M. Delrue

Gain-of-Function Mutations in RARB Cause Intellectual Disability with Progressive Motor Impairment

Retinoic acid (RA) signaling plays a key role in the development and function of several systems in mammals. We previously discovered that the de novo mutations c.1159C>T (p.Arg387Cys) and c.1159C>A (p.Arg387Ser) in the RA Receptor Beta (RARB) gene cause microphthalmia and diaphragmatic hernia. However, the natural history of affected subjects beyond the prenatal or neonatal period was unknown. Here, we describe nine additional subjects with microphthalmia who have de novo mutations in RARB, including the previously described p.Arg387Cys as well as the novel c.887G>C (p.Gly296Ala) and c.638T>C (p.Leu213Pro). Moreover, we review the information on four previously reported cases. All subjects who survived the neonatal period (n = 10) displayed severe global developmental delay with progressive motor impairment due to spasticity and/or dystonia (with or without chorea). The majority of subjects also showed Chiari type I malformation and severe feeding difficulties. We previously found that p.Arg387Cys and p.Arg387Ser induce a gain‐of‐function. We show here that the p.Gly296Ala and p.Leu213Pro RARB mutations further promote the RA ligand‐induced transcriptional activity by twofold to threefold over the wild‐type receptor, also indicating a gain‐of‐function mechanism. These observations suggest that precise regulation of RA signaling is required for brain development and/or function in humans.

Genomic study of severe fetal anomalies and discovery of GREB1L mutations in renal agenesis

PurposeFetal anomalies represent a poorly studied group of developmental disorders. Our objective was to assess the impact of whole-exome sequencing (WES) on the investigation of these anomalies.MethodsWe performed WES in 101 fetuses or stillborns who presented prenatally with severe anomalies, including renal a/dysgenesis, VACTERL association (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities), brain anomalies, suspected ciliopathies, multiple major malformations, and akinesia.ResultsA molecular diagnosis was obtained in 19 cases (19%). In 13 of these cases, the diagnosis was not initially suspected by the clinicians because the phenotype was nonspecific or atypical, corresponding in some cases to the severe end of the spectrum of a known disease (e.g., MNX1-, RYR1-, or TUBB-related disorders). In addition, we identified likely pathogenic variants in genes (DSTYK, ACTB, and HIVEP2) previously associated with phenotypes that were substantially different from those found in our cases. Finally, we identified variants in novel candidate genes that were associated with perinatal lethality, including de novo mutations in GREB1L in two cases with bilateral renal agenesis, which represents a significant enrichment of such mutations in our cohort.ConclusionOur study opens a window on the distinctive genetic landscape associated with fetal anomalies and highlights the power—but also the challenges—of WES in prenatal diagnosis.

A case of familial transmission of the newly described DNMT3A-Overgrowth Syndrome

DNMT3A‐Overgrowth Syndrome (also known as Tatton–Brown–Rahman Syndrome) (MIM 615879) has recently been described in 13 individuals with de novo heterozygous mutations in DNMT3A gene. This autosomal dominant condition is characterized by overgrowth, dysmorphic facial features and moderate intellectual disability. Missense and truncating point mutations, a small in‐frame deletion, as well as microdeletion 2p23 have been reported. Moreover, DNMT3A is commonly somatically mutated in acute myeloid leukemia. We herein report a family with two siblings and their father affected by the syndrome. The proband is a 12 year‐old boy with tall stature, macrocephaly, facial dysmorphism, and intellectual disability. His 10‐year‐old sister also has learning difficulties, overgrowth and mild facial dysmorphism. Their father is a 49 year‐old man with tall stature, macrocephaly, learning difficulties, and minor facial dysmorphism. He had a right occipital osteoma removed at 20 years of age. A heterozygous splice site mutation NM_022552.4 (DNMT3A): c.2323‐2A > T was found in the proband by whole exome sequencing analysis and by targeted Sanger Sequencing for the probands sister and father. This mutation has not been previously reported and is believed to be pathogenic. Indeed, this substitution involves a highly conserved canonical splice site and is predicted to cause exon skipping. This is the first report of a familial transmission of DNMT3A‐Overgrowth Syndrome, supporting the autosomal dominant inheritance. The probands phenotype is more severe than that of his two other affected family members, which illustrates variable expressivity in the syndrome.