A nonsense variant in HERC1 is associated with intellectual disability,megalencephaly, thick corpus callosum and cerebellar atrophy

Megalencephaly is a congenital condition characterized by severe overdeveloped brain size. This phenotype is often caused by mutations affecting the RTK/PI3K/mTOR (receptor tyrosine kinase-phosphatidylinositol-3-kinase-AKT) signaling and its downstream pathway of mammalian target of rapamycin (mTOR). Here, using a whole-exome sequencing in a Moroccan consanguineous family, we show that a novel autosomal-recessive neurological condition characterized by megalencephaly, thick corpus callosum and severe intellectual disability is caused by a homozygous nonsense variant in the HERC1 gene. Assessment of the primary skin fibroblast from the proband revealed complete absence of the HERC1 protein. HERC1 is an ubiquitin ligase that interacts with tuberous sclerosis complex 2, an upstream negative regulator of the mTOR pathway. Our data further emphasize the role of the mTOR pathway in the regulation of brain development and the power of next-generation sequencing technique in elucidating the genetic etiology of autosomal-recessive disorders and suggest that HERC1 defect might be a novel cause of autosomal-recessive syndromic megalencephaly.     

Novel BRPF1 mutation in a boy with intellectual disability,coloboma, facial nerve palsy and hypoplasia of the corpus callosum

Mutations in the chromatin regulator gene BRPF1 were recently associated with the Intellectual Developmental Disorder With Dysmorphic Facies And Ptosis (IDDDFP). Up till now, clinical data of 22 patients are reported. Besides intellectual disability (ID), ptosis and blepharophimosis are frequent findings, with refraction problems, amblyopia and strabism as other reported ophthalmological features. Animal studies indicate BRPF1 as an important mediator in brain development. However, only 5 of 22 previously reported patients show structural brain abnormalities.We report on an additional patient harboring a novel de novo nonsense mutation p.(Glu219*) in BRPF1. He presented with ID, bilateral iris colobomas, facial nerve palsy and severe hypoplasia of the corpus callosum. Our findings support previous findings of brain abnormalities in BRPF1-mutations and indicates coloboma and facial nerve palsy as possible additional features of IDDDFP syndrome.     

Variants in NGLY1 lead to intellectual disability,myoclonus epilepsy,sensorimotor axonal polyneuropathy and mitochondrial dysfunction

NGLY1 encodes the enzyme N-glycanase that is involved in the degradation of glycoproteins as part of the endoplasmatic reticulum-associated degradation pathway. Variants in this gene have been described to cause a multisystem disease characterized by neuromotor impairment, neuropathy, intellectual disability, and dysmorphic features. Here, we describe four patients with pathogenic variants in NGLY1. As the clinical features and laboratory results of the patients suggested a multisystem mitochondrial disease, a muscle biopsy had been performed. Biochemical analysis in muscle showed a strongly reduced ATP production rate in all patients, while individual OXPHOS enzyme activities varied from normal to reduced. No causative variants in any mitochondrial disease genes were found using mtDNA analysis and whole exome sequencing. In all four patients, variants in NGLY1 were identified, including two unreported variants (c.849T>G (p.(Cys283Trp)) and c.1067A>G (p.(Glu356Gly)). Western blot analysis of N-glycanase in muscle and fibroblasts showed a complete absence of N-glycanase. One patient showed a decreased basal and maximal oxygen consumption rates in fibroblasts. Mitochondrial morphofunction fibroblast analysis showed patient specific differences when compared to control cell lines. In conclusion, variants in NGLY1 affect mitochondrial energy metabolism which in turn might contribute to the clinical disease course.     

Corpus callosum abnormalities, intellectual disability, speech impairment, and autism in patients with haploinsufficiency of ARID1B

Corpus callosum abnormalities, intellectual disability, speech impairment, and autism in patients with haploinsufficiency of ARID1B. Corpus callosum abnormalities are common brain malformations with a wide clinical spectrum ranging from severe intellectual disability to normal cognitive function. The etiology is expected to be genetic in as much as 30-50% of the cases, but the underlying genetic cause remains unknown in the majority of cases. By next-generation mate-pair sequencing we mapped the chromosomal breakpoints of a patient with a de novo balanced translocation, t(1;6)(p31;q25), agenesis of corpus callosum (CC), intellectual disability, severe speech impairment, and autism. The chromosome 6 breakpoint truncated ARID1B which was also truncated in a recently published translocation patient with a similar phenotype. Quantitative polymerase chain reaction (Q-PCR) data showed that a primer set proximal to the translocation showed increased expression of ARID1B, whereas primer sets spanning or distal to the translocation showed decreased expression in the patient relative to a non-related control set. Phenotype-genotype comparison of the translocation patient to seven unpublished patients with various sized deletions encompassing ARID1B confirms that haploinsufficiency of ARID1B is associated with CC abnormalities, intellectual disability, severe speech impairment, and autism. Our findings emphasize that ARID1B is important in human brain development and function in general, and in the development of CC and in speech development in particular.     

Mutations in the PFN1 gene are not a common cause in patients with amyotrophic lateral sclerosis and frontotemporal lobar degeneration in France

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are 2 adult onset neurological disorders with overlapping symptoms and clinical characteristics. It is well established that they share a common pathologic and genetic background. Recently, mutations in profilin 1 gene (PFN1) have been identified in patients with familial ALS, suggesting a role for this gene in the pathogenesis of the disease. Based on this, we hypothesized that mutations in PFN1 might also contribute to FTLD disease. We studied a French cohort of 165 ALS/FTLD patients, without finding any variant. We conclude that mutations in PFN1 are not a common cause for ALS/FTLD in France.     

Hallux duplication,postaxial polydactyly,absence of the corpus callosum,severe mental retardation,and additional anomalies in two unrelated patients: A new syndrome

Two unrelated patients, a 4-year-old boy and a 2 1/2-year-old girl, presented with a similar pattern of abnormalities. Both had severe mental retardation, macrocephaly, absence of the corpus callosum, unusual facial appearance, duplication of hallucal phalanges, postaxial hexadactyly of finger phalanges, and 2/3-syndactyly of toes. The boy also had postaxial hexadactyly of toe phalanges, inguinal hernias and umbilical hernia, and growth retardation. We suspect a common cause of this apparently “new” syndrome, most likely a gene mutation.