Genotype-Phenotype Associations in Pediatric Hypertrophic Cardiomyopathy: A Study From the Pediatric Cardiomyopathy Registry.

BACKGROUND: Genotype-phenotype correlations in pediatric hypertrophic cardiomyopathy (HCM) are not well established. Determining whether specific genes or variants correlate with disease severity may impact clinical care. OBJECTIVES: This study aims to identify associations between pathogenic genetic variants in pediatric HCM and echocardiographic maximal left ventricular wall thickness. METHODS: Children with primary HCM from pediatric cardiomyopathy centers were recruited for research-based exome sequencing. Associations between genetic findings, imaging, and clinical outcomes were assessed. Genetic variants in established HCM genes were classified according to established guidelines. Left ventricular hypertrophy (LVH) at enrollment was classified as mild (z-score <12), moderate (z-score ≥12), or severe (z-score ≥17) based on LV septal or posterior wall thickness z-scores measured by a core echocardiography laboratory. RESULTS: Severity of LVH was determined in 143 children with adequate echocardiograms. The median age at enrollment was 11.5 years (range: 3.8-14.4 years). Overall, 51% had a pathogenic variant, of which 93% were in sarcomeric genes. Children with severe LVH (n = 40, 28%) were diagnosed at younger ages than those with mild LVH (n = 78, 55%) at a median of 6.4 vs 12.9 years, P = 0.005. Those with severe LVH were more likely to have pathogenic variants; this association was driven by variants in MYBPC3 (OR: 4.1; 95% CI: 1.7-9.9). Missense variants in MYBPC3 predominated over stop, insertion-deletion, or splicing variants in severe cases. CONCLUSIONS: In this population of children with primary HCM, severe LVH was associated with a younger age at enrollment and a higher likelihood of harboring a pathogenic variant in MYBPC3. (Genotype-Phenotype Associations in Pediatric Cardiomyopathy [PCM GENES]; NCT01873963).