MEF2C Haploinsufficiency features consistent hyperkinesis, variable epilepsy, and has a role in dorsal and ventral neuronal developmental pathways.

MEF2C haploinsufficiency syndrome is an emerging neurodevelopmental disorder associated with intellectual disability, autistic features, epilepsy, and abnormal movements. We report 16 new patients with MEF2C haploinsufficiency, including the oldest reported patient with MEF2C deletion at 5q14.3. We detail the neurobehavioral phenotype, epilepsy, and abnormal movements, and compare our subjects with those previously reported in the literature. We also investigate Mef2c expression in the developing mouse forebrain. A spectrum of neurofunctional deficits emerges, with hyperkinesis a consistent finding. Epilepsy varied from absent to severe, and included intractable myoclonic seizures and infantile spasms. Subjects with partial MEF2C deletion were statistically less likely to have epilepsy. Finally, we confirm that Mef2c is present both in dorsal primary neuroblasts and ventral gamma-aminobutyric acid(GABA)ergic interneurons in the forebrain of the developing mouse. Given interactions with several key neurodevelopmental genes such as ARX, FMR1, MECP2, and TBR1, it appears that MEF2C plays a role in several developmental stages of both dorsal and ventral neuronal cell types.

The intronic BRCA1 c.5407-25T>A variant causing partly skipping of exon 23-a likely pathogenic variant with reduced penetrance?

Rare sequence variants in the non-coding part of the BRCA genes are often reported as variants of uncertain significance (VUS), which leave patients and doctors in a challenging position. The aim of this study was to determine the pathogenicity of the BRCA1 c.5407-25T>A variant found in 20 families from Norway, France and United States with suspected hereditary breast and ovarian cancer. This was done by combining clinical and family information with allele frequency data, and assessment of the variant's effect on mRNA splicing. Mean age at breast (n = 12) and ovarian (n = 11) cancer diagnosis in female carriers was 49.9 and 60.4 years, respectively. The mean Manchester score in the 20 families was 16.4. The allele frequency of BRCA1 c.5407-25T>A was 1/64,566 in non-Finnish Europeans (gnomAD database v2.1.1). We found the variant in 1/400 anonymous Norwegian blood donors and 0/784 in-house exomes. Sequencing of patient-derived cDNA from blood, normal breast and ovarian tissue showed that BRCA1 c.5407-25T>A leads to skipping of exon 23, resulting in frameshift and protein truncation: p.(Gly1803GlnfsTer11). Western blot analysis of transiently expressed BRCA1 proteins in HeLa cells showed a reduced amount of the truncated protein compared with wild type. Noteworthily, we found that a small amount of full-length transcript was also generated from the c.5407-25T>A allele, potentially explaining the intermediate cancer burden in families carrying this variant. In summary, our results show that BRCA1 c.5407-25T>A leads to partial skipping of exon 23, and could represent a likely pathogenic variant with reduced penetrance.

Isolated Sagittal Synostosis in a Boy with Craniofrontonasal Dysplasia and a Novel EFNB1 Mutation.

Craniofrontonasal syndrome (CFNS) is a rare X-linked disorder that shows greater severity in females and is largely attributed to mutations in EFNB1. A 7-year-old boy presented with hypertelorism, broad nasal root, midfacial hypoplasia, mandibular prognathia, ptosis, and scaphocephaly was clinically diagnosed with CFNS. Three-dimensional computed tomographic scans confirmed the isolated sagittal synostosis. His mother also showed clinical features of CFNS, but less severe. Genetic tests uncovered a novel C to T mutation at nucleotide 466 (c.466C>T) in exon 1 of EFNB1 for both. To the best of our knowledge, this is the only reported incident of CFNS in a male child exhibiting isolated sagittal synostosis.

Novel mutation in MYH7 gene associated with distal myopathy and cardiomyopathy.

A 25-year-old woman had childhood-onset muscle weakness and dilated cardiomyopathy. She exhibited predominantly distal weakness with early toe walking. Dilated cardiomyopathy required cardiac transplantation at age 15 years. We identified a de-novo, heterozygous, missense mutation, c.2348G>C (p. Arg783Pro), in exon 21 of the MYH7 gene, which encodes slow skeletal muscle fiber/ß-cardiac myosin heavy chain protein, that replaces a highly conserved arginine with a proline. This novel mutation that results in the unusual combined cardiac and skeletal muscle phenotype localizes to the essential light chain binding area, a region only previously shown to be mutated in hypertrophic cardiomyopathy.