Refer to the passage below and then answer the question afterwards in the same language as the passage:

Passage: There are two recognized types of Timothy syndrome, classical (type-1) and atypical (type-2). They are both caused by mutations in CACNA1C, the gene encoding the calcium channel Cav1.2 α subunit. Timothy syndrome mutations in CACNA1C cause delayed channel closing, thus increased cellular excitability.

Question: What gene is being mutated?
CACNA1C