Atypical vitamin B6 deficiency: a rare cause of unexplained neonatal and infantile epilepsies

ALDH7A1 and PNPO deficiencies are rare inborn errors of vitamin B6 metabolism causing perinatal seizure disorders. The phenotypic variability, however, is broad. To assess the frequency of these deficiencies in unexplained infantile epilepsy, we screened 113 patients for mutations in both genes. We identified 1 patient with an epilepsy phenotype resembling Dravet syndrome and likely pathogenic mutations in ALDH7A1. Presenting features were highly atypical of pyridoxine-dependent epilepsy, including febrile seizures, response to anticonvulsive drugs, and periods of seizure freedom without pyridoxine treatment. "Hidden" vitamin B6 deficiencies might be rare but treatable causes of unexplained epilepsy extending beyond the classical phenotypes.

Reduced ceramide synthase 2 activity causes progressive myoclonic epilepsy

Objective

Ceramides are precursors of complex sphingolipids (SLs), which are important for normal functioning of both the developing and mature brain. Altered SL levels have been associated with many neurodegenerative disorders, including epilepsy, although few direct links have been identified between genes involved in SL metabolism and epilepsy.

Methods

We used quantitative real-time PCR, Western blotting, and enzymatic assays to determine the mRNA, protein, and activity levels of ceramide synthase 2 (CERS2) in fiibroblasts isolated from parental control subjects and from a patient diagnosed with progressive myoclonic epilepsy (PME). Mass spectrometry and fluorescence microscopy were used to examine the effects of reduced CERS2 activity on cellular lipid composition and plasma membrane functions.

Results

We identify a novel 27 kb heterozygous deletion including the CERS2 gene in a proband diagnosed with PME. Compared to parental controls, levels of CERS2 mRNA, protein, and activity were reduced by ˜50% in fibroblasts isolated from this proband, resulting in significantly reduced levels of ceramides and sphingomyelins containing the very long-chain fatty acids C24:0 and C26:0. The change in SL composition was also reflected in a reduction in cholera toxin B immunofluorescence, indicating that membrane composition and function are altered.

Interpretation

We propose that reduced levels of CERS2, and consequently diminished levels of ceramides and SLs containing very long-chain fatty acids, lead to development of PME.

Exon-disrupting deletions of NRXN1 in idiopathic generalized epilepsy

PURPOSE

Neurexins are neuronal adhesion molecules located in the presynaptic terminal, where they interact with postsynaptic neuroligins to form a transsynaptic complex required for efficient neurotransmission in the brain. Recently, deletions and point mutations of the neurexin 1 (NRXN1) gene have been associated with a broad spectrum of neuropsychiatric disorders. This study aimed to investigate if NRXN1 deletions also increase the risk of idiopathic generalized epilepsies (IGEs).

METHODS

We screened for deletions involving the NRXN1 gene in 1,569 patients with IGE and 6,201 controls using high-density oligonucleotide microarrays.

KEY FINDINGS

We identified exon-disrupting deletions of NRXN1 in 5 of 1,569 patients with IGE and 2 of 6,201 control individuals (p = 0.0049; odds ratio (OR) 9.91, 95% confidence interval (CI) 1.92-51.12). A complex familial segregation pattern in the IGE families was observed, suggesting that heterozygous NRXN1 deletions are susceptibility variants. Intriguingly, we identified a second large copy number variant in three of five index patients, supporting an involvement of heterogeneous susceptibility alleles in the etiology of IGE.

SIGNIFICANCE

We conclude that exon-disrupting deletions of NRXN1 represent a genetic risk factor in the genetically complex predisposition of common IGE syndromes.

Mutations in SYNGAP1 cause intellectual disability, autism, and a specific form of epilepsy by inducing haploinsufficiency

De novo mutations in SYNGAP1, which codes for a RAS/RAP GTP-activating protein, cause nonsyndromic intellectual disability (NSID). All disease-causing point mutations identified until now in SYNGAP1 are truncating, raising the possibility of an association between this type of mutations and NSID. Here, we report the identification of the first pathogenic missense mutations (c.1084T>C [p.W362R], c.1685C>T [p.P562L]) and three novel truncating mutations (c.283dupC [p.H95PfsX5], c.2212_2213del [p.S738X], and (c.2184del [p.N729TfsX31]) in SYNGAP1 in patients with NSID. A subset of these patients also showed ataxia, autism, and a specific form of generalized epilepsy that can be refractory to treatment. All of these mutations occurred de novo, except c.283dupC, which was inherited from a father who is a mosaic. Biolistic transfection of wild-type SYNGAP1 in pyramidal cells from cortical organotypic cultures significantly reduced activity-dependent phosphorylated extracellular signal-regulated kinase (pERK) levels. In contrast, constructs expressing p.W362R, p.P562L, or the previously described p.R579X had no significant effect on pERK levels. These experiments suggest that the de novo missense mutations, p.R579X, and possibly all the other truncating mutations in SYNGAP1 result in a loss of its function. Moreover, our study confirms the involvement of SYNGAP1 in autism while providing novel insight into the epileptic manifestations associated with its disruption.

Genetic studies in congenital anterior midline cervical cleft

Congenital anterior midline cervical cleft (CAMCC) is a rare anomaly, with less than 100 cases reported. The cause of CAMCC is unknown, but genetic factors must be considered as part of the etiology. Three cases of CAMCC are presented. This is the first genetic study of isolated CAMCC. Conventional cytogenetics, array-comparative genomic hybridization (CGH) and whole exome sequencing were performed, including a search of relevant syndromes in the Online Mendelian Inheritance in Man (OMIM) database. Array CGH indicated a loss of the PAPPA gene in one of the patients, while exome sequencing showed a mutation in SIX5 in another patient. Both aberrations were inherited from unaffected parents. These results most likely imply that the identified mutations are not disease-causing, although they may be contributing factors if CAMCC has a polygenic inheritance.

Mutations in NRXN1 in a family multiply affected with brain disorders: NRXN1 mutations and brain disorders

Mutation of the neurexin1-gene, NRXN1, interrupting the expression of neurexin1 has been associated with schizophrenia, autism, and intellectual disability. We have identified a family multiply affected with psychiatric, neurological, and somatic disorders along with an intricate co-segregation of NRXN1 mutations. The proband suffered from autism, mental retardation, and epilepsy and on genotyping it was revealed that he carried a compound heterozygous mutation in the NRXN1 consisting of a 451 kb deletion, affecting the promoter and first introns in addition to a point mutation, predicted to be deleterious to NRXN1. The deletion was passed on from the patient's mother who was clinically characterized by sub-diagnostic autistic traits in addition to type 1 diabetes mellitus. The point mutation was subsequently found in the patient's brother, suffering from a psychotic disorder, which implies that the point mutation was inherited from the deceased father, who was diagnosed with schizophrenia. The observations suggest a possible gene-dose effect of NRXN1 mutations on type and severity of mental illness and support the notion that the penetrance and pleiotropy of pathogenic CNVs in general are determined by additional genetic variants in the genome. Finally the findings also propose a linkage of NRXN1 neurobiology to epilepsy and possibly to type 1 diabetes.

A balanced translocation disrupts SYNGAP1 in a patient with intellectual disability, speech impairment, and epilepsy with myoclonic absences (EMA)

Epilepsy with myoclonic absences (EMA) is a rare form of generalized epilepsy occurring in childhood and is often difficult to treat. The underlying etiology of EMA is unknown in the majority of patients. Herein, we describe a patient with EMA and intellectual disability who carries a de novo balanced translocation: t(6;22)(p21.32;q11.21). We mapped the translocation breakpoints by fluorescence in situ hybridization (FISH), and the breakpoint at 6p21.32 was found to truncate the N-methyl-d-aspartate (NMDA)-receptor associated gene SYNGAP1. The breakpoint at 22q11.21 was within a highly variable region without known protein-coding genes. Mutations of SYNGAP1 are associated with nonsyndromal intellectual disability (NSID). Two-thirds of the patients described so far also have generalized epilepsy. This finding, together with our report, suggests that dysfunction of SYNGAP1 contributes to the development of generalized epilepsy, including EMA.