SLC22A2 and systemic primary carnitine deficiency disease: Carnitine levels were measured as part of her diagnostic workup, discovering a rare, reversible cause of short QT syndrome (SQTS) and associated cardiomyopathy-primary carnitine deficiency (PCD) caused by a homozygous mutation in the SLC22A5 gene, leading to an in-frame deletion mutation (NP_003051.1:p.Phe23del) affecting the organic cation transporter 2 (OCTN2) protein.