Heterogeneity LOD Research Articles

Detecting genetic loci for preservation of cognition in the Midwestern United States Amish

AbstractBackgroundAlzheimer’s Disease (AD) is the most common form of dementia and has limited treatments. While AD risk has a large genetic component, under 50% of the genetic risk has been identified. By focusing on identifying genetic variants that delay or prevent the onset of AD, our goal is to identify new associated genes and variants. To detect such loci, we studied cognitive preservation in the Midwestern Amish, a genetically and culturally isolated population of European descent.MethodsWe studied 946 Amish individuals (ages 76‐95) from Ohio and Indiana. Participants were classified as cognitively impaired (33.8%) or cognitively unimpaired (66.2%) by consensus review of cognitive examinations. These individuals were all connected in a 15‐generation 8,222‐person pedigree. This pedigree was divided into 104 sub‐pedigrees via PedCut for linkage analysis. MERLIN was used for autosomal linkage analysis, while MINX was used for X‐chromosome linkage analysis. The association analysis, corrected for genetic relationship, used GENESIS for autosomes and XWAS for the X chromosome.ResultsOver 250,000 SNPs were used for association and two‐point linkage analyses, and a subset of 5,294 uncorrelated SNPs was used for multipoint linkage analyses. on 15 different chromosomes, with the highest two‐point heterogeneity LOD score (HLOD = 5.85) on chromosome 2 (∼79Mb) and highest multipoint HLOD (3.55) on chromosome 12 (∼25Mb), neither overlapping with known AD genes. Two linkage results overlapped with known AD genes (Chr 6: CD2AP; Chr 11: PICALM) and do not overlap with association results. Significant (p ≤ 6.4x10‐7) and suggestive (p ≤ 1x10‐4) thresholds for association were determined using SimpleM. While no significant associations were found, suggestive associations were found for 103 SNPs (11 loci) across 10 chromosomes. Three of these (chr 11: MS4A2; chr 14: SLC24A4; chr 16: IQCK) fall near known AD genes. These significant and suggestive regions are being followed up currently with fine mapping.ConclusionPreliminary analyses suggest that using cognitive preservation as our phenotype of interest identifies both known AD loci and novel regions that warrant further evaluation and may lead to a further understanding of both AD and cognitive preservation.

Genome-wide scans of myopia in Pennsylvania Amish families reveal significant linkage to 12q15, 8q21.3 and 5p15.33.

Myopia is one of the most common ocular disorders in the world, yet the genetic etiology of the disease remains poorly understood. Specialized founder populations, such as the Pennsylvania Amish, provide the opportunity to utilize exclusive genomic architecture, like unique haplotypes, to better understand the genetic causes of myopia. We perform genetic linkage analysis on Pennsylvania Amish families that have a strong familial history of myopia to map any potential causal variants and genes for the disease. 293 individuals from 25 extended families were genotyped on the Illumina ExomePlus array and merged with previous microsatellite data. We coded myopia affection as a binary phenotype; myopia was defined as having a mean spherical equivalent (MSE) of less than or equal to - 1 D (diopters). Two-point and multipoint parametric linkage analyses were performed under an autosomal dominant model. When allowing for locus heterogeneity, we identified two novel genome-wide significantly linked variants at 12q15 (heterogeneity LOD, HLOD = 3.77) in PTPRB and at 8q21.3 (HLOD = 3.35) in CNGB3. We identified further three genome-wide significant variants within a single family. These three variants were located in exons of SLC6A18 at 5p15.33 (LODs ranged from 3.51 to 3.37). Multipoint analysis confirmed the significant signal at 5p15.33 with six genome-wide significant variants (LODs ranged from 3.6 to 3.3). Further suggestive evidence of linkage was observed in several other regions of the genome. All three novel linked regions contain strong candidate genes, especially CNGB3 on 8q21.3, which has been shown to affect photoreceptors and cause complete color blindness. Whole genome sequencing on these regions is planned to conclusively elucidate the causal variants.

Linkage Analysis of the Chromosome 5q31-33 Region Identifies JAKMIP2 as a Risk Factor for Graves' Disease in the Chinese Han Population.

BackgroundThis study aimed to investigate susceptibility to Graves’s disease and the association with the 5q32–33.1 region on chromosome 5 in a Chinese Han population.Material/MethodsEighty Chinese Han multiplex families included first-degree and second-degree relatives with Graves’ disease. Eight microsatellite markers on chromosome 5 at the 5q32–33.1 region underwent linkage analysis and the association between the regions D5S1480–D5S2014 were studied.ResultsThe maximal heterogeneity logarithm of the odds (HLOD) score of D5S2090 was 4.29 (α=0.42) and of D5S2014 was 4.01 (α=0.34). A nonparametric linkage (NPL) score of 3.14 (P<0.001) was found for D5S2014. The D5S1480–D5S2014 region on chromosome 5 was associated with Graves’ disease, with eight haplotype domains. There were significant differences in the sixth and eighth haplotype domains between patients with Graves’ disease compared with normal individuals. Tagging single nucleotide polymorphisms (SNPs) of the sixth and eighth haplotype domains showed that individuals with SNP62 (rs12653715 G/C) who were GG homozygous had a significantly increased risk of Graves’ disease compared GC heterozygous or CC homozygous individuals. The transmission disequilibrium test (TDT) indicated that SNP62 (rs12653715) and SNP63 (rs12653081) loci in the Janus kinase and microtubule interacting protein 2 (JAKMIP2) gene showed dominant transmission from heterozygous parents to the affected offspring, and SNPs in the secretoglobin family 3A member 2 (SCGB3A2) gene showed no transmission disequilibrium. The haplotype JAKMIP2-1 was identified as being particularly significant.ConclusionsJAKMIP2 gene polymorphism require further study as potential risk factors for Graves’ disease in the Chinese Han population.

Rare genetic variation implicated in non-Hispanic white families with Alzheimer disease.

ObjectiveTo identify genetic variation influencing late-onset Alzheimer disease (LOAD), we used a large data set of non-Hispanic white (NHW) extended families multiply-affected by LOAD by performing whole genome sequencing (WGS).MethodsAs part of the Alzheimer Disease Sequencing Project, WGS data were generated for 197 NHW participants from 42 families (affected individuals and unaffected, elderly relatives). A two-pronged approach was taken. First, variants were prioritized using heterogeneity logarithm of the odds (HLOD) and family-specific LOD scores as well as annotations based on function, frequency, and segregation with disease. Second, known Alzheimer disease (AD) candidate genes were assessed for rare variation using a family-based association test.ResultsWe identified 41 rare, predicted-damaging variants that segregated with disease in the families that contributed to the HLOD or family-specific LOD regions. These included a variant in nitric oxide synthase 1 adaptor protein that segregates with disease in a family with 7 individuals with AD, as well as variants in RP11-433J8, ABCA1, and FISP2. Rare-variant association identified 2 LOAD candidate genes associated with disease in these families: FERMT2 (p-values = 0.001) and SLC24A4 (p-value = 0.009). These genes still showed association while controlling for common index variants, indicating the rare-variant signal is distinct from common variation that initially identified the genes as candidates.ConclusionsWe identified multiple genes with putative damaging rare variants that segregate with disease in multiplex AD families and showed that rare variation may influence AD risk at AD candidate genes. These results identify novel AD candidate genes and show a role for rare variation in LOAD etiology, even at genes previously identified by common variation.

Whole-Genome Linkage Scan Combined With Exome Sequencing Identifies Novel Candidate Genes for Carotid Intima-Media Thickness.

Carotid intima-media thickness (cIMT) is an established heritable marker for subclinical atherosclerosis. In this study, we aim to identify rare variants with large effects driving differences in cIMT by performing genome-wide linkage analysis of individuals in the extremes of cIMT trait distribution (>90th percentile) in a large family-based study from a genetically isolated population in the Netherlands. Linked regions were subsequently explored by fine-mapping using exome sequencing. We observed significant evidence of linkage on chromosomes 2p16.3 [rs1017418, heterogeneity LOD (HLOD) = 3.35], 19q13.43 (rs3499, HLOD = 9.09), 20p13 (rs1434789, HLOD = 4.10), and 21q22.12 (rs2834949, HLOD = 3.59). Fine-mapping using exome sequencing data identified a non-coding variant (rs62165235) in PNPT1 gene under the linkage peak at chromosome 2 that is likely to have a regulatory function. The variant was associated with quantitative cIMT in the family-based study population (effect = 0.27, p-value = 0.013). Furthermore, we identified several genes under the linkage peak at chromosome 21 highly expressed in tissues relevant for atherosclerosis. To conclude, our linkage analysis identified four genomic regions significantly linked to cIMT. Further analyses are needed to demonstrate involvement of identified candidate genes in development of atherosclerosis.

Linkage analysis of multiplex Caribbean Hispanic families loaded for unexplained early-onset cases identifies novel Alzheimer's disease loci

IntroductionLess than 10% of early-onset Alzheimer's disease (EOAD) is explained by known mutations. MethodsWe conducted genetic linkage analysis of 68 well-phenotyped Caribbean Hispanic families without clear inheritance patterns or mutations in APP, PSEN1, and PSEN2 and with two or more individuals with EOAD. ResultsWe identified 16 (logarithm of odds > 3.6) linked regions, including eight novel loci for EOAD (2p15, 5q14.1, 11p15.1, 13q21.22, 13q33.1, 16p12.1, 20p12.1, and 20q11.21) and eight regions previously associated with late-onset Alzheimer's disease. The strongest signal was observed at 16p12.1 (25 cM, 33 Mb; heterogeneity logarithm of odds = 5.3), ∼3 Mb upstream of the ceroid lipofuscinosis 3 (CLN3) gene associated with juvenile neuronal ceroid lipofuscinosis (JNCL), which functions in retromer trafficking and has been reported to alter intracellular processing of the amyloid precursor protein. DiscussionThis study supports the notion that the genetic architectures of unexplained EOAD and late-onset AD overlap partially, but not fully.

Linkage evidence and methylation at 2q region in nonsyndromic cleft lip and/or palate of Malay population

Introduction: Nonsyndromic cleft lip and/or palate (NSCLP) occurs as a result of multifactorial determinants, involving both genetic and environmental factors. Several candidate genes associated with NSCLP have been discovered through genetic approach, but there is paucity of studies focusing on epigenetic determinants in NSCLP. We are interested to reveal linkage evidence of SATB2 at 2q region in large-extended NSCLP families of Malay population and its methylation activity in causing cleft formation. Materials and Methods: Eight large-extended families were included in this study. Microarray analysis was carried out and genome-wide linkage was determined using GeneHunter Multipoint Linkage Analysis v2.1r5. SATB2 methylation was tested on 100 NSCLP patients by DNA sequencing. Results: Genome-wide linkage analysis has revealed significant nonparametric linkage score and suggestive logarithm of the odds (LOD) score at 2q region in family 50 and family 100. Genome-wide heterogeneity LOD score of 2.63 and α =0.122 were found in total families at 2q33.1-q35 region. Significant copy number loss (P < 0.05) in NSCLP family compared with the normal control supports the linkage evidence of SATB2 in those families with positive linkage. Epigenetic testing found SATB2 unmethylation at DNA promoter region. Discussion: Linkage evidence and significant low copy number of SATB2 in NSCLP family of Malay population confirmed that genetic factors play a major role in causing cleft defects. SATB2 unmethylation could not support the epigenetic occurrence in causing craniofacial deformities. Conclusions: Linkage evidence and significant low copy number of SATB2 in NSCLP family of Malay population confirmed that genetic factors play a major role in causing cleft defects. SATB2 unmethylation could not support the epigenetic occurrence in causing craniofacial deformities.

Discovery of candidate genes for nonsyndromic cleft lip palate through genome-wide linkage analysis of large extended families in the Malay population.

BackgroundNonsyndromic orofacial clefts are one of the most common birth defects worldwide. It occurs as a result of genetic or environmental factors. This study investigates the genetic contribution to nonsyndromic cleft lip and/or palate through the analysis of family pedigrees. Candidate genes associated with the condition were identified from large extended families from the Malay population.ResultsA significant nonparametric linkage (NPL) score was detected in family 100. Other suggestive NPL and logarithm of the odds (LOD) scores were attained from families 50, 58, 99 and 100 under autosomal recessive mode. Heterogeneity LOD (HLOD) score ≥ 1 was determined for all families, confirming genetic heterogeneity of the population and indicating that a proportion of families might be linked to each other. Several candidate genes in linkage intervals were determined; LPHN2 at 1p31, SATB2 at 2q33.1-q35, PVRL3 at 3q13.3, COL21A1 at 6p12.1, FOXP2 at 7q22.3-q33, FOXG1 and HECTD1 at 14q12 and TOX3 at 16q12.1.ConclusionsWe have identified several novel and known candidate genes for nonsyndromic cleft lip and/or palate through genome-wide linkage analysis. Further analysis of the involvement of these genes in the condition will shed light on the disease mechanism. Comprehensive genetic testing of the candidate genes is warranted.

Whole-genome single nucleotide polymorphism-based linkage analysis in spondyloarthritis multiplex families reveals a new susceptibility locus in 13q13

ObjectiveSpondyloarthritis (SpA) is a chronic inflammatory disorder with high heritability but with complex genetics. Apart from HLA-B27, most of the underlying genetic components remain to be identified. We conducted a...

Linkage analysis in a Dutch population isolate shows no major gene for left-handedness or atypical language lateralization.

Cerebral dominance of language function and hand preference are suggested to be heritable traits with possible shared genetic background. However, joined genetic studies of these traits have never been conducted. We performed a genetic linkage study in 37 multigenerational human pedigrees of both sexes (consisting of 355 subjects) enriched with left-handedness in which we also measured language lateralization. Hand preference was measured with the Edinburgh Handedness Inventory, and language lateralization was measured with functional transcranial Doppler during language production. The estimated heritability of left-handedness and language lateralization in these pedigrees is 0.24 and 0.31, respectively. A parametric major gene model was tested for left-handedness. Nonparametric analyses were performed for left-handedness, atypical lateralization, and degree of language lateralization. We did not observe genome-wide evidence for linkage in the parametric or nonparametric analyses for any of the phenotypes tested. However, multiple regions showed suggestive evidence of linkage. The parametric model showed suggestive linkage for left-handedness in the 22q13 region [heterogeneity logarithm of odds (HLOD) = 2.18]. Nonparametric multipoint analysis of left-handedness showed suggestive linkage in the same region [logarithm of odds (LOD) = 2.80]. Atypical language lateralization showed suggestive linkage in the 7q34 region (LODMax = 2.35). For strength of language lateralization, we observed suggestive linkage in the 6p22 (LODMax = 2.54), 7q32 (LODMax = 1.93), and 9q33 (LODMax = 2.10) regions. We did not observe any overlap of suggestive genetic signal between handedness and the extent of language lateralization. The absence of significant linkage argues against the presence of a major gene coding for both traits; rather, our results are suggestive of these traits being two independent polygenic complex traits.

Positional cloning and next-generation sequencing identified a TGM6 mutation in a large Chinese pedigree with acute myeloid leukaemia.

An inherited predisposition to acute myeloid leukaemia (AML) is exceedingly rare, but the investigation of these families will aid in the delineation of the underlying mechanisms of the more common, sporadic cases. Three AML predisposition genes, RUNX1, CEBPA and GATA2, have been recognised, but the culprit genes in the majority of AML pedigrees remain obscure. We applied a combined strategy of linkage analysis and next-generation sequencing (NGS) technology in an autosomal-dominant AML Chinese family with 11 cases in four generations. A genome-wide linkage scan using a 500K SNP genotyping array was conducted to identify a previously unreported candidate region on 20p13 with a maximum multipoint heterogeneity LOD (HLOD) score of 3.56 (P=0.00005). Targeted NGS within this region and whole-exome sequencing (WES) revealed a missense mutation in TGM6 (RefSeq, NM_198994.2:c.1550T>G, p.(L517W)), which cosegregated with the phenotype in this family, and was absent in 530 healthy controls. The mutated amino acid was located in a highly conserved position, which may be deleterious and affect the activation of TGM6. Our results strongly support the candidacy of TGM6 as a novel familial AML-associated gene.

Investigation of a putative melanoma susceptibility locus at chromosome 3q29

Malignant melanoma, the most fatal form of skin cancer, is currently increasing in incidence in many populations. Approximately 10% of all cases occur in families with an inherited predisposition for melanoma. In Sweden, only a minor portion of such melanoma families carry a mutation in the known melanoma gene CDKN2A, and there is a need to identify additional melanoma susceptibility genes. In a recently performed genome-wide linkage screen, novel loci with suggestive evidence of linkage to melanoma were detected. In this study, we have further analyzed one region on chromosome 3q29. In all, 89 affected and 15 nonaffected family members from 42 melanoma-prone families were genotyped for 34 genetic markers. In a pooled linkage analysis of all 42 families, we detected significant evidence of linkage, with a maximum heterogeneity logarithm of odds (HLOD) score of 3.1 with 83% of the families contributing to the linkage score. The minimum critical region of linkage (defined by a 1LOD score support interval) maps to chromosome 3q29, spans 3.5 Mb of genomic sequence, and harbors 44 identified genes. Sequence variants within this region have previously been associated with cancer susceptibility. This study reports the presence of a putative novel melanoma susceptibility locus in the Swedish population, a finding that needs to be replicated in an independent study on other individuals with familial melanoma. Sequencing of genes in the region may identify novel melanoma-associated mutations.

Evidence for linkage of migraine in Rolandic epilepsy to known 1q23 FHM2 and novel 17q22 genetic loci

Migraine headaches are a common comorbidity in Rolandic epilepsy (RE) and familial aggregation of migraine in RE families suggests a genetic basis not mediated by seizures. We performed a genome-wide linkage analysis of the migraine phenotype in 38 families with RE to localize potential genetic contribution, with a follow-up in an additional 21 families at linked loci. We used two-point and multipoint LOD (logarithm of the odds) score methods for linkage, maximized over genetic models. We found evidence of linkage to migraine at chromosome 17q12-22 [multipoint HLOD (heterogeneity LOD) 4.40, recessive, 99% penetrance], replicated in the second dataset (HLOD 2.61), and suggestive evidence at 1q23.1-23.2, centering over the FHM2 locus (two-point LOD 3.00 and MP HLOD 2.52). Sanger sequencing in 14 migraine-affected individuals found no coding mutations in the FHM2 gene ATP1A2. There was no evidence of pleiotropy for migraine and either reading or speech disorder, or the electroencephalographic endophenotype of RE when the affected definition was redefined as those with migraine or the comorbid phenotype, and pedigrees were reanalyzed for linkage. In summary, we report a novel migraine susceptibility locus at 17q12-22, and a second locus that may contribute to migraine in the general population at 1q23.1-23.2. Comorbid migraine in RE appears genetically influenced, but we did not obtain evidence that the identified susceptibility loci are consistent with pleiotropic effects on other comorbidities in RE. Loci identified here should be fine-mapped in individuals from RE families with migraine, and prioritized for analysis in other types of epilepsy-associated migraine.

Linkage and association of successful aging to the 6q25 region in large Amish kindreds

Successful aging (SA) is a multidimensional phenotype involving living to older age with high physical function, preserved cognition, and continued social engagement. Several domains underlying SA are heritable, and identifying health-promoting polymorphisms and their interactions with the environment could provide important information regarding the health of older adults. In the present study, we examined 263 cognitively intact Amish individuals age 80 and older (74 SA and 189 "normally aged") all of whom are part of a single 13-generation pedigree. A genome-wide association study of 630,309 autosomal single nucleotide polymorphisms (SNPs) was performed and analyzed for linkage using multipoint analyses and for association using the modified quasi-likelihood score test. There was evidence for linkage on 6q25-27 near the fragile site FRA6E region with a dominant model maximum multipoint heterogeneity LOD score = 3.2. The 1-LOD-down support interval for this linkage contained one SNP for which there was regionally significant evidence of association (rs205990, p = 2.36 × 10(-5)). This marker survived interval-wide Bonferroni correction for multiple testing and was located between the genes QKI and PDE10A. Other areas of chromosome 6q25-q27 (including the FRA6E region) contained several SNPs associated with SA (minimum p = 2.89 × 10(-6)). These findings suggest potentially novel genes in the 6q25-q27 region linked and associated with SA in the Amish; however, these findings should be verified in an independent replication cohort.

Analysis of Xq27-28 linkage in the international consortium for prostate cancer genetics (ICPCG) families

BackgroundGenetic variants are likely to contribute to a portion of prostate cancer risk. Full elucidation of the genetic etiology of prostate cancer is difficult because of incomplete penetrance and genetic and phenotypic heterogeneity. Current evidence suggests that genetic linkage to prostate cancer has been found on several chromosomes including the X; however, identification of causative genes has been elusive.MethodsParametric and non-parametric linkage analyses were performed using 26 microsatellite markers in each of 11 groups of multiple-case prostate cancer families from the International Consortium for Prostate Cancer Genetics (ICPCG). Meta-analyses of the resultant family-specific linkage statistics across the entire 1,323 families and in several predefined subsets were then performed.ResultsMeta-analyses of linkage statistics resulted in a maximum parametric heterogeneity lod score (HLOD) of 1.28, and an allele-sharing lod score (LOD) of 2.0 in favor of linkage to Xq27-q28 at 138 cM. In subset analyses, families with average age at onset less than 65 years exhibited a maximum HLOD of 1.8 (at 138 cM) versus a maximum regional HLOD of only 0.32 in families with average age at onset of 65 years or older. Surprisingly, the subset of families with only 2–3 affected men and some evidence of male-to-male transmission of prostate cancer gave the strongest evidence of linkage to the region (HLOD = 3.24, 134 cM). For this subset, the HLOD was slightly increased (HLOD = 3.47 at 134 cM) when families used in the original published report of linkage to Xq27-28 were excluded.ConclusionsAlthough there was not strong support for linkage to the Xq27-28 region in the complete set of families, the subset of families with earlier age at onset exhibited more evidence of linkage than families with later onset of disease. A subset of families with 2–3 affected individuals and with some evidence of male to male disease transmission showed stronger linkage signals. Our results suggest that the genetic basis for prostate cancer in our families is much more complex than a single susceptibility locus on the X chromosome, and that future explorations of the Xq27-28 region should focus on the subset of families identified here with the strongest evidence of linkage to this region.

Genome-Wide Linkage Analysis of Obsessive-Compulsive Disorder Implicates Chromosome 1p36

Obsessive-compulsive disorder (OCD) has a complex etiology involving both genetic and environmental factors. However, the genetic causes of OCD are largely unknown, despite the identification of several promising candidate genes and linkage regions. Our objective was to conduct genetic linkage studies of the type of OCD thought to have the strongest genetic etiology (i.e., childhood-onset OCD), in 33 Caucasian families with ≥2 childhood-onset OCD-affected individuals from the United States (n = 245 individuals with genotype data). Parametric and nonparametric genome-wide linkage analyses were conducted with Morgan and Merlin in these families using a selected panel of single nucleotide repeat polymorphisms from the Illumina 610-Quad Bead Chip. The initial analyses were followed by fine-mapping analyses in genomic regions with initial heterogeneity logarithm of odds (HLOD) scores of ≥2.0. We identified five areas of interest (HLOD score ≥2) on chromosomes 1p36, 2p14, 5q13, 6p25, and 10p13. The strongest result was on chromosome 1p36.33-p36.32 (HLOD = 3.77, suggestive evidence for linkage after fine mapping). At this location, several of the families showed haplotypes co-segregating with OCD. The results of this study represent the strongest linkage finding for OCD in a primary analysis to date and suggest that chromosome 1p36, and possibly several other genomic regions, may harbor susceptibility loci for OCD. Multiple brain-expressed genes lie under the primary linkage peak (approximately 4 megabases in size). Follow-up studies, including replication in additional samples and targeted sequencing of the areas of interest, are needed to confirm these findings and to identify specific OCD risk variants.

Genome‐wide linkage meta‐analysis identifies susceptibility loci at 2q34 and 13q31.3 for genetic generalized epilepsies

Genetic generalized epilepsies (GGEs) have a lifetime prevalence of 0.3% with heritability estimates of 80%. A considerable proportion of families with siblings affected by GGEs presumably display an oligogenic inheritance. The present genome-wide linkage meta-analysis aimed to map: (1) susceptibility loci shared by a broad spectrum of GGEs, and (2) seizure type-related genetic factors preferentially predisposing to either typical absence or myoclonic seizures, respectively. Meta-analysis of three genome-wide linkage datasets was carried out in 379 GGE-multiplex families of European ancestry including 982 relatives with GGEs. To dissect out seizure type-related susceptibility genes, two family subgroups were stratified comprising 235 families with predominantly genetic absence epilepsies (GAEs) and 118 families with an aggregation of juvenile myoclonic epilepsy (JME). To map shared and seizure type-related susceptibility loci, both nonparametric loci (NPL) and parametric linkage analyses were performed for a broad trait model (GGEs) in the entire set of GGE-multiplex families and a narrow trait model (typical absence or myoclonic seizures) in the subgroups of JME and GAE families. For the entire set of 379 GGE-multiplex families, linkage analysis revealed six loci achieving suggestive evidence for linkage at 1p36.22, 3p14.2, 5q34, 13q12.12, 13q31.3, and 19q13.42. The linkage finding at 5q34 was consistently supported by both NPL and parametric linkage results across all three family groups. A genome-wide significant nonparametric logarithm of odds score of 3.43 was obtained at 2q34 in 118 JME families. Significant parametric linkage to 13q31.3 was found in 235 GAE families assuming recessive inheritance (heterogeneity logarithm of odds = 5.02). Our linkage results support an oligogenic predisposition of familial GGE syndromes. The genetic risk factor at 5q34 confers risk to a broad spectrum of familial GGE syndromes, whereas susceptibility loci at 2q34 and 13q31.3 preferentially predispose to myoclonic seizures or absence seizures, respectively. Phenotype- genotype strategies applying narrow trait definitions in phenotypic homogeneous subgroups of families improve the prospects of disentangling the genetic basis of common familial GGE syndromes.

Chromosome 2p14 is linked to susceptibility to leprosy.

BackgroundA genetic component to the etiology of leprosy is well recognized but the mechanism of inheritance and the genes involved are yet to be fully established.MethodologyA genome-wide single nucleotide polymorphism (SNP) based linkage analysis was carried out using 23 pedigrees, each with 3 to 7 family members affected by leprosy. Multipoint parametric and non-parametric linkage analyses were performed using MERLIN 1.1.1.Principal FindingsGenome-wide significant evidence for linkage was identified on chromosome 2p14 with a heterogeneity logarithm of odds (HLOD) score of 3.51 (rs1106577) under a recessive model of inheritance, while suggestive evidence was identified on chr.4q22 (HLOD 2.92, rs1349350, dominant model), chr. 8q24 (HLOD 2.74, rs1618523, recessive model) and chr.16q24 (HLOD 1.93, rs276990 dominant model). Our study also provided moderate evidence for a linkage locus on chromosome 6q24–26 by non-parametric linkage analysis (rs6570858, LOD 1.54, p = 0.004), overlapping a previously reported linkage region on chromosome 6q25–26.ConclusionA genome-wide linkage analysis has identified a new linkage locus on chromosome 2p14 for leprosy in Pedigrees from China.

Extended Kindred With Recessive Late-Onset Alzheimer Disease Maps to Locus 8p22-p21.2

Late-onset Alzheimer disease (LOAD) is a complex genetic disorder. Although genes involved in early-onset forms were discovered more than a decade ago, LOAD research has only been able to point out small effect loci, with the exception of APOE. We mapped the gene predisposing to LOAD in an extended inbred family coming from a genetically isolated region (24 sampled individuals, 12 of whom are affected), completing a genome-wide screen with an Affymetrix10 K single nucleotide polymorphism microarray. Genotyping results were evaluated under model-dependent (dominant and recessive) and model-free analysis. We obtained a maximum nonparametric linkage score of 3.24 (P=0.00006) on chromosome 8p22-p21.2. The same genomic position also yielded the highest multipoint heterogeneity LOD (HLOD) under a recessive model (HLOD=3.04). When we compared the results of the model-dependent analysis, a higher score was obtained in the recessive model (3.04) than in the dominant model (1.0). This is a new locus identified in LOAD, in chromosome 8p22-p21.2 and encompassing several candidate genes, among them CLU and PPP3CC that were excluded by sequencing. The finding of a recessive model of inheritance, consistent with the assumption of inbreeding as a morbidity factor in this population, supports the notion of a role of recessive genes in LOAD.

Linkage Analysis of X Chromosome in Spontaneous Preterm Birth

Background: Preterm birth accounts for 2-3 million annual deaths worldwide and is the major cause of acute and chronic morbidity in children. More than 50% of preterm births have a spontaneous onset. Family studies suggest that genetic factors affect the risk of spontaneous preterm birth (SPTB). However, the genetic background is poorly known.Aim: To search for X chromosomal regions associating with SPTB using linkage analysis.Methods: Seven large northern Finnish families with recurrent SPTBs and maternal transmission were selected for the study. DNA samples from family members were genotyped using Affymetrix 500Kb Array, consisting of 500,568 single-nucleotide polymorphism markers. Results of linkage analysis using autosomal markers in this array were previously reported; here the results of X chromosomal markers are presented. Analyze, v. 1.9.3 BETA, was used in parametric two-point linkage analysis of SPTB.Results: Linkage analysis revealed three markers with significant signals (heterogeneity LOD score, HLOD >3) when the infant was studied as affected: rs6525299 (HLOD=3.72), rs11266593 (HLOD=3.05), and rs7056400 (HLOD=3.05). The first marker is located on chromosome locus Xq13.1 and the latter two on Xq21.1. Three interesting genes located near these loci were identified: those encoding androgen receptor (AR), interleukin 2 receptor, gamma (IL2RG), and chemokine (C-X-C motif) receptor 3 (CXCR3). These genes will be considered as candidates for SPTB in an upcoming case-control study of SPTB.Conclusions: This is the first linkage study of X chromosomal markers in SPTB. We identified three potential candidate genes that may play a role in the pathology of SPTB.