Sedaghatian-type spondylometaphyseal dysplasia (SMDS) is a rare lethal disorder characterized by severe metaphyseal chondrodysplasia with mild limb shortening, platyspondyly, delayed epiphyseal ossification, irregular iliac crests, and pulmonary hemorrhage. Affected infants present with severe hypotonia and cardiorespiratory problems; most die within days of birth due to respiratory failure. Cardiac abnormalities include conduction defects, complete heart block, and structural anomalies. Half of infants with SMDS are reported to have central nervous system malformations consistent with abnormal neuronal migration, including agenesis of the corpus callosum, pronounced frontotemporal pachygyria, simplified gyral pattern, partial lissencephaly, and severe cerebellar hypoplasia (summary by Smith et al., 2014).

LQT14 is a cardiac arrhythmia disorder characterized by ventricular arrhythmias, often life-threatening, occurring very early in life, frequent episodes of T-wave alternans, markedly prolonged QTc intervals, and intermittent 2:1 atrioventricular block (Crotti et al., 2013). Patients with LQT14, LQT15 (616249), or LQT16 (618782), resulting from mutation in calmodulin genes CALM1, CALM2 (114182), or CALM3 (114183), 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).