Rapidly Progressive Infantile Dilated Cardiomyopathy in Long-Olsen-Distelmaier Syndrome Associated with RRAGC NM_022157.4:c.343T>C, p.(Trp115Arg): A Case Report.

Background: Infantile dilated cardiomyopathy (DCM) is uncommon but carries substantial mortality, particularly when accompanied by neurological, ocular, or metabolic abnormalities. Long-Olsen-Distelmaier syndrome is a rare mTORopathy caused by heterozygous gain-of-function variants in RRAGC and may include cortical malformations, congenital cataracts, mineral disturbances, and early-onset DCM. Case Summary: We describe a term male infant born to consanguineous parents with hypocalcemia and hyperphosphatemia, bilateral frontoparietal polymicrogyria, bilateral congenital lamellar cataracts, small patent ductus arteriosus and ventricular septal defect, and initially preserved biventricular function. At 53 days of age, he developed cardiogenic shock, severe lactic acidosis, and hyperkalemia during a rhinovirus/enterovirus-positive respiratory illness. Echocardiography showed severe DCM with marked left ventricular dilatation and an ejection fraction of 27%. Despite multi-agent inotropic support, ventricular function did not recover, and he died at approximately two months. Accordingly, the contemporaneous clinical WES record documented a heterozygous RRAGC c.343T>C, p.(Trp115Arg) variant, reported by the diagnostic laboratory as likely pathogenic. The variant was subsequently standardized in this manuscript as NM_022157.4:c.343T>C, and an independent manuscript-level ACMG/AMP reassessment was concordant. Conclusions: Because p.(Trp115Arg) was previously reported, the principal contribution is detailed documentation of rapid progression from preserved neonatal ventricular function to fatal infantile DCM, while extending the clinical and geographic spectrum of RRAGC-related Long-Olsen-Distelmaier syndrome. Respiratory viral detection should be interpreted cautiously because myocarditis was not established; early exome-based testing should be considered in infants with cardiomyopathy and multisystem abnormalities.