A Neurodevelopmental Disorder Caused by a Dysfunctional Allele

P/Q-type Ca flux into nerve terminals Ca2.1 channels is essential for neurotransmitter release at neuromuscular junctions and nearly all central synapses. Mutations in , the gene encoding Ca2.1, cause a spectrum of pediatric neurological disorders. We have identified a patient harboring an autosomal-dominant frameshift-causing nucleotide duplication in (c.5018dupG). The duplicated guanine precipitated 43 residues of altered amino acid sequence beginning with a glutamine to serine substitution in Ca2.1 at position 1674 ending with a premature stop codon (Ca2.1 p.Gln1674Serfs*43). The patient presented with episodic downbeat vertical nystagmus, hypotonia, ataxia, developmental delay and febrile seizures. In patch-clamp experiments, no Ba current was observed in tsA-201 cells expressing Ca2.1 p.Gln1674Serfs*43 with β and αδ-1 auxiliary subunits. The ablation of divalent flux in response to depolarization was likely attributable to the inability of Ca2.1 p.Gln1674Serfs*43 to form a complete channel pore. Our results suggest that the pathology resulting from this frameshift-inducing nucleotide duplication is a consequence of an effective haploinsufficiency.