Mutation screening in sarcomeric genes in Italian HCM paediatric population

Introduction and Aim: The hypertrophic cardiomyopathy (HCM) is a primary disease of the heart muscle, transmitted by an autosomal dominant character, with a highly variable penetrance and expressivity, even within the same family cluster. Hundreds of mutations in at least 15 different genes have been implicated in the pathogenesis of HCM, most of which encode sarcomeric proteins. In adults systematic screening for sarcomeric defects accounts for about 60% of cases. To date, little is known about the prevalence, genotype and clinical features of early-onset HCM. Our study is looking for mutations, in a Sud-Italian paediatric HCM patients, in the genes most frequently mutated in adult HCM: beta-myosin heavy chain (MYH7), myosin binding protein C (MYBPC3), cardiac troponins T and I (TNNT2 and TNNI3) and alpha-tropomyosin (TPM1) genes, Materials and methods. The diagnosis of HCM was placed in 39 independent patients (age at diagnosis < 18 years), in which, after careful personal and family medical history, evaluation of clinical symptoms and signs, and instrumental assessment (echo-Doppler, ECG, and Holter in 24 hours), secondary causes of left ventricular hypertrophy were excluded. Family medical history revealed 18 familial cases. The mutations research was performed by PCR, dHPLC (denaturing high performance liquid chromatography) and sequencing of the MYH7, MYBPC3, TNNT2, TNNI3 and TPM1 genes. Results. We identified 9 different mutations in 13 of 39 independent HCM patients: 5 in MYH7 gene, 2 in MYBPC3 gene and 2 in TNNT2 gene: 1 patient carried two mutations; 2 missense mutations were found in more than one proband (p.R719W [n=3], and p.M539L [n=4] in MYH7 gene). None mutation was discovered in TNNI3 and TPM1 genes. The p.R719W and p.G716R mutations, already known as MYH7 "malignant" mutations, was found in 4 patients, all characterized by a phenotype considered at risk for sudden death, and that has required the installation of a defibrillator in 2 patients (one in primary prevention). The other seven mutations (p.M539L, p.R1045H and p.D1652Y in MYH7 gene; p.V906G and R495G in MYBPC3 gene; p.V95M and p.R104H in TNNT2 gene) are never previously described in the literature, are located in highly conserved gene regions and has not been found in an at least 120 healthy subjects control population. Particularly, the p.M539L in MYH7 gene was found in 4 independent patients, with variables HCM phenotypes; the R495G in MYBPC3 gene was identified, for the first time, in a family with non-compaction cardiomyopathy; the mutations in TNNT2 gene was discovered in two patients with a family history of sudden death, but also with a severe cardiac hypertrophy (MWT z-score≥10). There were no significant differences in clinical or echocardiographic characteristics between patients in whom sarcomeric protein gene mutations were identified and those without mutations, nor differences between individual with 2 mutations and patients with one or no mutations. Conclusions. The search for MYH7, MYBPC3, TNNT2, TNNI3 and TPM1 genes mutations in 39 patients with a diagnosis of early HCM was positive in 33% of cases: unlike in adults HCM in children seems to be more frequently associated with non sarcomeric gene mutation. Furthermore, 7/13 mutations were identified in children <10 years old, suggesting the necessity to perform genetic screening in preteen age.