Autosomal recessive cutis laxa type IIC (ARCL2C) is characterized by generalized skin wrinkling with sparse subcutaneous fat and dysmorphic progeroid facial features. Most patients also exhibit severe hypotonia as well as cardiovascular involvement (summary by Van Damme et al., 2017). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal recessive cutis laxa, see ARCL1A (219100).

LQT16 Long QT syndrome-16 (LQT16) is characterized by a markedly prolonged corrected QT (QTc) interval and 2:1 atrioventricular (AV) block, with onset in the perinatal period. Patients experience bradycardia or ventricular tachyarrhythmias that may result in syncope, cardiac arrest, and/or sudden death (Reed et al., 2015; Wren et al., 2019). Patients with LQT14 (616247), LQT15 (616249), or LQT16, resulting from mutation in calmodulin genes CALM1 (114180), CALM2 (114182), or CALM3, respectively, typically have a more severe phenotype, with earlier onset, profound QT prolongation, and a high predilection for cardiac arrest and sudden death, than patients with mutations in other genes (Boczek et al., 2016). CPVT6 Catecholaminergic polymorphic ventricular tachycardia-6 (CPVT6) is characterized by childhood-onset syncopal episodes with exercise or stress. Electrocardiogram (ECG) shows a normal QT interval with a prominent U wave, and stress testing reveals premature ventricular contractions (PVCs) that may occur as bigeminy or couplets, and nonsustained ventricular tachycardia (Gomez-Hurtado et al., 2016).