High Prevalence of Structural Heart Disease in Children with CblC-type Methylmalonic Aciduria and Homocystinuria

Objective: To characterize the frequency and nature of cardiovascular defects in patients with CblC-type methylmalonic aciduria and homocystinuria (cblC), an inborn error of cobalamin (vitamin B12) metabolism resulting in accumulation of methylmalonic acid and homocysteine.

Study Design: A retrospective observational study was conducted investigating 10 patients with cblC ranging in age from 2 weeks to 24 years (mean 4.4 years +/- 7.5 years, median 0.6 years). All patients underwent a complete 2-D echocardiogram including quantitative assessment of left ventricular systolic function.

Results: Structural heart defects were detected in 50% of patients with cblC. Heart defects included left ventricular (LV) non-compaction (3), secundum atrial septal defect (2), muscular ventricular septal defect (1), dysplastic pulmonary valve without pulmonary stenosis (1) and mitral valve prolapse with mild mitral regurgitation (1). One patient had resolved cor pulmonale and right heart failure secondary to pulmonary embolism. All patients had quantitatively normal LV systolic function.

Conclusions: Diverse and clinically significant structural heart defects appear to be highly prevalent in cblC, perhaps due to abnormal DNA and histone methylation during embryogenesis. The specific cardiac defects detected in our cohort were variable, and studies with a larger number of patients are needed to establish which forms are most common. Routine and periodic cardiovascular evaluation may be indicated in patients with cblC.