. Our method can simulate genetically homogeneous or stratified populations and can simulate case-parents studies, case-control studies, case-only studies, or studies of quantitative traits. We show that allele frequencies and linkage disequilibrium structure in the original genome-wide association sample are preserved in the simulated data. We have implemented our method in an R package (TriadSim) which is freely available at the comprehensive R archive network.ConclusionWe have proposed a method for simulating genome-wide SNP data with realistic linkage disequilibrium. Our method will be useful for developing statistical methods for studying genetic associations, including higher order effects like epistasis and gene by environment interactions.

Parent-of-origin-environment interactions in case-parent triads with or without independent controls.

With case–parent triad data, one can frequently deduce parent of origin of the child's alleles. This allows a parent‐of‐origin (PoO) effect to be estimated as the ratio of relative risks associated with the alleles inherited from the mother and the father, respectively. A possible cause of PoO effects is DNA methylation, leading to genomic imprinting. Because environmental exposures may influence methylation patterns, gene–environment interaction studies should be extended to allow for interactions between PoO effects and environmental exposures (i.e., PoOxE). One should thus search for loci where the environmental exposure modifies the PoO effect.We have developed an extensive framework to analyze PoOxE effects in genome‐wide association studies (GWAS), based on complete or incomplete case–parent triads with or without independent control triads. The interaction approach is based on analyzing triads in each exposure stratum using maximum likelihood estimation in a log‐linear model. Interactions are then tested applying a Wald‐based posttest of parameters across strata. Our framework includes a complete setup for power calculations. We have implemented the models in the R software package Haplin.To illustrate our PoOxE test, we applied the new methodology to top hits from our previous GWAS, assessing whether smoking during the periconceptional period modifies PoO effects on cleft palate only.

A new approach to chromosome-wide analysis of X-linked markers identifies new associations in Asian and European case-parent triads of orofacial clefts.

BackgroundGWAS discoveries on the X-chromosome are underrepresented in the literature primarily because the analytical tools that have been applied were originally designed for autosomal markers. Our objective here is to employ a new robust and flexible tool for chromosome-wide analysis of X-linked markers in complex traits. Orofacial clefts are good candidates for such analysis because of the consistently observed excess of females with cleft palate only (CPO) and excess of males with cleft lip with or without cleft palate (CL/P).MethodsGenotypes for 14,486 X-chromosome SNPs in 1,291 Asian and 1,118 European isolated cleft triads were available from a previously published GWAS. The R-package HAPLIN enables genome-wide–level analyses as well as statistical power simulations for a range of biologic scenarios. We analyzed isolated CL/P and isolated CPO for each ethnicity in HAPLIN, using a sliding-window approach to haplotype analysis and two different statistical models, with and without X-inactivation in females.ResultsThere was a larger number of associations in the Asian versus the European sample, and similar to previous reports that have analyzed the same GWAS dataset using different methods, we identified associations with EFNB1/PJA1 and DMD. In addition, new associations were detected with several other genes, among which KLHL4, TBX22, CPXCR1 and BCOR were noteworthy because of their roles in clefting syndromes. A few of the associations were only detected by one particular X-inactivation model, whereas a few others were only detected in one sex.Discussion/ConclusionWe found new support for the involvement of X-linked variants in isolated clefts. The associations were specific for ethnicity, sex and model parameterization, highlighting the need for flexible tools that are capable of detecting and estimating such effects. Further efforts are needed to verify and elucidate the potential roles of EFNB1/PJA1, KLHL4, TBX22, CPXCR1 and BCOR in isolated clefts.

Transmission analysis of TGFB1 gene polymorphisms in non-syndromic cleft lip with or without cleft palate

ObjectivesTransforming growth factor beta1 (TGF-β1) plays a significant role in craniofacial development. Previous linkage studies reported that the TGF-β1-locus at 19q13.1 harbour predisposing genes for non-syndromic oral clefts. In the present study case parents triads were evaluated to find the transmission effects of genetic variants in TGF- β1 towards non-syndromic cleft lip or palate (NSCL/P). MethodsUsing allelic discrimination method148 families (case-parent triads) were assessed for single nucleotide polymorphisms (SNPs) in TGF-β1 gene. The SNPs were checked for mendelian errors and Hardy-Weinberg equilibrium (HWE). Transmission disequilibrium test and haplotype frequencies were estimated. ResultsThe TGF-β1 SNPs showed very low minor allele frequencies (MAFs) and observed heterozygosity (Hobs). The transmission disequilibrium test (TDT) and parent-of-origin likelihood ratio tests (PO-LRT) were not significant for any of the SNPs tested. Strong linkage disequilibrium (r2 = 0.722) was found between rs1800469 and rs1800470 SNPs. Haplotype analysis ignoring parent of origin showed strong evidence of excess transmission but it is not significant (p-value = 0.293). ConclusionTransmission of minor alleles were not observed from either parent indicating that the TGF-β1 gene polymorphisms by themselves do not confer risk for non-syndromic oral clefts but, rather, modify the stability and the activation process of TGF-β1. As the number of families included in the study are less, results must be considered still preliminary and require replication using more families.