Timothy syndrome type 1 (TS-1) is a rare disorder that affects multiple organ 
systems and has a high incidence of sudden death due to profound QT prolongation 
and resultant ventricular arrhythmias. 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). Most 
patients reported in the literature represent highly affected individuals who 
present early in life with severe cardiac and neurological manifestations. Here, 
we describe somatic mosaicism in TS-1 patients with less severe manifestations 
than the typical TS-1 patient. These findings suggest that the TS prognosis may 
not be as dismal as previously reported. Moreover, our findings have 
implications for genetic counseling in that previously described de novo TS 
mutations may represent cases of parental mosaicism and warrant careful 
genotyping of parental tissue other than peripheral blood lymphocytes.