Am J Med Genet A. 2015 Mar;167A(3):629-34. doi: 10.1002/ajmg.a.36924.

Sequencing of channelopathy genes with the BpG Arrhythmia Panel revealed a de novo mutation in the CACNA1C gene in an adolescent with ventricular fibrillation but normal development, consequently not only expanding the phenotype of Timothy Syndrome Type 2 but also demonstrating the power of large gene panels. The standard has been to select specific gene tests for patients with established clinical diagnoses, however the sometimes even surprising overlap between genotypes and phenotypes supports the use of comprehensive gene panels. This first published case report illustrates beautifully how our unique targeted sequencing method (OS-Seq) was applied successfully in establishing the genetic diagnosis in a patient where simply clinical examination and traditional genotype-phenotype approach would have failed to determine the underlying disease mechanism.

Abstract

Timothy syndrome is a rare multiorgan disorder with prolonged QTc interval, congenital heart defects, syndactyly, typical facial features and neurodevelopmental problems. Ventricular tachyarrhythmia is the leading cause of death at early age. Classical Timothy syndrome type 1 (TS1) results from a recurrent de novo CACNA1C mutation, G406R in exon 8 A. An atypical form of Timothy syndrome type 2 (TS2) is caused by mutations in G406R and G402S in the alternatively spliced exon 8. Only one individual for each exon 8 mutations has been described. In contrast to multiorgan disease caused by the mutation in G406R either in exon 8 A or 8, the G402S carrier manifested only an isolated cardiac phenotype with LQTS and cardiac arrest. We describe a teenage patient resuscitated from ventricular fibrillation and treated with an implantable cardioverter defibrillator. She has no other organ manifestations, no syndactyly, normal neurodevelopment and her QTc has ranged between 440-480 ms. There is no family history of arrhythmias or sudden death. Targeted oligonucleotide-selective sequencing(OS-Seq) of channelopathy genes revealed a de novo substitution, G402S in exon 8 of CACNA1C. Direct sequencing of blood and saliva derived DNA showed an identical mutation peak suggesting ubiquitous expression in different tissues. The phenotype of our patient and the previously described patient show an isolated arrhythmia disease with no other organ manifestations of classical Timothy syndrome.

Hiippala A, Tallila J, Myllykangas S, Koskenvuo JW, Alastalo TP