Familial KCNQ2 mutation: a psychiatric perspective

KCNQ2 mutations are a common cause of early-onset epileptic syndromes. They are associated with heterogeneous developmental profiles, from mild to severe cognitive and social impairments that need better characterization. We report a case of an inherited KCNQ2 mutation due to a deletion c.402delC in a heterozygous state, in the exon 3 of the KCNQ2 gene. A 5-year-old boy presented a cluster of sudden-onset generalized tonic-clonic seizures at three months of age, after an unremarkable postnatal period. Multiplex ligation-dependent probe amplification identified a familial mutation after an investigation in the family revealed that this mutation was present on the father's side. The patient was diagnosed with autism and intellectual deficiency in a context of KCNQ2 -encephalopathy. We describe his clinical features in light of current literature. This report highlights the importance of appropriate genetic counseling and psychiatric assessment in planning the medical and social follow-up of a disorder with complex socio-behavioral features.

A Case of Early Infantile Epileptic Encephalopathy Due to KCNQ2 Gene Mutation Presenting With Episodes of Hiccups

Neonatal epilepsy syndromes are responsible for only 15% of the cases of neonatal seizure. An underlying genetic disorder can be detected in approximately 42% of this subgroup. KCNQ2 gene-associated epilepsies are very rare and more common presentations are self-limited familial neonatal epilepsy (SLFNE) and early infantile epileptic encephalopathies (EIEE). The most common initial seizure semiologies are tonic seizures with or without autonomic symptoms in EIEE resulting from KCNQ2 gene mutation. It is characterized by early neonatal onset seizures with suppression burst pattern on electroencephalogram and typically results in severe developmental delay. Therapeutic options for infants with KCNQ2-related EIEE are limited and there is no consensus about it in the literature. Herein, the neonate with EIEE with unexpected episodes of hiccups due to novel mutation of the KCNQ2 gene, which was reported second time, was presented and antiepileptic treatment strategies were discussed in the light of current literature.

Deciphering Developmental Disorders Study. Prevalence and architecture of de novo mutations in developmental disorders

The genomes of individuals with severe, undiagnosed developmental disorders are enriched in damaging de novo mutations (DNMs) in developmentally important genes. Here we have sequenced the exomes of 4,293 families containing individuals with developmental disorders, and meta-analysed these data with data from another 3,287 individuals with similar disorders. We show that the most important factors influencing the diagnostic yield of DNMs are the sex of the affected individual, the relatedness of their parents, whether close relatives are affected and the parental ages. We identified 94 genes enriched in damaging DNMs, including 14 that previously lacked compelling evidence of involvement in developmental disorders. We have also characterized the phenotypic diversity among these disorders. We estimate that 42% of our cohort carry pathogenic DNMs in coding sequences; approximately half of these DNMs disrupt gene function and the remainder result in altered protein function. We estimate that developmental disorders caused by DNMs have an average prevalence of 1 in 213 to 1 in 448 births, depending on parental age. Given current global demographics, this equates to almost 400,000 children born per year.

Differential expression of kcnq2 splice variants: implications to m current function during neuronal development

The KCNQ family of K(+) channels has been implicated in several cardiac and neurological disease pathologies. KCNQ2 (Q2) is a brain-derived gene, which in association with KCNQ3 (Q3) has been shown to provide a molecular basis for the neuronal M current. We have cloned a long (Q2L) and a short (Q2S) splice variant of the human KCNQ2 gene; these variants differ in their C-terminal tail. Northern blot analysis reveals that Q2L is preferentially expressed in differentiated neurons, whereas the Q2S transcript is prominent in fetal brain, undifferentiated neuroblastoma cells, and brain tumors. Q2L, transfected into mammalian cells, produces a slowly activating, noninactivating voltage-gated K(+) current that is blocked potently by tetraethylammonium (TEA; IC(50), 0.14 mm). Q2S on the other hand produces no measurable potassium currents. Cotransfection of Q2S with either Q2L, Q3, or Q2L/Q3 heteromultimers results in attenuation of K(+) current, the suppression being most profound for Q3. Inclusion of Q2S in the heteromultimer also positively shifts the voltage dependence of current activation and alters affinity for the TEA block, suggesting that under these conditions, some Q2S subunits incorporate into functional channels on the plasma membrane. In view of the crucial role of M currents in modulating neuronal excitability, our findings provide important insight into the functional consequences of differential expression of KCNQ2 splice variants: dampened potassium conductances in the developing brain could shape firing repertoires to provide cues for proliferation rather than differentiation.