Assortative mating and parental genetic relatedness contribute to the pathogenicity of variably expressive variants

We examined more than 97,000 families from four neurodevelopmental disease cohorts and the UK Biobank to identify phenotypic and genetic patterns in parents contributing to neurodevelopmental disease risk in children. We identified within- and cross-disorder correlations between six phenotypes in parents and children, such as obsessive-compulsive disorder (R = 0.32-0.38, p < 10-126). We also found that measures of sub-clinical autism features in parents are associated with several autism severity measures in children, including biparental mean Social Responsiveness Scale scores and proband Repetitive Behaviors Scale scores (regression coefficient = 0.14, p = 3.38 × 10-4). We further describe patterns of phenotypic similarity between spouses, where spouses show correlations for six neurological and psychiatric phenotypes, including a within-disorder correlation for depression (R = 0.24-0.68, p < 0.001) and a cross-disorder correlation between anxiety and bipolar disorder (R = 0.09-0.22, p < 10-92). Using a simulated population, we also found that assortative mating can lead to increases in disease liability over generations and the appearance of "genetic anticipation" in families carrying rare variants. We identified several families in a neurodevelopmental disease cohort where the proband inherited multiple rare variants in disease-associated genes from each of their affected parents. We further identified parental relatedness as a risk factor for neurodevelopmental disorders through its inverse relationship with variant pathogenicity and propose that parental relatedness modulates disease risk by increasing genome-wide homozygosity in children (R = 0.05-0.26, p < 0.05). Our results highlight the utility of assessing parent phenotypes and genotypes toward predicting features in children who carry rare variably expressive variants and implicate assortative mating as a risk factor for increased disease severity in these families.

Assortative mating and parental genetic relatedness drive the pathogenicity of variably expressive variants

We examined more than 38,000 spouse pairs from four neurodevelopmental disease cohorts and the UK Biobank to identify phenotypic and genetic patterns in parents associated with neurodevelopmental disease risk in children. We identified correlations between six phenotypes in parents and children, including correlations of clinical diagnoses such as obsessive-compulsive disorder (R=0.31-0.49, p<0.001), and two measures of sub-clinical autism features in parents affecting several autism severity measures in children, such as bi-parental mean Social Responsiveness Scale (SRS) scores affecting proband SRS scores (regression coefficient=0.11, p=0.003). We further describe patterns of phenotypic and genetic similarity between spouses, where spouses show both within- and cross-disorder correlations for seven neurological and psychiatric phenotypes, including a within-disorder correlation for depression (R=0.25-0.72, p<0.001) and a cross-disorder correlation between schizophrenia and personality disorder (R=0.20-0.57, p<0.001). Further, these spouses with similar phenotypes were significantly correlated for rare variant burden (R=0.07-0.57, p<0.0001). We propose that assortative mating on these features may drive the increases in genetic risk over generations and the appearance of "genetic anticipation" associated with many variably expressive variants. We further identified parental relatedness as a risk factor for neurodevelopmental disorders through its inverse correlations with burden and pathogenicity of rare variants and propose that parental relatedness drives disease risk by increasing genome-wide homozygosity in children (R=0.09-0.30, p<0.001). Our results highlight the utility of assessing parent phenotypes and genotypes in predicting features in children carrying variably expressive variants and counseling families carrying these variants.

1p36 deletion syndrome: Review and mapping with further characterization of the phenotype, a new cohort of 86 patients

Chromosome 1p36 deletion syndrome (1p36DS) is one of the most common terminal deletion syndromes (incidence between 1/5000 and 1/10,000 live births in the American population), due to a heterozygous deletion of part of the short arm of chromosome 1. The 1p36DS is characterized by typical craniofacial features, developmental delay/intellectual disability, hypotonia, epilepsy, cardiomyopathy/congenital heart defect, brain abnormalities, hearing loss, eyes/vision problem, and short stature. The aim of our study was to (1) evaluate the incidence of the 1p36DS in the French population compared to 22q11.2 deletion syndrome and trisomy 21; (2) review the postnatal phenotype related to microarray data, compared to previously publish prenatal data. Thanks to a collaboration with the ACLF (Association des Cytogénéticiens de Langue Française), we have collected data of 86 patients constituting, to the best of our knowledge, the second-largest cohort of 1p36DS patients in the literature. We estimated an average of at least 10 cases per year in France. 1p36DS seems to be much less frequent than 22q11.2 deletion syndrome and trisomy 21. Patients presented mainly dysmorphism, microcephaly, developmental delay/intellectual disability, hypotonia, epilepsy, brain malformations, behavioral disorders, cardiomyopathy, or cardiovascular malformations and, pre and/or postnatal growth retardation. Cardiac abnormalities, brain malformations, and epilepsy were more frequent in distal deletions, whereas microcephaly was more common in proximal deletions. Mapping and genotype-phenotype correlation allowed us to identify four critical regions responsible for intellectual disability. This study highlights some phenotypic variability, according to the deletion position, and helps to refine the phenotype of 1p36DS, allowing improved management and follow-up of patients.

Phenotypic spectrum and genomics of undiagnosed arthrogryposis multiplex congenita

BACKGROUND

Arthrogryposis multiplex congenita (AMC) is characterised by congenital joint contractures in two or more body areas. AMC exhibits wide phenotypic and genetic heterogeneity. Our goals were to improve the genetic diagnosis rates of AMC, to evaluate the added value of whole exome sequencing (WES) compared with targeted exome sequencing (TES) and to identify new genes in 315 unrelated undiagnosed AMC families.

METHODS

Several genomic approaches were used including genetic mapping of disease loci in multiplex or consanguineous families, TES then WES. Sanger sequencing was performed to identify or validate variants.

RESULTS

We achieved disease gene identification in 52.7% of AMC index patients including nine recently identified genes (CNTNAP1, MAGEL2, ADGRG6, ADCY6, GLDN, LGI4, LMOD3, UNC50 and SCN1A). Moreover, we identified pathogenic variants in ASXL3 and STAC3 expanding the phenotypes associated with these genes. The most frequent cause of AMC was a primary involvement of skeletal muscle (40%) followed by brain (22%). The most frequent mode of inheritance is autosomal recessive (66.3% of patients). In sporadic patients born to non-consanguineous parents (n=60), de novo dominant autosomal or X linked variants were observed in 30 of them (50%).

CONCLUSION

New genes recently identified in AMC represent 21% of causing genes in our cohort. A high proportion of de novo variants were observed indicating that this mechanism plays a prominent part in this developmental disease. Our data showed the added value of WES when compared with TES due to the larger clinical spectrum of some disease genes than initially described and the identification of novel genes.

Clinical characteristics of familial hypocalciuric hypercalcaemia type 1: A multicentre study of 77 adult patients

OBJECTIVE

Familial hypocalciuric hypercalcaemia type 1 (FHH1), related to heterozygous loss-of-function mutations of the calcium-sensing receptor gene, is the main differential diagnosis for primary hyperparathyroidism. The aim of our study was to describe clinical characteristics of adult patients living in France with a genetically confirmed FHH1.

DESIGN AND PATIENTS

This observational, retrospective, multicentre study included 77 adults, followed up in 32 clinical departments in France, with a genetic FHH1 diagnosis between 2001 and 2012.

RESULTS

Hypercalcaemia was diagnosed at a median age of 53 years [IQR: 38-61]. The diagnosis was made after clinical manifestations, routine analysis or familial screening in 56, 34 and 10% of cases, respectively, (n = 58; data not available for 19 patients). Chondrocalcinosis was present in 11/51 patients (22%), bone fractures in 8/56 (14%) and renal colic in 6/55 (11%). The median serum calcium was 2.74 mmol/L [IQR: 2.63-2.86 mmol/L], the median plasma parathyroid hormone level was 4.9 pmol/L [3.1-7.1], and the median 24-hour urinary calcium excretion was 2.8 mmol/24 hours [IQR: 1.9-4.0]. Osteoporosis (dual X-ray absorptiometry) or kidney stones (renal ultrasonography) were found in 6/38 patients (16%) and 9/32 patients (28%), respectively. Fourteen patients (18%) underwent parathyroid surgery; parathyroid adenoma was found in three patients (21%) and parathyroid hyperplasia in nine patients (64%). No correlation between genotype and phenotype was established.

CONCLUSION

This large cohort study demonstrates that FHH1 clinical characteristics can be atypical in 33 patients (43%). Clinicians should be aware of this rare differential diagnosis in order to adopt an appropriate treatment strategy.

De Novo SOX6 Variants Cause a Neurodevelopmental Syndrome Associated with ADHD, Craniosynostosis, and Osteochondromas

SOX6 belongs to a family of 20 SRY-related HMG-box-containing (SOX) genes that encode transcription factors controlling cell fate and differentiation in many developmental and adult processes. For SOX6, these processes include, but are not limited to, neurogenesis and skeletogenesis. Variants in half of the SOX genes have been shown to cause severe developmental and adult syndromes, referred to as SOXopathies. We here provide evidence that SOX6 variants also cause a SOXopathy. Using clinical and genetic data, we identify 19 individuals harboring various types of SOX6 alterations and exhibiting developmental delay and/or intellectual disability; the individuals are from 17 unrelated families. Additional, inconstant features include attention-deficit/hyperactivity disorder (ADHD), autism, mild facial dysmorphism, craniosynostosis, and multiple osteochondromas. All variants are heterozygous. Fourteen are de novo, one is inherited from a mosaic father, and four offspring from two families have a paternally inherited variant. Intragenic microdeletions, balanced structural rearrangements, frameshifts, and nonsense variants are predicted to inactivate the SOX6 variant allele. Four missense variants occur in residues and protein regions highly conserved evolutionarily. These variants are not detected in the gnomAD control cohort, and the amino acid substitutions are predicted to be damaging. Two of these variants are located in the HMG domain and abolish SOX6 transcriptional activity in vitro. No clear genotype-phenotype correlations are found. Taken together, these findings concur that SOX6 haploinsufficiency leads to a neurodevelopmental SOXopathy that often includes ADHD and abnormal skeletal and other features.

Pathogenic DDX3X Mutations Impair RNA Metabolism and Neurogenesis during Fetal Cortical Development

De novo germline mutations in the RNA helicase DDX3X account for 1%-3% of unexplained intellectual disability (ID) cases in females and are associated with autism, brain malformations, and epilepsy. Yet, the developmental and molecular mechanisms by which DDX3X mutations impair brain function are unknown. Here, we use human and mouse genetics and cell biological and biochemical approaches to elucidate mechanisms by which pathogenic DDX3X variants disrupt brain development. We report the largest clinical cohort to date with DDX3X mutations (n = 107), demonstrating a striking correlation between recurrent dominant missense mutations, polymicrogyria, and the most severe clinical outcomes. We show that Ddx3x controls cortical development by regulating neuron generation. Severe DDX3X missense mutations profoundly disrupt RNA helicase activity, induce ectopic RNA-protein granules in neural progenitors and neurons, and impair translation. Together, these results uncover key mechanisms underlying DDX3X syndrome and highlight aberrant RNA metabolism in the pathogenesis of neurodevelopmental disease.

Excess of de novo variants in genes involved in chromatin remodelling in patients with marfanoid habitus and intellectual disability

PURPOSE

Marfanoid habitus (MH) combined with intellectual disability (ID) (MHID) is a clinically and genetically heterogeneous presentation. The combination of array CGH and targeted sequencing of genes responsible for Marfan or Lujan-Fryns syndrome explain no more than 20% of subjects.

METHODS

To further decipher the genetic basis of MHID, we performed exome sequencing on a combination of trio-based (33 subjects) or single probands (31 subjects), of which 61 were sporadic.

RESULTS

We identified eight genes with de novo variants (DNVs) in at least two unrelated individuals (ARID1B, ATP1A1, DLG4, EHMT1, NFIX, NSD1, NUP205 and ZEB2). Using simulation models, we showed that five genes (DLG4, NFIX, EHMT1, ZEB2 and ATP1A1) met conservative Bonferroni genomewide significance for an excess of the observed de novo point variants. Overall, at least one pathogenic or likely pathogenic variant was identified in 54.7% of subjects (35/64). These variants fell within 27 genes previously associated with Mendelian disorders, including NSD1 and NFIX, which are known to be mutated in overgrowth syndromes.

CONCLUSION

We demonstrated that DNVs were enriched in chromatin remodelling (p=2×10^-4) and genes regulated by the fragile X mental retardation protein (p=3×10^-8), highlighting overlapping genetic mechanisms between MHID and related neurodevelopmental disorders.

Rare variants in the genetic background modulate cognitive and developmental phenotypes in individuals carrying disease-associated variants

Purpose

To assess the contribution of rare variants in the genetic background toward variability of neurodevelopmental phenotypes in individuals with rare copy-number variants (CNVs) and gene-disruptive variants.

Methods

We analyzed quantitative clinical information, exome sequencing, and microarray data from 757 probands and 233 parents and siblings who carry disease-associated variants.

Results

The number of rare likely deleterious variants in functionally intolerant genes (“other hits”) correlated with expression of neurodevelopmental phenotypes in probands with 16p12.1 deletion (n=23, p=0.004) and in autism probands carrying gene-disruptive variants (n=184, p=0.03) compared with their carrier family members. Probands with 16p12.1 deletion and a strong family history presented more severe clinical features (p=0.04) and higher burden of other hits compared with those with mild/no family history (p=0.001). The number of other hits also correlated with severity of cognitive impairment in probands carrying pathogenic CNVs (n=53) or de novo pathogenic variants in disease genes (n=290), and negatively correlated with head size among 80 probands with 16p11.2 deletion. These co-occurring hits involved known disease-associated genes such as SETD5, AUTS2, and NRXN1, and were enriched for cellular and developmental processes.

Conclusion

Accurate genetic diagnosis of complex disorders will require complete evaluation of the genetic background even after a candidate disease-associated variant is identified.

Whole-genome sequencing in patients with ciliopathies uncovers a novel recurrent tandem duplication in IFT140

Ciliopathies represent a wide spectrum of rare diseases with overlapping phenotypes and a high genetic heterogeneity. Among those, IFT140 is implicated in a variety of phenotypes ranging from isolated retinis pigmentosa to more syndromic cases. Using whole-genome sequencing in patients with uncharacterized ciliopathies, we identified a novel recurrent tandem duplication of exon 27-30 (6.7 kb) in IFT140, c.3454-488_4182+2588dup p.(Tyr1152_Thr1394dup), missed by whole-exome sequencing. Pathogenicity of the mutation was assessed on the patients' skin fibroblasts. Several hundreds of patients with a ciliopathy phenotype were screened and biallelic mutations were identified in 11 families representing 12 pathogenic variants of which seven are novel. Among those unrelated families especially with a Mainzer-Saldino syndrome, eight carried the same tandem duplication (two at the homozygous state and six at the heterozygous state). In conclusion, we demonstrated the implication of structural variations in IFT140-related diseases expanding its mutation spectrum. We also provide evidences for a unique genomic event mediated by an Alu-Alu recombination occurring on a shared haplotype. We confirm that whole-genome sequencing can be instrumental in the ability to detect structural variants for genomic disorders.

Further delineation of the MECP2 duplication syndrome phenotype in 59 French male patients, with a particular focus on morphological and neurological features

The Xq28 duplication involving the MECP2 gene (MECP2 duplication) has been mainly described in male patients with severe developmental delay (DD) associated with spasticity, stereotypic movements and recurrent infections. Nevertheless, only a few series have been published. We aimed to better describe the phenotype of this condition, with a focus on morphological and neurological features. Through a national collaborative study, we report a large French series of 59 affected males with interstitial MECP2 duplication. Most of the patients (93%) shared similar facial features, which evolved with age (midface hypoplasia, narrow and prominent nasal bridge, thick lower lip, large prominent ears), thick hair, livedo of the limbs, tapered fingers, small feet and vasomotor troubles. Early hypotonia and global DD were constant, with 21% of patients unable to walk. In patients able to stand, lower limbs weakness and spasticity led to a singular standing habitus: flexion of the knees, broad-based stance with pseudo-ataxic gait. Scoliosis was frequent (53%), such as divergent strabismus (76%) and hypermetropia (54%), stereotypic movements (89%), without obvious social withdrawal and decreased pain sensitivity (78%). Most of the patients did not develop expressive language, 35% saying few words. Epilepsy was frequent (59%), with a mean onset around 7.4 years of age, and often (62%) drug-resistant. Other medical issues were frequent: constipation (78%), and recurrent infections (89%), mainly lung. We delineate the clinical phenotype of MECP2 duplication syndrome in a large series of 59 males. Pulmonary hypertension appeared as a cause of early death in these patients, advocating its screening early in life.

Sex chromosome aneuploidies and copy-number variants: a further explanation for neurodevelopmental prognosis variability?

Sex chromosome aneuploidies (SCA) is a group of conditions in which individuals have an abnormal number of sex chromosomes. SCA, such as Klinefelter's syndrome, XYY syndrome, and Triple X syndrome are associated with a large range of neurological outcome. Another genetic event such as another cytogenetic abnormality may explain a part of this variable expressivity. In this study, we have recruited fourteen patients with intellectual disability or developmental delay carrying SCA associated with a copy-number variant (CNV). In our cohort (four patients 47,XXY, four patients 47,XXX, and six patients 47,XYY), seven patients were carrying a pathogenic CNV, two a likely pathogenic CNV and five a variant of uncertain significance. Our analysis suggests that CNV might be considered as an additional independent genetic factor for intellectual disability and developmental delay for patients with SCA and neurodevelopmental disorder.

Rare Inherited and De Novo CNVs Reveal Complex Contributions to ASD Risk in Multiplex Families

Rare mutations, including copy-number variants (CNVs), contribute significantly to autism spectrum disorder (ASD) risk. Although their importance has been established in families with only one affected child (simplex families), the contribution of both de novo and inherited CNVs to ASD in families with multiple affected individuals (multiplex families) is less well understood. We analyzed 1,532 families from the Autism Genetic Resource Exchange (AGRE) to assess the impact of de novo and rare CNVs on ASD risk in multiplex families. We observed a higher burden of large, rare CNVs, including inherited events, in individuals with ASD than in their unaffected siblings (odds ratio [OR] = 1.7), but the rate of de novo events was significantly lower than in simplex families. In previously characterized ASD risk loci, we identified 49 CNVs, comprising 24 inherited events, 19 de novo events, and 6 events of unknown inheritance, a significant enrichment in affected versus control individuals (OR = 3.3). In 21 of the 30 families (71%) in whom at least one affected sibling harbored an established ASD major risk CNV, including five families harboring inherited CNVs, the CNV was not shared by all affected siblings, indicating that other risk factors are contributing. We also identified a rare risk locus for ASD and language delay at chromosomal region 2q24 (implicating NR4A2) and another lower-penetrance locus involving inherited deletions and duplications of WWOX. The genetic architecture in multiplex families differs from that in simplex families and is complex, warranting more complete genetic characterization of larger multiplex ASD cohorts.

Karyotype is not dead (yet)!

BACKGROUND

While array-comparative genomic hybridization (a-CGH) and next-generation sequencing (NGS or exome) technologies have swiftly spread throughout the medical field, karyotype has gradually lost its leading role among genetic tests. Several international guidelines recommend starting with a-CGH screening then going on with exome analysis when investigating a patient with intellectual disability (ID) and no precise clinical diagnosis. A-CGH and whole exome sequencing increase etiologic diagnoses rate up to 30% in case of ID. However, physicians have to deal with the lack of qualitative information of the genome. Especially, exome and a-CGH analysis fail to detect chromosomal rearrangements because breakpoints are either located in introns or not associated with a gain or loss of genetic material. If these technologies cannot easily identify chromosomal translocations or inversions which sometimes split a gene, karyotype can.

DISCUSSION

For the 5 cases described, karyotype provided the right diagnosis for a Mendelian disease while molecular analysis remained unsuccessful. We conclude that when a Mendelian disease is strongly suggested clinically, if molecular analysis is normal, it could be very useful to carry out a karyotype in order to demonstrate a chromosomal rearrangement involving the targeted gene. If this gene is disrupted, the physician can confirm the suspected disease and give appropriate genetic counseling.

SUMMARY

This article aims at keeping in mind that karyotype, this old-fashioned genetic tool, can still remain powerful and useful within some genetic issues. Even in this modern period of whole exome sequencing, young geneticists should know that karyotype remains a powerful and cheap technology, available throughout the world and can still do a lot for families.

The expanding spectrum of COL2A1 gene variants IN 136 patients with a skeletal dysplasia phenotype

Heterozygous COL2A1 variants cause a wide spectrum of skeletal dysplasia termed type II collagenopathies. We assessed the impact of this gene in our French series. A decision tree was applied to select 136 probands (71 Stickler cases, 21 Spondyloepiphyseal dysplasia congenita cases, 11 Kniest dysplasia cases, and 34 other dysplasia cases) before molecular diagnosis by Sanger sequencing. We identified 66 different variants among the 71 positive patients. Among those patients, 18 belonged to multiplex families and 53 were sporadic. Most variants (38/44, 86%) were located in the triple helical domain of the collagen chain and glycine substitutions were mainly observed in severe phenotypes, whereas arginine to cysteine changes were more often encountered in moderate phenotypes. This series of skeletal dysplasia is one of the largest reported so far, adding 44 novel variants (15%) to published data. We have confirmed that about half of our Stickler patients (46%) carried a COL2A1 variant, and that the molecular spectrum was different across the phenotypes. To further address the question of genotype-phenotype correlation, we plan to screen our patients for other candidate genes using a targeted next-generation sequencing approach.

A French multicenter study of over 700 patients with 22q11 deletions diagnosed using FISH or aCGH

Although 22q11.2 deletion syndrome (22q11.2DS) is the most recurrent human microdeletion syndrome associated with a highly variable phenotype, little is known about the condition's true incidence and the phenotype at diagnosis. We performed a multicenter, retrospective analysis of postnatally diagnosed patients recruited by members of the Association des Cytogénéticiens de Langue Française (the French-Speaking Cytogeneticists Association). Clinical and cytogenetic data on 749 cases diagnosed between 1995 and 2013 were collected by 31 French cytogenetics laboratories. The most frequent reasons for referral of postnatally diagnosed cases were a congenital heart defect (CHD, 48.6%), facial dysmorphism (49.7%) and developmental delay (40.7%). Since 2007 (the year in which array comparative genomic hybridization (aCGH) was introduced for the routine screening of patients with intellectual disability), almost all cases have been diagnosed using FISH (96.1%). Only 15 cases (all with an atypical phenotype) were diagnosed with aCGH; the deletion size ranged from 745 to 2904 kb. The deletion was inherited in 15.0% of cases and was of maternal origin in 85.5% of the latter. This is the largest yet documented cohort of patients with 22q11.2DS (the most commonly diagnosed microdeletion) from the same population. French cytogenetics laboratories diagnosed at least 108 affected patients (including fetuses) per year from among a national population of ∼66 million. As observed for prenatal diagnoses, CHDs were the most frequently detected malformation in postnatal diagnoses. The most common CHD in postnatal diagnoses was an isolated septal defect.

Mutation Update of the CLCN5 Gene Responsible for Dent Disease 1

Dent disease is a rare X-linked tubulopathy characterized by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis and/or nephrolithiasis, progressive renal failure, and variable manifestations of other proximal tubule dysfunctions. It often progresses over a few decades to chronic renal insufficiency, and therefore molecular characterization is important to allow appropriate genetic counseling. Two genetic subtypes have been described to date: Dent disease 1 is caused by mutations of the CLCN5 gene, coding for the chloride/proton exchanger ClC-5; and Dent disease 2 by mutations of the OCRL gene, coding for the inositol polyphosphate 5-phosphatase OCRL-1. Herein, we review previously reported mutations (n = 192) and their associated phenotype in 377 male patients with Dent disease 1 and describe phenotype and novel (n = 42) and recurrent mutations (n = 24) in a large cohort of 117 Dent disease 1 patients belonging to 90 families. The novel missense and in-frame mutations described were mapped onto a three-dimensional homology model of the ClC-5 protein. This analysis suggests that these mutations affect the dimerization process, helix stability, or transport. The phenotype of our cohort patients supports and extends the phenotype that has been reported in smaller studies.

Efficient strategy for the molecular diagnosis of intellectual disability using targeted high-throughput sequencing

Background

Intellectual disability (ID) is characterised by an extreme genetic heterogeneity. Several hundred genes have been associated to monogenic forms of ID, considerably complicating molecular diagnostics. Trio-exome sequencing was recently proposed as a diagnostic approach, yet remains costly for a general implementation.

Methods

We report the alternative strategy of targeted high-throughput sequencing of 217 genes in which mutations had been reported in patients with ID or autism as the major clinical concern. We analysed 106 patients with ID of unknown aetiology following array-CGH analysis and other genetic investigations. Ninety per cent of these patients were males, and 75% sporadic cases.

Results

We identified 26 causative mutations: 16 in X-linked genes (ATRX, CUL4B, DMD, FMR1, HCFC1, IL1RAPL1, IQSEC2, KDM5C, MAOA, MECP2, SLC9A6, SLC16A2, PHF8) and 10 de novo in autosomal-dominant genes (DYRK1A, GRIN1, MED13L, TCF4, RAI1, SHANK3, SLC2A1, SYNGAP1). We also detected four possibly causative mutations (eg, in NLGN3) requiring further investigations. We present detailed reasoning for assigning causality for each mutation, and associated patients’ clinical information. Some genes were hit more than once in our cohort, suggesting they correspond to more frequent ID-associated conditions (KDM5C, MECP2, DYRK1A, TCF4). We highlight some unexpected genotype to phenotype correlations, with causative mutations being identified in genes associated to defined syndromes in patients deviating from the classic phenotype (DMD, TCF4, MECP2). We also bring additional supportive (HCFC1, MED13L) or unsupportive (SHROOM4, SRPX2) evidences for the implication of previous candidate genes or mutations in cognitive disorders.

Conclusions

With a diagnostic yield of 25% targeted sequencing appears relevant as a first intention test for the diagnosis of ID, but importantly will also contribute to a better understanding regarding the specific contribution of the many genes implicated in ID and autism.

Analysis of 339 pregnancies in 181 women with 13 different forms of inherited thrombocytopenia

Pregnancy in women with inherited thrombocytopenias is a major matter of concern as both the mothers and the newborns are potentially at risk of bleeding. However, medical management of this condition cannot be based on evidence because of the lack of consistent information in the literature. To advance knowledge on this matter, we performed a multicentric, retrospective study evaluating 339 pregnancies in 181 women with 13 different forms of inherited thrombocytopenia. Neither the degree of thrombocytopenia nor the severity of bleeding tendency worsened during pregnancy and the course of pregnancy did not differ from that of healthy subjects in terms of miscarriages, fetal bleeding and pre-term births. The degree of thrombocytopenia in the babies was similar to that in the mother. Only 7 of 156 affected newborns had delivery-related bleeding, but 2 of them died of cerebral hemorrhage. The frequency of delivery-related maternal bleeding ranged from 6.8% to 14.2% depending on the definition of abnormal blood loss, suggesting that the risk of abnormal blood loss was increased with respect to the general population. However, no mother died or had to undergo hysterectomy to arrest bleeding. The search for parameters predicting delivery-related bleeding in the mother suggested that hemorrhages requiring blood transfusion were more frequent in women with history of severe bleedings before pregnancy and with platelet count at delivery below 50 × 10(9)/L.

Molecular findings and clinical data in a cohort of 150 patients with anophthalmia/microphthalmia

Anophthalmia and microphthalmia (AM) are the most severe malformations of the eye, corresponding respectively to reduced size or absent ocular globe. Wide genetic heterogeneity has been reported and different genes have been demonstrated to be causative of syndromic and non-syndromic forms of AM. We screened seven AM genes [GDF6 (growth differentiation factor 6), FOXE3 (forkhead box E3), OTX2 (orthodenticle protein homolog 2), PAX6 (paired box 6), RAX (retina and anterior neural fold homeobox), SOX2 (SRY sex determining region Y-box 2), and VSX2 (visual system homeobox 2 gene)] in a cohort of 150 patients with isolated or syndromic AM. The causative genetic defect was identified in 21% of the patients (32/150). Point mutations were identified by direct sequencing of these genes in 25 patients (13 in SOX2, 4 in RAX, 3 in OTX2, 2 in FOXE3, 1 in VSX2, 1 in PAX6, and 1 in GDF6). In addition eight gene deletions (five SOX2, two OTX2 and one RAX) were identified using a semi-quantitative multiplex polymerase chain reaction (PCR) [quantitative multiplex PCR amplification of short fluorescent fragments (QMPSF)]. The causative genetic defect was identified in 21% of the patients. This result contributes to our knowledge of the molecular basis of AM, and will facilitate accurate genetic counselling.

Array-CGH Analysis Suggests Genetic Heterogeneity in Rhombencephalosynapsis

Rhombencephalosynapsis is an uncommon, but increasingly recognized, cerebellar malformation defined as vermian agenesis with fusion of the hemispheres. The embryologic and genetic mechanisms involved are still unknown, and to date, no animal models are available. In the present study, we used Agilent oligonucleotide arrays in a large series of 57 affected patients to detect candidate genes. Four different unbalanced rearrangements were detected: a 16p11.2 deletion, a 14q12q21.2 deletion, an unbalanced translocation t(2p;10q), and a 16p13.11 microdeletion containing 2 candidate genes. These genes were further investigated by sequencing and in situ hybridization. This first microarray screening of a rhombencephalosynapsis series suggests that there may be heterogeneous genetic causes.

Systematic molecular and cytogenetic screening of 100 patients with marfanoid syndromes and intellectual disability

The association of marfanoid habitus (MH) and intellectual disability (ID) has been reported in the literature, with overlapping presentations and genetic heterogeneity. A hundred patients (71 males and 29 females) with a MH and ID were recruited. Custom-designed 244K array-CGH (Agilent®; Agilent Technologies Inc., Santa Clara, CA) and MED12, ZDHHC9, UPF3B, FBN1, TGFBR1 and TGFBR2 sequencing analyses were performed. Eighty patients could be classified as isolated MH and ID: 12 chromosomal imbalances, 1 FBN1 mutation and 1 possibly pathogenic MED12 mutation were found (17%). Twenty patients could be classified as ID with other extra-skeletal features of the Marfan syndrome (MFS) spectrum: 4 pathogenic FBN1 mutations and 4 chromosomal imbalances were found (2 patients with both FBN1 mutation and chromosomal rearrangement) (29%). These results suggest either that there are more loci with genes yet to be discovered or that MH can also be a relatively non-specific feature of patients with ID. The search for aortic complications is mandatory even if MH is associated with ID since FBN1 mutations or rearrangements were found in some patients. The excess of males is in favour of the involvement of other X-linked genes. Although it was impossible to make a diagnosis in 80% of patients, these results will improve genetic counselling in families.

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.

Wilms' tumor in patients with 9q22.3 microdeletion syndrome suggests a role for PTCH1 in nephroblastomas

Nephroblastoma (Wilms' tumor; WT) is the most common renal tumor of childhood. To date, several genetic abnormalities predisposing to WT have been identified in rare overgrowth syndromes. Among them, abnormal methylation of the 11p15 region, GPC3 and DIS3L2 mutations, which are responsible for Beckwith-Wiedemann, Simpson-Golabi-Behmel and Perlman syndromes, respectively. However, the underlying cause of WT remains unknown in the majority of cases. We report three unrelated patients who presented with WT in addition to a constitutional 9q22.3 microdeletion and dysmorphic/overgrowth syndrome. The size of the deletions was variable (ie, from 1.7 to 8.9 Mb) but invariably encompassed the PTCH1 gene. Subsequently, we identified a somatic PTCH1 nonsense mutation in the renal tumor of one patient. In addition, by array comparative genomic hybridization method, we analyzed the DNA extracted from the blood samples of nine patients with overgrowth syndrome and WT, but did not identify any deleterious chromosomal imbalances in these patients. These findings strongly suggest that patients with constitutional 9q22.3 microdeletion have an increased risk of WT, and that PTCH1 have a role in the pathogenesis of nephroblastomas.

NEK1 and DYNC2H1 are both involved in short rib polydactyly Majewski type but not in Beemer Langer cases

BACKGROUND

The lethal short rib polydactyly syndromes (SRP type I-IV) are characterised by notably short ribs, short limbs, polydactyly, multiple anomalies of major organs, and autosomal recessive mode of inheritance. Among them, SRP type II (Majewski; MIM 263520) is characterised by short ovoid tibiae or tibial agenesis and is radiographically closely related to SRP type IV (Beemer-Langer; MIM 269860) which is distinguished by bowed radii and ulnae and relatively well tubulated tibiae. NEK1 mutations have been recently identified in SRP type II. Double heterozygosity for mutations in both NEK1 and DYNC2H1 in one SRP type II case supported possible digenic diallelic inheritance.

METHODS

The aim of this study was to screen DYNC2H1 and NEK1 in 13 SRP type II cases and seven SRP type IV cases. It was not possible to screen DYNC2H1 in two patients due to insufficient amount of DNA.

RESULTS

The study identified homozygous NEK1 mutations in 5/13 SRP type II and compound heterozygous DYNC2H1 mutations in 4/12 cases. Finally, NEK1 and DYNC2H1 were excluded in 3/12 SRP type II and in all SRP type IV cases. The main difference between the mutation positive SRP type II group and the mutation negative SRP type II group was the presence of holoprosencephaly and polymycrogyria in the mutation negative group.

CONCLUSION

This study confirms that NEK1 is one gene causing SRP type II but also reports mutations in DYNC2H1, expanding the phenotypic spectrum of DYNC2H1 mutations. The exclusion of NEK1 and DYNC2H1 in 3/12 SRP type II and in all SRP type IV cases further support genetic heterogeneity.

OTX2 mutations contribute to the otocephaly-dysgnathia complex

BACKGROUND

Otocephaly or dysgnathia complex is characterised by mandibular hypoplasia/agenesis, ear anomalies, microstomia, and microglossia; the molecular basis of this developmental defect is largely unknown in humans.

METHODS AND RESULTS

This study reports a large family in which two cousins with micro/anophthalmia each gave birth to at least one child with otocephaly, suggesting a genetic relationship between anophthalmia and otocephaly. OTX2, a known microphthalmia locus, was screened in this family and a frameshifting mutation was found. The study subsequently identified in one unrelated otocephalic patient a sporadic OTX2 mutation. Because OTX2 mutations may not be sufficient to cause otocephaly, the study assayed the potential of otx2 to modify craniofacial phenotypes in the context of known otocephaly gene suppression in vivo. It was found that otx2 can interact genetically with pgap1, prrx1, and msx1 to exacerbate mandibular and midline defects during zebrafish development. However, sequencing of these loci in the OTX2-positive families did not unearth likely pathogenic lesions, suggesting further genetic heterogeneity and complexity.

CONCLUSION

Identification of OTX2 involvement in otocephaly/dysgnathia in humans, even if loss of function mutations at this locus does not sufficiently explain the complex anatomical defects of these patients, suggests the requirement for a second genetic hit. Consistent with this notion, trans suppression of otx2 and other developmentally related genes recapitulate aspects of the otocephaly phenotype in zebrafish. This study highlights the combined utility of genetics and functional approaches to dissect both the regulatory pathways that govern craniofacial development and the genetics of this disease group.

Clinical and molecular characterization of 17q21.31 microdeletion syndrome in 14 French patients with mental retardation

Chromosome 17q21.31 microdeletion was one of the first genomic disorders identified by chromosome microarrays. We report here the clinical and molecular characterization of a new series of 14 French patients with this microdeletion syndrome. The most frequent clinical features were hypotonia, developmental delay and facial dysmorphism, but scaphocephaly, prenatal ischemic infarction and perception deafness were also described. Genotyping of the parents showed that the parent from which the abnormality was inherited carried the H2 inversion polymorphism, confirming that the H2 allele is necessary, but not sufficient to generate the 17q21.31 microdeletion. Previously reported molecular analyses of patients with 17q21.31 microdeletion syndrome defined a 493 kb genomic fragment that was deleted in most patients after taking into account frequent copy number variations in normal controls, but the deleted interval was significantly smaller (205 kb) in one of our patients, encompassing only the MAPT, STH and KIAA1267 genes. As this patient presents the classical phenotype of 17q21.31 syndrome, these data make it possible to define a new minimal critical region of 160.8 kb, strengthening the evidence for involvement of the MAPT gene in this syndrome.

Mutation update for the CSB/ERCC6 and CSA/ERCC8 genes involved in Cockayne syndrome

Cockayne syndrome is an autosomal recessive multisystem disorder characterized principally by neurological and sensory impairment, cachectic dwarfism, and photosensitivity. This rare disease is linked to mutations in the CSB/ERCC6 and CSA/ERCC8 genes encoding proteins involved in the transcription-coupled DNA repair pathway. The clinical spectrum of Cockayne syndrome encompasses a wide range of severity from severe prenatal forms to mild and late-onset presentations. We have reviewed the 45 published mutations in CSA and CSB to date and we report 43 new mutations in these genes together with the corresponding clinical data. Among the 84 reported kindreds, 52 (62%) have mutations in the CSB gene. Many types of mutations are scattered along the whole coding sequence of both genes, but clusters of missense mutations can be recognized and highlight the role of particular motifs in the proteins. Genotype-phenotype correlation hypotheses are considered with regard to these new molecular and clinical data. Additional cases of molecular prenatal diagnosis are reported and the strategy for prenatal testing is discussed. Two web-based locus-specific databases have been created to list all identified variants and to allow the inclusion of future reports (www.umd.be/CSA/ and www.umd.be/CSB/).

Identification of gene copy number variations in patients with mental retardation using array-CGH: Novel syndromes in a large French series

Array-CGH has revealed a large number of copy number variations (CNVs) in patients with multiple congenital anomalies and/or mental retardation (MCA/MR). According to criteria recently listed, pathogenicity was clearly suspected for some CNVs but benign CNVs, considered as polymorphisms, have complicated the interpretation of the results. In this study, genomic DNAs from 132 French patients with unexplained mental retardation were analysed by genome wide high-resolution Agilent 44K oligonucleotide arrays. The results were in accordance with those observed in previous studies: the detection rate of pathogenic CNVs was 14.4%. A non-random involvement of several chromosomal regions was observed. Some of the microimbalances recurrently involved regions (1q21.1, 2q23.1, 2q32q33, 7p13, 17p13.3, 17p11.2, 17q21.31) corresponding to known or novel syndromes. For all the pathogenic CNVs, further cases are needed to allow more accurate genotype-phenotype correlations underscoring the importance of databases to group patients with similar molecular data.

Familial frameshift SRY mutation inherited from a mosaic father with testicular dysgenesis syndrome

CONTEXT

The SRY gene encodes a transcription factor responsible for initiating testis differentiation. Mutations in SRY almost always result in XY sex reversal with pure gonadal dysgenesis and an increased risk of gonadal tumor. Most of these mutations are de novo, affecting only one individual in a family. Only a small subset of mutations is shared between a phenotypically normal father and one or more of his affected children. Incomplete penetrance and somatic mosaicism are two hypotheses that may explain a normal phenotype in a father carrying a SRY mutation.

PATIENTS AND RESULTS

We describe a family with two sisters with XY sex reversal and pure gonadal dysgenesis and a phenotypically normal brother. A novel constitutional frameshift SRY mutation was identified in both sisters and was absent in the brother. The single base pair deletion (c.71delA) led to a premature stop codon in position 60 of the protein, removing entirely the high-mobility group domain and the DNA-binding domain of SRY. The father of the three children presented with hypospadias; cryptorchidism; testicular seminoma and oligoasthenozoospermia, an association termed testicular dysgenesis syndrome (TDS); and the SRY mutation in a mosaic state in the peripheral blood and the tumor.

CONCLUSIONS

This observation of somatic and germinal mosaicism for a SRY mutation may explain the variable penetrance in some familial gonadal dysgenesis. Importantly, the present report is the first one describing the association of SRY mutation in a male with TDS. This suggests that mutations in a sex-determining gene may contribute to the pathogenesis of TDS.

Molecular analysis of pericentrin gene (PCNT) in a series of 24 Seckel/microcephalic osteodysplastic primordial dwarfism type II (MOPD II) families

Microcephalic osteodysplastic primordial dwarfism type II (MOPD II, MIM 210720) and Seckel syndrome (SCKL, MIM 210600) belong to the primordial dwarfism group characterised by intrauterine growth retardation, severe proportionate short stature, and pronounced microcephaly. MOPD II is distinct from SCKL by more severe growth retardation, radiological abnormalities, and absent or mild mental retardation. Seckel syndrome is associated with defective ATR dependent DNA damage signalling. In 2008, loss-of-function mutations in the pericentrin gene (PCNT) have been identified in 28 patients, including 3 SCKL and 25 MOPDII cases. This gene encodes a centrosomal protein which plays a key role in the organisation of mitotic spindles. The aim of this study was to analyse PCNT in a large series of SCKL-MOPD II cases to further define the clinical spectrum associated with PCNT mutations. Among 18 consanguineous families (13 SCKL and 5 MOPDII) and 6 isolated cases (3 SCKL and 3 MOPD II), 13 distinct mutations were identified in 5/16 SCKL and 8/8 MOPDII including five stop mutations, five frameshift mutations, two splice site mutations, and one apparent missense mutation affecting the last base of exon 19. Moreover, we demonstrated that this latter mutation leads to an abnormal splicing with a predicted premature termination of translation. The clinical analysis of the 5 SCKL cases with PCNT mutations showed that they all presented minor skeletal changes and clinical features compatible with MOPDII diagnosis. It is therefore concluded that, despite variable severity, MOPDII is a genetically homogeneous condition due to loss-of-function of pericentrin.

TCF4 deletions in Pitt-Hopkins Syndrome

Pitt-Hopkins syndrome (PHS) is a probably underdiagnosed, syndromic mental retardation disorder, marked by hyperventilation episodes and characteristic dysmorphism (large beaked nose, wide mouth, fleshy lips, and clubbed fingertips). PHS was shown to be caused by de novo heterozygous mutations of the TCF4 gene, located in 18q21. We selected for this study 30 unrelated patients whose phenotype overlapped PHS but which had been initially addressed for Angelman, Mowat-Wilson, or Rett syndromes. In 10 patients we identified nine novel mutations (four large cryptic deletions, including one in mosaic, and five small deletions), and a recurrent one. So far, a total of 20 different TCF4 gene mutations have been reported, most of which either consist in deletion of significant portions of the TCF4 coding sequence, or generate premature stop codons. No obvious departure was observed between the patients harboring point mutations and large deletions at the 18q21 locus, further supporting TCF4 haploinsufficiency as the molecular mechanism underling PHS. In this report, we also further specify the phenotypic spectrum of PHS, enlarged to behavior, with aim to increase the rate and specificity of PHS diagnosis.

Cerebro-oculo-facio-skeletal syndrome: three additional cases with CSB mutations, new diagnostic criteria and an approach to investigation

BACKGROUND

The cerebro-oculo-facio-skeletal syndrome (COFS syndrome) is an autosomal recessive disorder which was initially described in a specific aboriginal population from Manitoba. In recent years, COFS syndrome has been linked in this original population to a defective DNA repair pathway and to a homozygous mutation in the major gene underlying Cockayne syndrome (CSB). However, most reports of suspected COFS syndrome outside this population have not been confirmed at the molecular level, leading to considerable heterogeneity within the syndrome and confusing overlaps between COFS syndrome and other eye and brain disorders.

OBJECTIVE

To refine the delineation of the syndrome on genetically proven COFS cases.

METHODS

We report the exhaustive clinical, cellular and molecular data of three unrelated COFS patients with mutations in the CSB gene.

RESULTS

All three patients present the cardinal features of COFS syndrome including extreme microcephaly, congenital cataracts, facial dysmorphism and arthrogryposis. They also exhibit a predominantly postnatal growth failure, a severe psychomotor retardation, with axial hypotonia and peripheral hypertonia and neonatal feeding difficulties. Fibroblasts from the patients show the same DNA repair defect which can be complemented by transfection of the CSB wild-type cDNA. Five new mutations in the CSB gene have been identified in these patients.

CONCLUSIONS

Our data indicate that COFS syndrome represents the most severe end of the Cockayne spectrum. New diagnostic criteria for COFS syndrome are proposed, based on our findings and on the few genetically proven COFS cases from the literature.

A new mutation in TP63 is associated with age-related pathology

Increases in the number of allelic malformation syndromes have led to their classification according to their pathogenesis rather than their clinical specific phenotype. TP63 (also known as TP73L) mutations have been identified in several such syndromes characterized by autosomal dominant transmission and various combinations of ectodermal dysplasia, limb malformations and orofacial clefting. TP63 has not yet been implicated in early aging phenotype in humans, even though p63 activates a program of cellular senescence and p63-compromised mice display features of accelerated aging. We report on a family with four affected adult females presenting with Rapp-Hodgkin syndrome (RHS), an autosomal dominant clinical entity that associates anhidrotic ectodermal dysplasia with cleft lip and palate. Features between RHS and EEC syndrome (ectrodactyly, ectodermal dysplasia and cleft lip/palate) have led to the recent identification of mutations in the TP63 gene, located on 3q27, in this condition. Our patients present typical clinical features of RHS, but also ophthalmic anomalies such as corneal dystrophy and premature menopause (around 30 years). The latter findings have never been reported in this condition, and could be secondary to a new TP63 deletion that has been identified in this family.

Testing for triallelism: analysis of six BBS genes in a Bardet–Biedl syndrome family cohort

The phenotype of Bardet-Biedl syndrome (BBS) is defined by the association of retinitis pigmentosa, obesity, polydactyly, hypogenitalism, renal disease and cognitive impairement. The significant genetic heterogeneity of this condition is supported by the identification, to date, of eight genes (BBS1-8) implied with cilia assembly or function. Triallelic inheritance has recently been suggested on the basis of the identification of three mutated alleles in two different genes for the same patient. In a cohort of 27 families, six BBS genes (namely BBS1, BBS2, BBS4, BBS6, BBS7 and BBS8) have been studied. Mutations were identified in 14 families. Two mutations within the same gene have been identified in seven families. BBS1 is most frequently implied with the common M390R substitution at the homozygous state (n=2), or associated with another mutation at BBS1 (n=3). Compound heterozygous mutations have been found in BBS2 (one family) and BBS6 (one family). In seven other families, only one heterozygous mutation has been identified (once in BBS1, twice for BBS2 and three times in BBS6). Although our study did not reveal any families with bona fide mutations in two BBS genes, consistent with a triallelic hypothesis, we have found an excess of heterozygous single mutations. This study underlines the genetic heterogeneity of the BBS and the involvement of possibly unidentified genes.

Complete exon-intron structure of the RPGR-interacting protein (RPGRIP1) gene allows the identification of mutations underlying Leber congenital amaurosis

Leber congenital amaurosis (LCA) is a genetically heterogeneous autosomal recessive condition responsible for congenital blindness or greatly impaired vision since birth. So far, six LCA loci have been mapped but only 4 out of 6 genes have been identified. A genome-wide screen for homozygosity was conducted in seven consanguineous families unlinked to any of the six LCA loci. Evidence for homozygosity was found in two of these seven families at the 14q11 chromosomal region. Two retinal specific candidate genes were known to map to this region, namely the neural retina leucine zipper (NRL) and the retinitis pigmentosa GTPase regulator interacting protein (RPGRIP1). No mutation of the NRL gene was found in any of the two families. Thus, we determined the complete exon-intron structure of the RPGRIP1 gene. RPGRIP1 encompasses 24 coding exons, nine of which are first described here with their corresponding exon-intron boundaries. The screening of the gene in the two families consistent with linkage to chromosome 14q11 allowed the identification of a homozygous null mutation and a homozygous missense mutation, respectively. Further screening of LCA patients unlinked to any of the four already identified LCA genes (n=86) identified seven additional mutations in six of them. In total, eight distinct mutations (5 out of 8 truncating) in 8/93 patients were found. So far this gene accounts for eight out of 142 LCA cases in our series (5.6%).

A second family with XLRH displays the mutation S244L in the CLCN5 gene

Mutations in the CLCN5 gene, mapped in Xp11.22, have been recently reported to be associated with X-linked nephrolithiasis, X-linked recessive hypophosphataemic rickets and Dent's disease. We report a missense mutation in exon 6 of the CLCN5 gene. The mutation in this pedigree is S244L, the same mutation as has previously been described in an Italian family showing a similar pathology. However, in the family reported here, affected males have developed neither nephrolithiasis nor nephrocalcinosis. The question arises whether we are dealing with a milder phenotype or whether a more severe pathology will develop with ageing.