RLIM Is a Candidate Dosage-Sensitive Gene for Individuals with Varying Duplications of Xq13, Intellectual Disability, and Distinct Facial Features.

Interpretation of the significance of maternally inherited X chromosome variants in males with neurocognitive phenotypes continues to present a challenge to clinical geneticists and diagnostic laboratories. Here we report 14 males from 9 families with duplications at the Xq13.2-q13.3 locus with a common facial phenotype, intellectual disability (ID), distinctive behavioral features, and a seizure disorder in two cases. All tested carrier mothers had normal intelligence. The duplication arose de novo in three mothers where grandparental testing was possible. In one family the duplication segregated with ID across three generations. RLIM is the only gene common to our duplications. However, flanking genes duplicated in some but not all the affected individuals included the brain-expressed genes NEXMIF, SLC16A2, and the long non-coding RNA gene FTX. The contribution of the RLIM-flanking genes to the phenotypes of individuals with different size duplications has not been fully resolved. Missense variants in RLIM have recently been identified to cause X-linked ID in males, with heterozygous females typically having normal intelligence and highly skewed X chromosome inactivation. We detected consistent and significant increase of RLIM mRNA and protein levels in cells derived from seven affected males from five families with the duplication. Subsequent analysis of MDM2, one of the targets of the RLIM E3 ligase activity, showed consistent downregulation in cells from the affected males. All the carrier mothers displayed normal RLIM mRNA levels and had highly skewed X chromosome inactivation. We propose that duplications at Xq13.2-13.3 including RLIM cause a recognizable but mild neurocognitive phenotype in hemizygous males.

Low risk of embryonic and other cancers in PIK3CA-related overgrowth spectrum: Impact on screening recommendations.

The PIK3CA-related overgrowth spectrum (PROS) encompasses various conditions caused by mosaic activating PIK3CA variants. PIK3CA somatic variants are also involved in various cancer types. Some generalized overgrowth syndromes are associated with an increased risk of Wilms tumor (WT). In PROS, abdominal ultrasound surveillance has been advocated to detect WT. We aimed to determine the risk of embryonic and other types of tumors in patients with PROS in order to evaluate surveillance relevance. We searched the clinical charts from 267 PROS patients for the diagnosis of cancer, and reviewed the medical literature for the risk of cancer. In our cohort, six patients developed a cancer (2.2%), and Kaplan Meier analyses estimated cumulative probabilities of cancer occurrence at 45 years of age was 5.6% (95% CI = 1.35%-21.8%). The presence of the PIK3CA variant was only confirmed in two out of four tumor samples. In the literature and our cohort, six cases of Wilms tumor/nephrogenic rests (0.12%) and four cases of other cancers have been reported out of 483 proven PIK3CA patients, in particular the p.(His1047Leu/Arg) variant. The risk of WT in PROS being lower than 5%, this is insufficient evidence to recommend routine abdominal imaging. Long-term follow-up studies are needed to evaluate the risk of other cancer types, as well as the relationship with the extent of tissue mosaicism and the presence or not of the variant in the tumor samples.

Integrative approach to interpret DYRK1A variants, leading to a frequent neurodevelopmental disorder.

PURPOSE: DYRK1A syndrome is among the most frequent monogenic forms of intellectual disability (ID). We refined the molecular and clinical description of this disorder and developed tools to improve interpretation of missense variants, which remains a major challenge in human genetics. METHODS: We reported clinical and molecular data for 50 individuals with ID harboring DYRK1A variants and developed (1) a specific DYRK1A clinical score; (2) amino acid conservation data generated from 100 DYRK1A sequences across different taxa; (3) in vitro overexpression assays to study level, cellular localization, and kinase activity of DYRK1A mutant proteins; and (4) a specific blood DNA methylation signature. RESULTS: This integrative approach was successful to reclassify several variants as pathogenic. However, we questioned the involvement of some others, such as p.Thr588Asn, still reported as likely pathogenic, and showed it does not cause an obvious phenotype in mice. CONCLUSION: Our study demonstrated the need for caution when interpreting variants in DYRK1A, even those occurring de novo. The tools developed will be useful to interpret accurately the variants identified in the future in this gene.

Whole genome paired-end sequencing elucidates functional and phenotypic consequences of balanced chromosomal rearrangement in patients with developmental disorders.

BACKGROUND: Balanced chromosomal rearrangements associated with abnormal phenotype are rare events, but may be challenging for genetic counselling, since molecular characterisation of breakpoints is not performed routinely. We used next-generation sequencing to characterise breakpoints of balanced chromosomal rearrangements at the molecular level in patients with intellectual disability and/or congenital anomalies. METHODS: Breakpoints were characterised by a paired-end low depth whole genome sequencing (WGS) strategy and validated by Sanger sequencing. Expression study of disrupted and neighbouring genes was performed by RT-qPCR from blood or lymphoblastoid cell line RNA. RESULTS: Among the 55 patients included (41 reciprocal translocations, 4 inversions, 2 insertions and 8 complex chromosomal rearrangements), we were able to detect 89% of chromosomal rearrangements (49/55). Molecular signatures at the breakpoints suggested that DNA breaks arose randomly and that there was no major influence of repeated elements. Non-homologous end-joining appeared as the main mechanism of repair (55% of rearrangements). A diagnosis could be established in 22/49 patients (44.8%), 15 by gene disruption (KANSL1, FOXP1, SPRED1, TLK2, MBD5, DMD, AUTS2, MEIS2, MEF2C, NRXN1, NFIX, SYNGAP1, GHR, ZMIZ1) and 7 by position effect (DLX5, MEF2C, BCL11B, SATB2, ZMIZ1). In addition, 16 new candidate genes were identified. Systematic gene expression studies further supported these results. We also showed the contribution of topologically associated domain maps to WGS data interpretation. CONCLUSION: Paired-end WGS is a valid strategy and may be used for structural variation characterisation in a clinical setting.

Fetal phenotype of Rubinstein-Taybi syndrome caused by CREBBP mutations.

Rubinstein-Taybi syndrome (RSTS; OMIM 180849) is an autosomal dominant developmental disorder characterized by facial dysmorphism, broad thumbs and halluces associated with intellectual disability. RSTS is caused by alterations in CREBBP (about 60%) and EP300 genes (8%). RSTS is often diagnosed at birth or during early childhood but generally not suspected during antenatal period. We report nine cases of well-documented fetal RSTS. Two cases were examined after death in utero at 18 and 35 weeks of gestation and seven cases after identification of ultrasound abnormalities and termination of pregnancy. On prenatal sonography, a large gallbladder was detected in two cases, and brain malformations were noted in four cases, especially cerebellar hypoplasia. However, the diagnosis of RSTS has not been suggested during pregnancy. Fetal autopsy showed that all fetuses had large thumbs and/or suggestive facial dysmorphism. A CREBBP gene anomaly was identified in all cases. Alterations were similar to those found in typical RSTS children. This report will contribute to a better knowledge of the fetal phenotype to consider the hypothesis of RSTS during pregnancy. Genotyping allows reassuring genetic counseling.

BCL11B mutations in patients affected by a neurodevelopmental disorder with reduced type 2 innate lymphoid cells.

The transcription factor BCL11B is essential for development of the nervous and the immune system, and Bcl11b deficiency results in structural brain defects, reduced learning capacity, and impaired immune cell development in mice. However, the precise role of BCL11B in humans is largely unexplored, except for a single patient with a BCL11B missense mutation, affected by multisystem anomalies and profound immune deficiency. Using massively parallel sequencing we identified 13 patients bearing heterozygous germline alterations in BCL11B. Notably, all of them are affected by global developmental delay with speech impairment and intellectual disability; however, none displayed overt clinical signs of immune deficiency. Six frameshift mutations, two nonsense mutations, one missense mutation, and two chromosomal rearrangements resulting in diminished BCL11B expression, arose de novo. A further frameshift mutation was transmitted from a similarly affected mother. Interestingly, the most severely affected patient harbours a missense mutation within a zinc-finger domain of BCL11B, probably affecting the DNA-binding structural interface, similar to the recently published patient. Furthermore, the most C-terminally located premature termination codon mutation fails to rescue the progenitor cell proliferation defect in hippocampal slice cultures from Bcl11b-deficient mice. Concerning the role of BCL11B in the immune system, extensive immune phenotyping of our patients revealed alterations in the T cell compartment and lack of peripheral type 2 innate lymphoid cells (ILC2s), consistent with the findings described in Bcl11b-deficient mice. Unsupervised analysis of 102 T lymphocyte subpopulations showed that the patients clearly cluster apart from healthy children, further supporting the common aetiology of the disorder. Taken together, we show here that mutations leading either to BCL11B haploinsufficiency or to a truncated BCL11B protein clinically cause a non-syndromic neurodevelopmental delay. In addition, we suggest that missense mutations affecting specific sites within zinc-finger domains might result in distinct and more severe clinical outcomes.

Whole exome sequencing identifies mutations in 10% of patients with familial non-syndromic cleft lip and/or palate in genes mutated in well-known syndromes.

BACKGROUND: Oral clefts, that is, clefts of the lip and/or cleft palate (CL/P), are the most common craniofacial birth defects with an approximate incidence of ~1/700. To date, physicians stratify patients with oral clefts into either syndromic CL/P (syCL/P) or non-syndromic CL/P (nsCL/P) depending on whether the CL/P is associated with another anomaly or not. In general, patients with syCL/P follow Mendelian inheritance, while those with nsCL/P have a complex aetiology and, as such, do not adhere to Mendelian inheritance. Genome-wide association studies have identified approximately 30 risk loci for nsCL/P, which could explain a small fraction of heritability. METHODS: To identify variants causing nsCL/P, we conducted whole exome sequencing on 84 individuals with nsCL/P, drawn from multiplex families (n=46). RESULTS: We identified rare damaging variants in four genes known to be mutated in syCL/P: TP63 (one family), TBX1 (one family), LRP6 (one family) and GRHL3 (two families), and clinical reassessment confirmed the isolated nature of their CL/P. CONCLUSION: These data demonstrate that patients with CL/P without cardinal signs of a syndrome may still carry a mutation in a gene linked to syCL/P. Rare coding and non-coding variants in syCL/P genes could in part explain the controversial question of 'missing heritability' for nsCL/P. Therefore, gene panels designed for diagnostic testing of syCL/P should be used for patients with nsCL/P, especially when there is at least third-degree family history. This would allow a more precise management, follow-up and genetic counselling. Moreover, stratified cohorts would allow hunting for genetic modifiers.

Chromosomal rearrangements in the 11p15 imprinted region: 17 new 11p15.5 duplications with associated phenotypes and putative functional consequences.

BACKGROUND: The 11p15 region contains two clusters of imprinted genes. Opposite genetic and epigenetic anomalies of this region result in two distinct growth disturbance syndromes: Beckwith-Wiedemann (BWS) and Silver-Russell syndromes (SRS). Cytogenetic rearrangements within this region represent less than 3% of SRS and BWS cases. Among these, 11p15 duplications were infrequently reported and interpretation of their pathogenic effects is complex. OBJECTIVES: To report cytogenetic and methylation analyses in a cohort of patients with SRS/BWS carrying 11p15 duplications and establish genotype/phenotype correlations. METHODS: From a cohort of patients with SRS/BWS with an abnormal methylation profile (using ASMM-RTQ-PCR), we used SNP-arrays to identify and map the 11p15 duplications. We report 19 new patients with SRS (n=9) and BWS (n=10) carrying de novo or familial 11p15 duplications, which completely or partially span either both telomeric and centromeric domains or only one domain. RESULTS: Large duplications involving one complete domain or both domains are associated with either SRS or BWS, depending on the parental origin of the duplication. Genotype-phenotype correlation studies of partial duplications within the telomeric domain demonstrate the prominent role of IGF2, rather than H19, in the control of growth. Furthermore, it highlights the role of CDKN1C within the centromeric domain and suggests that the expected overexpression of KCNQ1OT1 from the paternal allele (in partial paternal duplications, excluding CDKN1C) does not affect the expression of CDKN1C. CONCLUSIONS: The phenotype associated with 11p15 duplications depends on the size, genetic content, parental inheritance and imprinting status. Identification of these rare duplications is crucial for genetic counselling.

Diagnostic strategy in segmentation defect of the vertebrae: a retrospective study of 73 patients.

BACKGROUND: Segmentation defects of the vertebrae (SDV) are non-specific features found in various syndromes. The molecular bases of SDV are not fully elucidated due to the wide range of phenotypes and classification issues. The genes involved are in the Notch signalling pathway, which is a key system in somitogenesis. Here we report on mutations identified in a diagnosis cohort of SDV. We focused on spondylocostal dysostosis (SCD) and the phenotype of these patients in order to establish a diagnostic strategy when confronted with SDV. PATIENTS AND METHODS: We used DNA samples from a cohort of 73 patients and performed targeted sequencing of the five known SCD-causing genes (DLL3, MESP2, LFNG, HES7 and TBX6) in the first 48 patients and whole-exome sequencing (WES) in 28 relevant patients. RESULTS: Ten diagnoses, including four biallelic variants in TBX6, two biallelic variants in LFNG and DLL3, and one in MESP2 and HES7, were made with the gene panel, and two diagnoses, including biallelic variants in FLNB and one variant in MEOX1, were made by WES. The diagnostic yield of the gene panel was 10/73 (13.7%) in the global cohort but 8/10 (80%) in the subgroup meeting the SCD criteria; the diagnostic yield of WES was 2/28 (8%). CONCLUSION: After negative array CGH, targeted sequencing of the five known SCD genes should only be performed in patients who meet the diagnostic criteria of SCD. The low proportion of candidate genes identified by WES in our cohort suggests the need to consider more complex genetic architectures in cases of SDV.

Unmasking familial CPX by WES and identification of novel clinical signs.

Mutations in the T-Box transcription factor gene TBX22 are found in X-linked Cleft Palate with or without Ankyloglossia syndrome (CPX syndrome). In addition to X-linked inheritance, ankyloglossia, present in the majority of CPX patients, is an important diagnostic marker, but it is frequently missed or unreported, as it is a "minor" feature. Other described anomalies include cleft lip, micro and/or hypodontia, and features of CHARGE syndrome. We conducted whole exome sequencing (WES) on 22 individuals from 17 "a priori" non-syndromic cleft lip and/or cleft palate (CL/P) families. We filtered the data for heterozygous pathogenic variants within a set of predefined candidate genes. Two canonical splice-site mutations were found in TBX22. Detailed re-phenotyping of the two probands and their families unravelled orofacial features previously not associated with the CPX phenotypic spectrum: choanal atresia, Pierre-Robin sequence, and overgrowths on the posterior edge of the hard palate, on each side of the palatal midline. This study emphasizes the importance of WES analysis in familial CLP cases, combined with deep (reverse) phenotyping in "a priori" non-syndromic clefts.

Prenatal diagnosis of femoral facial syndrome: Three case reports and literature review.

Facial femoral syndrome (FFS) is a rare congenital abnormality, also known as femoral hypoplasia-unusual facies syndrome, characterized by variable degrees of femoral hypoplasia, associated with specific facial features. Other organ malformations are sometimes present. Most cases are sporadic, but rare family observations suggest genetic origin. However, no chromosomal or genetic abnormalities have ever been incriminated. We conducted a comprehensive literature review and added three new unreported observations. Through these 92 cases, authors aimed to determine sonographic signs that should direct towards diagnosis, and discuss potential genetic etiology. Diagnosis was suspected prenatally in 27.2% of cases, and maternal diabetes was found in 42.4% of patients. When fetal karyotype was available, it was normal in 97.1% of cases, but genomic variations of unknown significance were discovered in all three cases in which array comparative genomic hybridization (CGH) techniques were applied. Femoral affection defining FFS was hypoplasia in 78.3% of cases, agenesis in 12%, and both in 9.8%. Affection was bilateral in 84.8% of cases. Retrognathia was present in 65.2% of cases, cleft lip and/or palate in 63%, and other organ malformations in 53.3%. Intellectual development was normal in 79.2% of cases. Better prenatal recognition of this pathology, notably frequently associated malformations, should lead to a more precise estimation of functional prognosis. It seems likely that today's tendency to systematically employ array-CGH and exome/genome sequencing methods to investigate malformative sequences will allow the identification of a causal genetic abnormality in the near future.

ALDH1A3 mutations cause recessive anophthalmia and microphthalmia.

Anophthalmia and microphthalmia (A/M) are early-eye-development anomalies resulting in absent or small ocular globes, respectively. A/M anomalies occur in syndromic or nonsyndromic forms. They are genetically heterogeneous, some mutations in some genes being responsible for both anophthalmia and microphthalmia. Using a combination of homozygosity mapping, exome sequencing, and Sanger sequencing, we identified homozygosity for one splice-site and two missense mutations in the gene encoding the A3 isoform of the aldehyde dehydrogenase 1 (ALDH1A3) in three consanguineous families segregating A/M with occasional orbital cystic, neurological, and cardiac anomalies. ALDH1A3 is a key enzyme in the formation of a retinoic acid gradient along the dorso-ventral axis during early eye development. Transitory expression of mutant ALDH1A3 open reading frames showed that both missense mutations reduce the accumulation of the enzyme, potentially leading to altered retinoic acid synthesis. Although the role of retinoic acid signaling in eye development is well established, our findings provide genetic evidence of a direct link between retinoic-acid-synthesis dysfunction and early-eye-development anomalies in humans.

KBP-cytoskeleton interactions underlie developmental anomalies in Goldberg-Shprintzen syndrome.

Goldberg-Shprintzen syndrome (GOSHS, MIM #609460) is an autosomal recessive disorder of intellectual disability, specific facial gestalt and Hirschsprung's disease (HSCR). In 2005, homozygosity mapping in a large consanguineous family identified KIAA1279 as the disease-causing gene. KIAA1279 encodes KIF-binding protein (KBP), whose function is incompletely understood. Studies have identified either the mitochondria or the cytoskeleton as the site of KBP localization and interactions. To better delineate the KIAA1279-related clinical spectrum and the molecular mechanisms involved in GOSHS, we studied five new patients from three different families. The homozygous KIAA1279 mutations in these patients (p.Arg90X, p.Ser200X or p.Arg202IlefsX2) led to nonsense-mediated mRNA decay and loss of KBP function. Despite the absence of functional KBP, respiratory chain complex activity in patient fibroblasts was normal. KBP did not co-localize with mitochondria in control human fibroblasts, but interacted with the actin and tubulin cytoskeleton. KBP expression directly affected neurite growth in a neuron-like cell line (human neuroblastoma SH-SY5Y), in keeping with the central (polymicrogyria) and enteric (HSCR) neuronal developmental defects seen in GOSHS patients. The KBP interactions with actin filaments and microtubules (MTs) demonstrated in our study constitute the first evidence that an actin MT cross-link protein is involved in neuronal development in humans.

Clinical and molecular characterization of the 20q11.2 microdeletion syndrome: six new patients.

Interstitial microdeletions of 20q chromosome are rare, only 17 patients have been reported in the literature to date. Among them, only six carried a proximal 20q11.21-q11.23 deletion, with a size ranging from 2.6 to 6.8 Mb. The existence of a 20q11.2 microdeletion syndrome has been proposed, based on five previously reported cases that displayed anomalies of the extremities, intellectual disability, feeding difficulties, craniofacial dysmorphism and variable malformations. To further characterize this syndrome, we report on six new patients with 20q11.2 microdeletions diagnosed by whole-genome array-based comparative genomic hybridization. These patient reports more precisely refined the phenotype and narrowed the minimal critical region involved in this syndrome. Careful clinical assessment confirms the distinctive clinical phenotype. The craniofacial dysmorphism consists of high forehead, frontal bossing, enophthalmos, and midface hypoplasia. We have identified a 1.62 megabase minimal critical region involved in this syndrome encompassing three genes­GDF5, EPB41L1, andSAMHD1­which are strong candidates for different aspects of the phenotype. These results support that 20q11.2 microdeletion syndrome is a new contiguous gene deletion syndrome with a recognizable phenotype.

A patient with Simpson-Golabi-Behmel syndrome, biliary cirrhosis and successful liver transplantation.

Simpson-Golabi-Behmel syndrome type 1 (SGBS1) -OMIM 312870- is a rare X-linked inherited overgrowth syndrome caused by a loss of function mutation in the GPC3 gene. Affected patients present a variable phenotype with pre- and post-natal macrosomia, distinctive facial dysmorphism, organomegaly, and multiple congenital anomalies. Intellectual disability is not constant. About 10% of patients have an increased risk of developing embryonic tumors in early childhood. Only one case of biliary disease has been described so far. GPC3 is localized on Xq26. It encodes for glypican 3, a heparan sulfate proteoglycan, which among its different known roles, negatively regulates liver regeneration and hepatocyte proliferation. This report concerns a male with a SGBS1, carrier of a GPC3 pathogenic mutation, and neonatal liver disease, who developed an early biliary cirrhosis. Together with the associated risk of cancer and developmental delay, liver transplantation was discussed and then successfully performed at the age of 19 months. A hypothesis on the role of GPC3 in the patient's liver disease is also proposed.

Phenotypic spectrum of Simpson-Golabi-Behmel syndrome in a series of 42 cases with a mutation in GPC3 and review of the literature.

Simpson-Golabi-Behmel syndrome (SGBS) is a rare X-linked multiple congenital abnormality/intellectual disability syndrome characterized by pre- and post-natal overgrowth, distinctive craniofacial features, macrocephaly, variable congenital malformations, organomegaly, increased risk of tumor and mild/moderate intellectual deficiency. In 1996, Glypican 3 (GPC3) was identified as the major gene causing SGBS but the mutation detection rate was only 28-70%, suggesting either genetic heterogeneity or that some patients could have alternative diagnoses. This was particularly suggested by some reports of atypical cases with more severe prognoses. In the family reported by Golabi and Rosen, a duplication of GPC4 was recently identified, suggesting that GPC4 could be the second gene for SGBS but no point mutations within GPC4 have yet been reported. In the genetics laboratory in Tours Hospital, GPC3 molecular testing over more than a decade has detected pathogenic mutations in only 8.7% of individuals with SGBS. In addition, GPC4 mutations have not been identified thus raising the question of frequent misdiagnosis. In order to better delineate the phenotypic spectrum of SGBS caused by GPC3 mutations, and to try to define specific clinical criteria for GPC3 molecular testing, we reviewed the clinical features of all male cases with a GPC3 mutation identified in the two molecular laboratories providing this test in France (Tours and Paris). We present here the results of the analysis of 42 patients belonging to 31 families and including five fetuses and three deceased neonates.

Mutations in WNT10A are frequently involved in oligodontia associated with minor signs of ectodermal dysplasia.

Ectodermal dysplasias (ED) are a clinically and genetically heterogeneous group of hereditary disorders that have in common abnormal development of ectodermal derivatives. Hypohidrotic ectodermal dysplasia (HED) is characterized by abnormal development of eccrine sweat glands, hair, and teeth. The X-linked form of the disease, caused by mutations in the EDA gene, represents the majority of patients with the hypohidrotic form. Autosomal dominant and autosomal recessive forms are occasionally seen, and result from mutations in at least three genes (WNT10A, EDAR, or more rarely EDARADD). We have screened for mutations in EDAR (commonly involved in the hypohidrotic form) and WNT10A (involved in a wide spectrum of ED and in isolated hypodontia) in a cohort of 36 patients referred for EDA molecular screening, which failed to identify any mutation. We identified eight EDAR mutations in five patients (two with homozygous mutations, one with compound heterozygous mutations, and two with heterozygous mutation), four of which were novel variants. We identified 28 WNT10A mutations in 16 patients (5 with homozygous mutations, 7 with compound heterozygous mutations, and 4 with heterozygous mutations), seven of which were novel variants. Our study allows a more precise definition of the phenotypic spectrum associated with EDAR and WNT10A mutations and underlines the importance of the implication of WNT10A among patients with ED.

Monoallelic CRMP1 gene variants cause neurodevelopmental disorder.

Collapsin response mediator proteins (CRMPs) are key for brain development and function. Here, we link CRMP1 to a neurodevelopmental disorder. We report heterozygous de novo variants in the CRMP1 gene in three unrelated individuals with muscular hypotonia, intellectual disability, and/or autism spectrum disorder. Based on in silico analysis these variants are predicted to affect the CRMP1 structure. We further analyzed the effect of the variants on the protein structure/levels and cellular processes. We showed that the human CRMP1 variants impact the oligomerization of CRMP1 proteins. Moreover, overexpression of the CRMP1 variants affect neurite outgrowth of murine cortical neurons. While altered CRMP1 levels have been reported in psychiatric diseases, genetic variants in CRMP1 gene have never been linked to human disease. We report for the first-time variants in the CRMP1 gene and emphasize its key role in brain development and function by linking directly to a human neurodevelopmental disease.

ARX polyalanine expansions are highly implicated in familial cases of mental retardation with infantile epilepsy and/or hand dystonia.

Mutations in the ARX gene cause both nonsyndromic and several forms of syndromic mental retardation (MR). Two polyalanine (polyA) expansions of ARX are recurrent mutations. The most common one, the c.428_451dup, is associated with a wide spectrum of phenotypes, ranging from the most severe West syndrome to Partington syndrome (MR and hand dystonia), and even nonsyndromic X-linked mental retardation (NS-XLMR). Studies of patients not selected for specific clinical signs showed that the c.428_451dup is relatively frequent in families harboring X-linked MR (7.5%), but less common in familial cases compatible with X-linked NR (1%), and very rare in sporadic cases (0.1%). The c.333_334ins(GCG)7 expansion is less frequent and mainly associated with West syndrome. We screened for both ARX polyA expansions in 98 unrelated patients selected for the presence of NR associated with different types of epilepsy and/or with hand dystonia. We also studied two families with an initial diagnosis of NS-XLMR, one of which was identified as showing linkage to the ARX locus. The c.428_451dup was identified in three patients and the c.333_334ins(GCG)7 in one; all of the patients were from families with two affected brothers. We also found the c.428_451dup in the family linked to ARX, and clinical re-evaluation showed subtle, previously undetected signs. Our study illustrates that ARX polyA expansions are primarily associated with syndromic MR and shows a higher yield (18% in our cohort) when these mutations are screened in familial cases of MR with epilepsy and/or dystonia.

Maternal Transmission Ratio Distortion of GNAS Loss-of-Function Mutations.

Pseudohypoparathyroidism type 1A (PHP1A) and pseudopseudohypoparathyroidism (PPHP) are two rare autosomal dominant disorders caused by loss-of-function mutations in the imprinted Guanine Nucleotide Binding Protein, Alpha Stimulating Activity (GNAS) gene, coding Gs α. PHP1A is caused by mutations in the maternal allele and results in Albright's hereditary osteodystrophy (AHO) and hormonal resistance, mainly to the parathormone (PTH), whereas PPHP, with AHO features and no hormonal resistance, is linked to mutations in the paternal allele. This study sought to investigate parental transmission of GNAS mutations. We conducted a retrospective study in a population of 204 families with 361 patients harboring GNAS mutations. To prevent ascertainment bias toward a higher proportion of affected children due to the way in which data were collected, we excluded from transmission analysis all probands in the ascertained sibships. After bias correction, the distribution ratio of the mutated alleles was calculated from the observed genotypes of the offspring of nuclear families and was compared to the expected ratio of 50% according to Mendelian inheritance (one-sample Z-test). Sex ratio, phenotype of the transmitting parent, and transmission depending on the severity of the mutation were also analyzed. Transmission analysis was performed in 114 nuclear families and included 250 descendants. The fertility rates were similar between male and female patients. We showed an excess of transmission from mother to offspring of mutated alleles (59%, p = .022), which was greater when the mutations were severe (61.7%, p = .023). Similarly, an excess of transmission was found when the mother had a PHP1A phenotype (64.7%, p = .036). By contrast, a Mendelian distribution was observed when the mutations were paternally inherited. Higher numbers of females within the carriers, but not in noncarriers, were also observed. The mother-specific transmission ratio distortion (TRD) and the sex-ratio imbalance associated to PHP1A point to a role of Gs α in oocyte biology or embryogenesis, with implications for genetic counseling. © 2019 American Society for Bone and Mineral Research.