LAUSR

Key Teaching Points • Electrocardiograms in patients with Timothy syndrome patients sometimes present T-wave depolarization pattern similar to long QT syndrome type 3, such as a late-onset peaked T wave. • We identified a novel CACNA1C mutation, S643F, in a 14-year-old boy with Timothy syndrome without syndactyly. • S643F is located within the Cav1.2 S4–S5 linker of domain II, and the mutant channel exerts both marked loss-of function and gain-of-function effects.