Severe Dilated Cardiomyopathy with PLACK Syndrome Caused by a Novel Truncating Variant in the CAST Gene

Background: PLACK syndrome is an ultra-rare autosomal recessive disorder caused by biallelic loss-of-function variants in CAST, which encodes calpastatin, an endogenous inhibitor of calpains. The syndrome is classically defined by peeling skin, leukonychia, acral punctate keratoses, cheilitis, and knuckle pads. Although the phenotype has been largely restricted to dermatological manifestations, emerging reports suggest dilated cardiomyopathy (DCM) as a systemic complication. Methods: We investigated five affected children from three sibships of an extended consanguineous family. Clinical evaluation and genome sequencing (GS) followed by segregation analysis of the targeted mutation test (TMT) were performed. Histopathological examination of an explanted heart was conducted in one child who underwent heart transplantation. Results: All affected children exhibited typical dermatological features of PLACK syndrome. Four developed severe DCM, two of whom required orthotopic heart transplantation. GS, performed in three affected children, identified a novel homozygous frameshift variant in CAST (NM_001750.7:c.1177dup, p.Arg393Profs*4), which segregated with the disease within the family. No additional plausible variants in known cardiomyopathy-associated genes were detected. Histopathological examination of the explanted heart demonstrated hypertrophied cardiomyocytes with nuclear enlargement, hyperchromasia, and fibrosis. Conclusions: Our findings expand the phenotypic spectrum of PLACK syndrome to include severe DCM and suggest CAST deficiency as a novel cause of recessively inherited cardiomyopathy. The favorable short-term outcome following transplantation highlights a potential therapeutic option. Given the possibility of age-dependent penetrance, lifelong cardiac surveillance is for the affected individuals suggested. To emphasize cardiomyopathy as a critical and underrecognized component of the syndrome, we propose the consideration of modifying the acronym to PLACK-C.