A pathogenic CtBP1 missense mutation causes altered cofactor binding and transcriptional activity.

We previously reported a pathogenic de novo p.R342W mutation in the transcriptional corepressor CTBP1 in four independent patients with neurodevelopmental disabilities [1]. Here, we report the clinical phenotypes of seven additional individuals with the same recurrent de novo CTBP1 mutation. Within this cohort, we identified consistent CtBP1-related phenotypes of intellectual disability, ataxia, hypotonia, and tooth enamel defects present in most patients. The R342W mutation in CtBP1 is located within a region implicated in a high affinity-binding cleft for CtBP-interacting proteins. Unbiased proteomic analysis demonstrated reduced interaction of several chromatin-modifying factors with the CtBP1 W342 mutant. Genome-wide transcriptome analysis in human glioblastoma cell lines expressing -CtBP1 R342 (wt) or W342 mutation revealed changes in the expression profiles of genes controlling multiple cellular processes. Patient-derived dermal fibroblasts were found to be more sensitive to apoptosis during acute glucose deprivation compared to controls. Glucose deprivation strongly activated the BH3-only pro-apoptotic gene NOXA, suggesting a link between enhanced cell death and NOXA expression in patient fibroblasts. Our results suggest that context-dependent relief of transcriptional repression of the CtBP1 mutant W342 allele may contribute to deregulation of apoptosis in target tissues of patients leading to neurodevelopmental phenotypes.

A recurrent de novo CTBP1 mutation is associated with developmental delay, hypotonia, ataxia, and tooth enamel defects.

Exome sequencing is an effective way to identify genetic causes of etiologically heterogeneous conditions such as developmental delay and intellectual disabilities. Using exome sequencing, we have identified four patients with similar phenotypes of developmental delay, intellectual disability, failure to thrive, hypotonia, ataxia, and tooth enamel defects who all have the same de novo R331W missense variant in C-terminal binding protein 1 (CTBP1). CTBP1 is a transcriptional regulator critical for development by coordinating different regulatory pathways. The R331W variant found in these patients is within the C-terminal portion of the PLDLS (Pro-Leu-Asp-Leu-Ser) binding cleft, which is the domain through which CTBP1, interacts with chromatin-modifying enzymes and mediates chromatin-dependent gene repression pathways. This is the first report of mutations within CTBP1 in association with any human disease.

Expanding the spectrum of microdeletion 4q21 syndrome: a partial phenotype with incomplete deletion of the minimal critical region and a new association with cleft palate and Pierre Robin sequence.

Microdeletion 4q21 syndrome has been described in about a dozen patients with deletions ranging from 3.2 to 15.1 MB with similar features including the distinctive facial characteristics of broad forehead, hypertelorism, and prominent front teeth, with severe growth delay, developmental delay, and neonatal hypotonia. A 1.37 MB minimal critical region has been described that accounts for this shared phenotype and includes five known genes: PRKG2, RASGEF1B, HNRNPD, HNRPDL, and ENOPH1. We report on two new patients found through single nucleotide polymorphism (SNP) microarray testing that expand the reported phenotype. Patient 1 has a novel deletion of 2.0 MB, the smallest reported deletion, which involves only a partial deletion of the minimal critical region, including the genes HNRNPD, HNRPDL, and ENOPH1. She shares much of the typical phenotype including moderate developmental delay, unusual facial features, small hands and feet, but not any growth delay or neonatal hypotonia. This patient allows further genotype-phenotype correlation of the genes in the minimal critical region, and supports that heterozygous loss of PRKG2 leads to the growth delay. Patient 2 has a novel 3.4 MB deletion that includes the entire critical region, and has typical features, but also presented with cleft palate and Pierre Robin sequence, which have not been previously described. A gene reported to be associated with inherited cleft palate, SCD5, is in the deleted region in this patient, which suggests it may be playing a role in palate formation. Taken together, these patients allow for an expansion of the microdeletion 4q21 syndrome and provide candidate genes for particular features of the phenotype.

Paternal deletion 6q24.3: a new congenital anomaly syndrome associated with intrauterine growth failure, early developmental delay and characteristic facial appearance.

Deletions of the long arm of chromosome 6 are relatively uncommon and to date minimal genotype-phenotype correlations have been observed. We report on three unrelated patients with de novo paternal interstitial deletions of 6q24.3. FISH mapping was used to delineate the minimal region of overlap between these three patients. Although all three patients had different size deletions and different breakpoints, two of the patients shared a 2.5 Mb region of overlap and strikingly similar facial features including a triangular face, frontal bossing with metopic prominence, short and upward-slanting palpebral fissures, asymmetry of upper eyelids, hooded eyelids, shallow orbits, prominent inferior orbital crease, wide mouth, and long and flat philtrum. They also had redundant skin, joint laxity, a small thorax, and early developmental delay. The smallest region of overlap between all three patients was a region of deletion less than 1 Mb; all had a history of IUGR and postnatal short stature without overt radiologic skeletal anomalies. The dysmorphic features, early developmental and growth delay may be due to the hemizygous state for one of the genes in the deleted region of two of the patients or to a long range effect of the deletion on expression of other genes. In addition, since imprinted genes have been reported in this region, paternal deletion of an imprinted gene in all three patients may contribute to the growth phenotype. We propose that this is a new congenital malformation syndrome associated with a paternal deletion of 6q24.3.