Although full TS1 is caused by a single missense mutation in the CACNA1C-encoded cardiac calcium channel, mosaic TS1 parents can display isolated syndactyly without additional phenotypic manifestations.
To our knowledge, this patient is the first to exhibit syndactyly and to carry a CACNA1C mutation but to not have QT prolongation, which has long been considered an obligatory feature of Timothy syndrome.
The gene families and genetic lesions underlying familial hemiplegic migraine, FHM1/CACNA1A, FHM2/ATP1A2, and FHM3/SCN1A, and monogenic mitochondrial migraine syndromes, provide a robust platform from which genes, such as CACNA1C, which encodes the calcium channel mutated in Timothy syndrome, can be evaluated for their role in autism and bipolar disease.
The Shank3 models mimick gene mutations associated with Phelan-McDermid Syndrome and the Cacna1c model recapitulates the deletion underlying Timothy syndrome.
The Timothy syndrome mutation is a rare de novo gain-of-function variant in CACNA1C that causes autism with high penetrance, providing a powerful avenue into investigating the role of CACNA1C variants in neurodevelopmental disorders.
The identification of a gain-of-function mutation in CACNA1C as the cause of Timothy Syndrome (TS), a rare disorder characterized by cardiac arrhythmias and syndactyly, highlighted unexpected roles for the L-type voltage-gated Ca2+ channel CaV1.2 in nonexcitable cells.
By altering the kinetic parameters, the mutations are reminiscent of the CACNA1C mutation causing Timothy Syndrome, a Mendelian disease presenting with ASD.
This study aimed to elucidate the frequency of CACNA1C mutations in patients with long QT syndrome (LQTS), except those with Timothy syndrome and investigate phenotypic variants.
All previously described cases of TS-1 are the result of a missense mutation in exon 8A (p.G406R), an alternatively spliced variant of the L-type calcium channel gene (Ca(v)1.2, CACNA1C).
Timothy Syndrome (TS) is caused by very rare exonic mutations of the CACNA1C gene that produce delayed inactivation of Cav1.2 voltage-gated calcium channels during cellular action potentials, with greatly increased influx of calcium into the activated cells.
Initial targeted mutation analysis did not identify either of the previously describedTS associated mutations; however, full gene sequencing detected a novel CACNA1C gene mutation (p.Ala1473Gly).
Timothy syndrome (TS) is a congenital long QT syndrome that is associated with syndactyly and mutations in CACNA1C, encoding an L-type voltage-dependent calcium channel, Cav1.2.
Comprehensive review and topological mapping of all described CACNA1C mutations revealed TS-specific hotspots localizing to the cytoplasmic aspect of 6th transmembrane segment of respective domains.
We conclude that genotype-negative LQTS patients should be investigated for mutations in CACNA1C, as a gain-of-function in Cav1.2 is likely to cause LQTS and only specific and rare mutations, i.e. in exon 8, cause the multi-systemic TS.
Mutations in CACNA1C that increase current through the CaV1.2 L-type Ca2+ channel underlie rare forms of long QT syndrome (LQTS), and Timothy syndrome (TS).
The identification of a functional CACNA1C mutation cosegregating with disease in a single pedigree suggests that CACNA1C perturbations may underlie autosomal dominant LQTS in the absence of Timothy syndrome.
TRPM4 enlarges the subgroup of LQT genes (KCNJ2 in Andersen syndrome and CACNA1C in Timothy syndrome) known to increase the QT interval through a more complex pleiotropic effect than merely action potential alteration.