Maternal Allele Research Articles

New insights into the imprinted MEG8-DMR in 14q32 and clinical and molecular description of novel patients with Temple syndrome

The chromosomal region 14q32 contains several imprinted genes, which are expressed either from the paternal (DLK1 and RTL1) or the maternal (MEG3, RTL1as and MEG8) allele only. Imprinted expression of these genes is regulated by two differentially methylated regions (DMRs), the germline DLK1/MEG3 intergenic (IG)-DMR (MEG3/DLK1:IG-DMR) and the somatic MEG3-DMR (MEG3:TSS-DMR), which are methylated on the paternal and unmethylated on the maternal allele. Disruption of imprinting in the 14q32 region results in two clinically distinct imprinting disorders, Temple syndrome (TS14) and Kagami-Ogata syndrome (KOS14). Another DMR with a yet unknown function is located in intron 2 of MEG8 (MEG8-DMR, MEG8:Int2-DMR). In contrast to the IG-DMR and the MEG3-DMR, this somatic DMR is methylated on the maternal chromosome and unmethylated on the paternal chromosome. We have performed extensive methylation analyses by deep bisulfite sequencing of the IG-DMR, MEG3-DMR and MEG8-DMR in different prenatal tissues including amniotic fluid cells and chorionic villi. In addition, we have studied the methylation pattern of the MEG8-DMR in different postnatal tissues. We show that the MEG8-DMR is hypermethylated in each of 13 non-deletion TS14 patients (seven newly identified and six previously published patients), irrespective of the underlying molecular cause, and is always hypomethylated in the four patients with KOS14, who have different deletions not encompassing the MEG8-DMR itself. The size and the extent of the deletions and the resulting methylation pattern suggest that transcription starting from the MEG3 promoter may be necessary to establish the methylation imprint at the MEG8-DMR.

Analysis of case-parent trios for imprinting effect using a loglinear model with adjustment for sex-of-parent-specific transmission ratio distortion.

Transmission ratio distortion (TRD) is a phenomenon where parental transmission of disease allele to the child does not follow the Mendelian inheritance ratio. TRD occurs in a sex-of-parent-specific or non-sex-of-parent-specific manner. An offset computed from the transmission probability of the minor allele in control-trios can be added to the loglinear model to adjust for TRD. Adjusting the model removes the inflation in the genotype relative risk (RR) estimate and Type 1 error introduced by non-sex-of-parent-specific TRD. We now propose to further extend this model to estimate an imprinting parameter. Some evidence suggests that more than 1% of all mammalian genes are imprinted. In the presence of imprinting, for example, the offspring inheriting an over-transmitted disease allele from the parent with a higher expression level in a neighboring gene is over-represented in the sample. TRD mechanisms such as meiotic drive and gametic competition occur in a sex-of-parent-specific manner. Therefore, sex-of-parent-specific TRD (ST) leads to over-representation of maternal or paternal alleles in the affected child. As a result, ST may bias the imprinting effect when present in the sample. We propose a sex-of-parent-specific transmission offset in adjusting the loglinear model to account for ST. This extended model restores the correct RR estimates for child and imprinting effects, adjusts for inflation in Type 1 error, and improves performance on sensitivity and specificity compared to the original model without ST offset. We conclude that to correctly interpret the association signal of an imprinting effect, adjustment for ST is necessary to ensure valid conclusions.

Single-cell multi-omics sequencing of mouse early embryos and embryonic stem cells

Single-cell epigenome sequencing techniques have recently been developed. However, the combination of different layers of epigenome sequencing in an individual cell has not yet been achieved. Here, we developed a single-cell multi-omics sequencing technology (single-cell COOL-seq) that can analyze the chromatin state/nucleosome positioning, DNA methylation, copy number variation and ploidy simultaneously from the same individual mammalian cell. We used this method to analyze the reprogramming of the chromatin state and DNA methylation in mouse preimplantation embryos. We found that within < 12 h of fertilization, each individual cell undergoes global genome demethylation together with the rapid and global reprogramming of both maternal and paternal genomes to a highly opened chromatin state. This was followed by decreased openness after the late zygote stage. Furthermore, from the late zygote to the 4-cell stage, the residual DNA methylation is preferentially preserved on intergenic regions of the paternal alleles and intragenic regions of maternal alleles in each individual blastomere. However, chromatin accessibility is similar between paternal and maternal alleles in each individual cell from the late zygote to the blastocyst stage. The binding motifs of several pluripotency regulators are enriched at distal nucleosome depleted regions from as early as the 2-cell stage. This indicates that the cis-regulatory elements of such target genes have been primed to an open state from the 2-cell stage onward, long before pluripotency is eventually established in the ICM of the blastocyst. Genes may be classified into homogeneously open, homogeneously closed and divergent states based on the chromatin accessibility of their promoter regions among individual cells. This can be traced to step-wise transitions during preimplantation development. Our study offers the first single-cell and parental allele-specific analysis of the genome-scale chromatin state and DNA methylation dynamics at single-base resolution in early mouse embryos and provides new insights into the heterogeneous yet highly ordered features of epigenomic reprogramming during this process.

Maternal GRB10 microdeletion is a novel cause of cystic placenta: Spectrum of genomic changes in the etiology of enlarged cystic placenta

IntroductionThe genetics and pathology of diploid complete and triploid partial hydatidiform moles have been well established. Enlarged cystic placenta often indicates an underlying etiology and is frequently associated with adverse pregnancy outcome. Several imprinted genes are strongly expressed in placental tissues and essential for normal placental growth and development. Disruption of these imprinted genes can lead to abnormal placental pathology and placental stunting or overgrowth. We present the genetic etiologies of five unusual mosaic cases of enlarged cystic placentas and report a novel etiology, mosaicism for deletion of the maternal GRB10 gene. MethodsFive mosaic placental mesenchymal dysplasia cases with discrete populations of “cystic” and “normal” villi and/or atypical p57KIP2 immunostaining were evaluated by genetic analysis; including G-banded karyotyping, fluorescence in situ hybridization (FISH), whole genome CGH + SNP microarray, conventional Sanger sequencing, and STR microsatellite analysis. ResultsGenetic etiologies ranged from genome-wide changes, including mosaic androgenetic isodisomy and mosaic diandric triploidy, to a novel microdeletion of the maternally-expressed GRB10 gene. An abnormal mosaic population of cells was also detected in the fetus in two cases. DiscussionFour cases were mosaic for either diandric triploidy or an androgenetic cell population, and the enlarged cystic placentas were likely due to an excess of paternally-expressed growth promoting genes and also the absence of maternally-expressed growth restricting genes. Also we identified mosaicism for a novel microdeletion of the maternal GRB10 allele, a potent growth inhibitor, which resulted in placental overgrowth in the cystic area of one placenta. We advocate the use of ancillary techniques to investigate complex mosaic cases of enlarged cystic placentas to discover atypical genetic etiologies and to increase our understanding of the placental genome.

Expression and imprinting of DIO3 and DIO3OS genes in Holstein cattle

DIO3 and DIO3OS are two imprinted genes identified in mouse and humans. The DIO3 gene, which encodes for the type 3 deiodinase, is preferentially expressed from the paternal allele, while the DIO3OS transcript is transcribed in opposite orientation to DIO3, multiple noncoding and alternatively splicing isoforms from maternal allele. In this study, the five splice variants of DIO3OS were identified in Holstein cattle and had complex, tissue-specific expression patterns observed in eight tissues, including heart, liver, spleen, lung, kidney, muscle, fat and brain. In the G+C rich region, upstream from the cattle DIO3 gene, there were three small conserved regions and some promoter elements similar to those observed in mouse and humans. An allele-specific expression analysis-based SNP method revealed that DIO3 and DIO3OS genes exhibited monoallelic expression in the eight tissues, indicating that DIO3 and DIO3OS are imprinted in cattle.

Gene silencing and a novel monoallelic expression pattern in distinct CD177 neutrophil subsets

CD177 presents antigens in allo- and autoimmune diseases on the neutrophil surface. Individuals can be either CD177-deficient or harbor distinct CD177neg and CD177pos neutrophil subsets. We studied mechanisms controlling subset-restricted CD177 expression in bimodal individuals. CD177pos, but not CD177neg neutrophils, produced CD177 protein and mRNA. Haplotype analysis indicated a unique monoallelic CD177 expression pattern, where the offspring stably transcribed either the maternal or paternal allele. Hematopoietic stem cells expressed both CD177 alleles and silenced one copy during neutrophil differentiation. ChIP and reporter assays in HeLa cells with monoallelic CD177 expression showed that methylation reduced reporter activity, whereas demethylation caused biallelic CD177 expression. HeLa cell transfection with c-Jun and c-Fos increased CD177 mRNA. Importantly, CD177pos human neutrophils, but not CD177neg neutrophils, showed a euchromatic CD177 promoter, unmethylated CpGs, and c-Jun and c-Fos binding. We describe epigenetic mechanisms explaining the two distinct CD177 neutrophil subsets and a novel monoallelic CD177 expression pattern that does not follow classical random monoallelic expression or imprinting.

A novel deletion of SNURF/SNRPN exon 1 in a patient with Prader-Willi-like phenotype

Here we report the smallest deletion involving SNURF/SNRPN that causes major symptoms of Prader-Willi syndrome (PWS), including hypotonia, dysmorphic features, intellectual disability, and obesity. A female patient with the aforementioned and additional features was referred to the Mayo Clinic Cytogenetics laboratory for genetic testing. Chromosomal microarray analysis and subsequent Sanger sequencing identified a de novo 6.4 kb deletion at 15q11.2, containing exon 1 of the SNURF gene and exon 1 of the shortest isoform of the SNRPN gene. SNURF/SNRPN exon 1, which is methylated on the silent maternal allele, is associated with acetylated histones on the expressed paternal allele. This region also overlaps with the PWS-imprinting center (IC). Subsequent molecular methylation analysis was performed using methylation-specific MLPA (MS-MLPA), which characterized that the deletion of SNURF/SNRPN exon 1 was paternal in origin, consistent with the PWS-like phenotype. Since SNURF/SNRPN gene and the PWS-IC are known to regulate snoRNAs, it is likely that the PWS-like phenotype observed in patients with paternal SNURF/SNRPN deletion is due to the disrupted expression of SNORD116 snoRNAs.

Uneven distribution of complementary sex determiner (csd) alleles in Apis mellifera population

The complementary sex determiner (csd) gene determines the sex of the western honey bee (Apis mellifera L.). Bees that are heterozygous at the csd locus develop into females; whereas hemizygous bees develop into males. The co-occurrence of two identical csd alleles in a single diploid genome leads to the genetic death of the bee. Thus, the maintenance of csd diversity in the population is favoured. The number and distribution of csd alleles is particularly interesting in light of the recent decline in the honey bee population. In this study, we analysed the distribution of csd alleles in two Polish populations separated by about 100 km. We analysed the maternal alleles of 193 colonies and found 121 different alleles. We also analysed the distribution and frequency of the alleles, and found that they are distributed unevenly. We show that the methods that have been used so far to estimate the total worldwide number of csd alleles have significantly underestimated their diversity. We also show that the uneven distribution of csd alleles is caused by a large number of infrequent alleles, which most likely results from the fact that these alleles are generated very frequently.

Hypersociability in the Angelman syndrome mouse model

Deletions and reciprocal triplications of the human chromosomal 15q11-13 region cause two distinct neurodevelopmental disorders. Maternally-derived deletions or inactivating mutations of UBE3A, a 15q11-13 gene expressed exclusively from the maternal allele in neurons, cause Angelman syndrome, characterized by intellectual disability, motor deficits, seizures, and a characteristic increased social smiling, laughing, and eye contact. Conversely, maternally-derived triplications of 15q11-13 cause a behavioral disorder on the autism spectrum with clinical features that include decreased sociability that we recently reconstituted in mice with Ube3a alone. Based on the unique sociability features reported in Angelman syndrome and the repressed sociability observed when Ube3a gene dosage is increased, we hypothesized that mice with neuronal UBE3A loss that models Angelman syndrome would display evidence of hypersocial behavior. We report that mice with maternally-inherited Ube3a gene deletion (Ube3amKO) have a prolonged preference for, and interaction with, social stimuli in the three chamber social approach task. By contrast, interactions with a novel object are reduced. Further, ultrasonic vocalizations and physical contacts are increased in male and female Ube3amKO mice paired with an unfamiliar genotype-matched female. Single housing wild type mice increased these same social behavior parameters to levels observed in Ube3amKO mice where this effect was partially occluded. These results indicate sociability is repressed by social experience and the endogenous levels of UBE3A protein and suggest some social behavioral features observed in Angelman syndrome may reflect an increased social motivation.

A Pair of Maternal Chromosomes Derived from Meiotic Nondisjunction in Trisomy 21 Affects Nuclear Architecture and Transcriptional Regulation

Eukaryotic genomes are organised into complex higher-order structures within the nucleus, and the three-dimensional arrangement of chromosomes is functionally important for global gene regulation. The existence of supernumerary chromosome 21 in Down syndrome may perturb the nuclear architecture at different levels, which is normally optimised to maintain the physiological balance of gene expression. However, it has not been clearly elucidated whether and how aberrant configuration of chromosomes affects gene activities. To investigate the effects of trisomy 21 on nuclear organisation and gene expression, we performed three-dimensional fluorescent imaging analysis of chromosome-edited human induced pluripotent stem cells (iPSCs), which enabled identification of the parental origin of the three copies of chromosome 21. We found that two copies of maternal chromosomes resulting from meiotic nondisjunction had a higher tendency to form an adjacent pair and were located relatively distant from the nuclear membrane, suggesting the conserved interaction between these homologous chromosomes. Transcriptional profiling of parental-origin-specific corrected disomy 21 iPSC lines indicated upregulated expression of the maternal alleles for a group of genes, which was accompanied by a fluctuating expression pattern. These results suggest the unique effects of a pair of maternal chromosomes in trisomy 21, which may contribute to the pathological phenotype.

Biallelic loss-of-function variants in DOCK3 cause muscle hypotonia, ataxia, and intellectual disability.

DOCK3 encodes the dedicator of cytokinesis 3 protein, a member of the DOCK180 family of proteins that are characterized by guanine-nucleotide exchange factor activity. DOCK3 is expressed exclusively in the central nervous system and plays an important role in axonal outgrowth and cytoskeleton reorganization. Dock3 knockout mice exhibit motor deficiencies with abnormal ataxic gait and impaired learning. We report 2 siblings with biallelic loss-of-function variants in DOCK3. Diagnostic whole-exome sequencing (WES) and chromosomal microarray were performed on a proband with severe developmental disability, hypotonia, and ataxic gait. Testing was also performed on the proband's similarly affected brother. A paternally inherited 458 kb deletion in chromosomal region 3p21.2 disrupting the DOCK3 gene was identified in both affected siblings. WES identified a nonsense variant c.382C>G (p.Gln128*) in the DOCK3 gene (NM_004947) on the maternal allele in both siblings. Common features in both affected individuals include severe developmental disability, ataxic gait, and severe hypotonia, which recapitulates the Dock3 knockout mouse phenotype. We show that complete DOCK3 deficiency in humans leads to developmental disability with significant hypotonia and gait ataxia, probably due to abnormal axonal development.

Maternal mutations of FOXF1 cause alveolar capillary dysplasia despite not being imprinted.

Alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV) is a rare cause of pulmonary hypertension in newborns. Maternally inherited point mutations in Forkhead Box F1 gene (FOXF1), deletions of the gene, or its long-range enhancers on the maternal allele are responsible for this neonatal lethal disorder. Here, we describe monozygotic twins and one full-term newborn with ACD and gastrointestinal malformations caused by de novo mutations of FOXF1 on the maternal-inherited alleles. Since this parental transmission is consistent with genomic imprinting, the parent-of-origin specific monoallelic expression of genes, we have undertaken a detailed analysis of both allelic expression and DNA methylation. FOXF1 and its neighboring gene FENDRR were both biallelically expressed in a wide range of fetal tissues, including lung and intestine. Furthermore, detailed methylation screening within the 16q24.1 regions failed to identify regions of allelic methylation, suggesting that disrupted imprinting is not responsible for ACDMPV.

A 15-year-long Southern blotting analysis of FMR1 to detect female carriers and for prenatal diagnosis of fragile X syndrome in Taiwan.

Here, we review the results of Southern blotting analyses of the FMR1 gene performed in our reference laboratory in Taiwan over a 15-year period. In total, 725 high-risk women with a family history of fragile X syndrome (FXS) or idiopathic intellectual disability, 3911 low-risk pregnant women without such family history, and prenatal diagnosis data for 32 foetuses from 24 carrier mothers were included. Only 2 carriers were in the low-risk group, which indicated a prevalence of 1 of 1955 women (95% confidence interval: 1/7156-1/539). A total of 100 carriers were found to be in the high-risk group, thus revealing a significantly higher frequency than the low-risk group (100/725 vs 2/3911, P<0.0001). Eight of the 14 foetuses that inherited the maternal mutant allele were verified to have a full mutation, with the smallest maternal pre-mutation allele carrying 56 CGG repeats. The overall findings confirmed that the carrier prevalence among low-risk women in Taiwan is significantly lower than that reported in western countries. Therefore, the most important step for preventing FXS in Taiwan would be to focus on high-risk women by promoting general awareness of this disease and spreading knowledge regarding the benefits of carrier screening and prenatal testing.

Awake1, an ABC-Type Transporter, Reveals an Essential Role for Suberin in the Control of Seed Dormancy.

The mother plant plays an important dynamic role in the control of dormancy of her progeny seed in response to environmental signals. In order to further understand the mechanisms by which this dormancy control takes place in Arabidopsis (Arabidopsis thaliana), we conducted a forward genetic screen to isolate mutants that fail to enter dormancy in response to variation in temperature during seed set. We show that, for the first of these mutants, designated awake1, the maternal allele is required for entry into strongly dormant states and that awake1 mutants show seed phenotypes shown previously to be associated with the loss of suberin in the seed. We identify awake1 as an allele of ABCG20, an ATP-binding cassette transporter-encoding gene required for the transport of fatty acids during suberin deposition, and show that further suberin-deficient mutants have seed dormancy defects. Seed coat suberin composition is affected by temperature during seed maturation, but this response appears to be independent of ABCG20. We conclude that seed coat suberin is essential for seed dormancy imposition by low temperature and that the exclusion of oxygen and water from the seed by the suberin and tannin layers is important for dormancy imposition.

Using Mendelian randomization to determine causal effects of maternal pregnancy (intrauterine) exposures on offspring outcomes: Sources of bias and methods for assessing them

Mendelian randomization (MR), the use of genetic variants as instrumental variables (IVs) to test causal effects, is increasingly used in aetiological epidemiology. Few of the methodological developments in MR have considered the specific situation of using genetic IVs to test the causal effect of exposures in pregnant women on postnatal offspring outcomes. In this paper, we describe specific ways in which the IV assumptions might be violated when MR is used to test such intrauterine effects. We highlight the importance of considering the extent to which there is overlap between genetic variants in offspring that influence their outcome with genetic variants used as IVs in their mothers. Where there is overlap, and particularly if it generates a strong association of maternal genetic IVs with offspring outcome via the offspring genotype, the exclusion restriction assumption of IV analyses will be violated. We recommend a set of analyses that ought to be considered when MR is used to address research questions concerned with intrauterine effects on post-natal offspring outcomes, and provide details of how these can be undertaken and interpreted. These additional analyses include the use of genetic data from offspring and fathers, examining associations using maternal non-transmitted alleles, and using simulated data in sensitivity analyses (for which we provide code). We explore the extent to which new methods that have been developed for exploring violation of the exclusion restriction assumption in the two-sample setting (MR-Egger and median based methods) might be used when exploring intrauterine effects in one-sample MR. We provide a list of recommendations that researchers should use when applying MR to test the effects of intrauterine exposures on postnatal offspring outcomes and use an illustrative example with real data to demonstrate how our recommendations can be applied and subsequent results appropriately interpreted.

Both maternally and paternally imprinted genes regulate seed development in rice

Genetic imprinting refers to the unequal expression of paternal and maternal alleles of a gene in sexually reproducing organisms, including mammals and flowering plants. Although many imprinted genes have been identified in plants, the functions of these imprinted genes have remained largely uninvestigated. We report genome-wide analysis of gene expression, DNA methylation and small RNAs in the rice endosperm and functional tests of five imprinted genes during seed development using Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated gene9 (CRISPR/Cas9) gene editing technology. In the rice endosperm, we identified 162 maternally expressed genes (MEGs) and 95 paternally expressed genes (PEGs), which were associated with miniature inverted-repeat transposable elements, imprinted differentially methylated loci and some 21-22 small interfering RNAs (siRNAs) and long noncoding RNAs (lncRNAs). Remarkably, one-third of MEGs and nearly one-half of PEGs were associated with grain yield quantitative trait loci. Most MEGs and some PEGs were expressed specifically in the endosperm. Disruption of two MEGs increased the amount of small starch granules and reduced grain and embryo size, whereas mutation of three PEGs reduced starch content and seed fertility. Our data indicate that both MEGs and PEGs in rice regulate nutrient metabolism and endosperm development, which optimize seed development and offspring fitness to facilitate parental-offspring coadaptation. These imprinted genes and mechanisms could be used to improve the grain yield of rice and other cereal crops.

Hybrid weakness in a rice interspecific hybrid is nitrogen-dependent, and accompanied by changes in gene expression at both total transcript level and parental allele partitioning.

BackgroundHybrid weakness, a phenomenon opposite to heterosis, refers to inferior growth and development in a hybrid relative to its pure-line parents. Little attention has been paid to the phenomenological or mechanistic aspect of hybrid weakness, probably due to its rare occurrence.Methodology/Principal findingsHere, using a set of interspecific triploid F1 hybrids between Oryza sativa, ssp. japonica (genome AA) and a tetraploid wild rice species, O. alta (genome, CCDD), we investigated the phenotypic and physiological differences between the F1 hybrids and their parents under normal and nitrogen-limiting conditions. We quantified the expression levels of 21 key genes involved in three important pathways pertinent to the assayed phenotypic and physiological traits by real-time qRT-PCR. Further, we assayed expression partitioning of parental alleles for eight genes in the F1 hybrids relative to the in silico “hybrids” (parental cDNA mixture) under both normal and N-limiting conditions by using locus-specific cDNA pyrosequencing.Conclusions/SignificanceWe report that the F1 hybrids showed weakness in several phenotypic traits at the final seedling-stage compared with their corresponding mid-parent values (MPVs). Nine of the 21 studied genes showed contrasted expression levels between hybrids and parents (MPVs) under normal vs. N-limiting conditions. Interestingly, under N-limiting conditions, the overtly enhanced partitioning of maternal allele expression in the hybrids for eight assayed genes echo their attenuated hybrid weakness in phenotypes, an observation further bolstered by more resemblance of hybrids to the maternal parent under N-limiting conditions compared to normal conditions in a suite of measured physiological traits. Our observations suggest that both overall expression level and differential partitioning of parental alleles of critical genes contribute to condition-specific hybrid weakness.

Epigenetic status of imprinted genes in placenta during recurrent pregnancy loss

An analysis of differential methylation of 47 imprinted genes in placenta tissues of spontaneous abortions at the first trimester of pregnancy from women with recurrent pregnancy loss or with one sporadic abortion was performed using the DNA-microarray approach. We showed that epimutations of the imprinted genes were registered significantly more often in abortions from women with recurrent miscarriage in contrast to the embryos from women with sporadic pregnancy loss with frequency of 6.2 and 3.7% per locus, respectively (p < 0.01). The predominant type of epimutation appeared to be a postzygotic hypomethylation of the imprinted genes on chromosomes of maternal origin, which was observed in the examined samples in 5.1 and 2.89% of cases, respectively. Replicative study of the methylation status of seven imprinted genes (DLK1, PEG10, PLAGL1, KCNQ1OT1, PEG3, GRB10, and PEG1/MEST) in the enlarged embryo samples supported the results of microarray analysis in respect to both epimutation frequency and predominance of somatic hypomethylation of maternal alleles. It was also demonstrated that pregnancy loss was associated with multilocus methylation defects of imprinted genes, the frequency of which was also significantly increased in the placental tissues of spontaneous abortions in women with recurrent miscarriage.

Chromosome choice for initiation of V-(D)-J recombination is not governed by genomic imprinting.

V-(D)-J recombination generates the antigen receptor diversity necessary for immune cell function while allelic exclusion ensures that each cell expresses a single antigen-receptor. V-(D)-J recombination of the Ig, Tcrb, Tcrg, and Tcrd antigen receptor genes is ordered and sequential so that only one allele generates a productive rearrangement. The mechanism controlling sequential rearrangement of antigen receptor genes, in particular, how only one allele is selected to initiate recombination while at least temporarily leaving the other intact remains unresolved. Genomic imprinting, a widespread phenomenon wherein maternal or paternal allele inheritance determines allele activity, could represent a regulatory mechanism for controlling sequential V-(D)-J rearrangement. We used strain-specific single nucleotide polymorphisms (SNPs) within antigen receptor genes to determine if maternal vs. paternal inheritance could underlie chromosomal choice for the initiation of recombination. We found no parental chromosomal bias in the initiation of V-(D)-J recombination in T or B cells, eliminating genomic imprinting as a potential regulator for this tightly regulated process.

Progressive Development of PTH Resistance in Patients With Inactivating Mutations on the Maternal Allele of GNAS.

Parathormone (PTH) resistance is characterized by hypocalcaemia, hyperphosphatemia, and elevated PTH in the absence of vitamin D deficiency. Pseudohypoparathyroidism type 1A [PHP1A, or inactivating parathormone (PTH)/PTHrp signaling disorder 2, according to the new classification (iPPSD2)], is caused by mutations in the maternal GNAS allele. To assess PTH resistance over time in 20 patients affected by iPPSD2 (PHP1A), diagnosed because of family history, ectopic ossification, or short stature, and carrying a GNAS mutation. We gathered retrospective data for calcium, phosphate, thyrotropin (TSH), and PTH levels at regular intervals. PTH infusion testing (teriparatide) was performed in 1 patient. Patients were diagnosed at a mean age of 3.9 years and had a mean follow-up of 2 years. TSH resistance was already present at diagnosis in all patients (TSH, 13.3 ± 9.0 mIU/L). Over time, PTH levels increased (179 to 306 pg/mL; P < 0.05), and calcium levels decreased (2.31 to 2.21 mmol/L; P < 0.05), but phosphate levels did not decrease with age as expected for healthy individuals. One patient born with ectopic ossifications showed an increase in cyclic adenosine monophosphate upon PTH infusion, similar to that of controls, at 7 months of age, but an impaired response at 4 years of age. In patients with iPPSD2 (PHP1A), PTH resistance and hypocalcemia develop over time. These findings highlight the importance of screening for maternal GNAS mutations in the presence of ectopic ossifications or family history, even in the absence of PTH resistance and hypocalcemia. The follow-up of these patients should include regular assessments of calcium, phosphate, and PTH levels.