Truncating variants of the DLG4 gene are responsible for intellectual disability with marfanoid features.

Marfanoid habitus (MH) combined with intellectual disability (ID) is a genetically and clinically heterogeneous group of overlapping disorders. We performed exome sequencing in 33 trios and 31 single probands to identify novel genes specific to MH-ID. After the search for variants in known disease-causing genes and non-disease-causing genes with classical approaches, we searched for variants in non-disease-causing genes whose pLI was above 0.9 (ExAC Consortium data), in which truncating variants were found in at least 3 unrelated patients. Only DLG4 gene met these criteria. Data from the literature and various databases also indicated its implication in ID. DLG4 encodes post-synaptic density protein 95 (PSD-95), a protein expressed in various tissues, including the brain. In neurons, PSD-95 is located at the post-synaptic density, and is associated with glutamatergic receptor signaling (NMDA and AMPA). PSD-95 probably participates in dendritogenesis. Two patients were heterozygous for de novo frameshift variants and one patient carried a a consensus splice site variant. Gene expression studies supported their pathogenicity through haploinsufficiency and loss-of-function. Patients exhibited mild-to-moderate ID, similar marfanoid features, including a long face, high-arched palate, long and thin fingers, pectus excavatum, scoliosis and ophthalmological manifestations (nystagmus or strabismus). Our study emphasizes the role of DLG4 as a novel post-synaptic-associated gene involved in syndromic ID associated with MH.

Further delineation of a rare recessive encephalomyopathy linked to mutations in GFER thanks to data sharing of whole exome sequencing data.

BACKGROUND: Alterations in GFER gene have been associated with progressive mitochondrial myopathy, congenital cataracts, hearing loss, developmental delay, lactic acidosis and respiratory chain deficiency in 3 siblings born to consanguineous Moroccan parents by homozygosity mapping and candidate gene approach (OMIM#613076). Next generation sequencing recently confirmed this association by the finding of compound heterozygous variants in 19-year-old girl with a strikingly similar phenotype, but this ultra-rare entity remains however unknown from most of the scientific community. MATERIALS AND METHODS: Whole exome sequencing was performed as part of a "diagnostic odyssey" for suspected mitochondrial condition in 2 patients, presenting congenital cataracts, progressive encephalomyopathy and hypotrophy and detected unreported compound heterozygous variants in GFER. RESULTS: Thanks to an international data sharing, we found 2 additional patients carrying compound heterozygous variants in GFER. Reverse phenotyping confirmed the phenotypical similarities between the 4 patients. Together with the first literature reports, the review of these 8 cases from 4 unrelated families enables us to better describe this apparently homogeneous disorder, with the clinical and biological stigmata of mitochondrial disease. CONCLUSION: This report highlights the clinical utility of whole exome sequencing and reverse phenotyping for the diagnosis of ultra-rare diseases and underlines the importance of a broad data sharing for accurate clinical delineation of previously unrecognized entities.

Homozygous 16p13.11 duplication associated with mild intellectual disability and urinary tract malformations in two siblings born from consanguineous parents.

The use of array-comparative genomic hybridization (array-CGH) in routine clinical work has allowed the identification of many new copy number variations (CNV). The 16p13.11 duplication has been implicated in various congenital anomalies and neurodevelopmental disorders, but it has also been identified in healthy individuals. We report a clinical observation of two brothers from related parents each carrying a homozygous 16p13.11 duplication. The propositus had mild intellectual disability and posterior urethral valves with chronic renal disease. His brother was considered a healthy child with only learning disabilities and poor academic performances. However, a routine medical examination at 25-years-old revealed a mild chronic renal disease and ureteropelvic junction obstruction. Furthermore, the father presented with a unilateral renal agenesis, thus it seemed that a "congenital anomalies of kidney and urinary tract" (CAKUT) phenotype segregated in this family. This may be related to the duplication, but we cannot exclude the involvement of additional genetic or non-genetic factors in the urological phenotype. Several cohort studies showed association between this chromosomal imbalance and different clinical manifestations, but rarely with CAKUT. The duplication reported here was similar to the larger one of 3.4 Mb previously described versus the more common of 1.6 Mb. It encompassed at least 11 known genes, including the five ohnologs previously identified. Our observation, in addition to expanding the clinical spectrum of the duplication provides further support to understanding the underlying pathogenic mechanism.