Aims The review of a case of rare hereditary cardiomyopathy with severe heart failure and unfavourable prognosis.

patients and methods: A boy is the second child in a family; the first child, a girl, died at the age of 2.5 years from chronic heart failure (CHF). No cardiologic observation had been performed until the age of 1.5 years, when the boy suffered from oedema, dyspnea, and wheezing. He was hospitalised and diagnosed with left ventricular non-compaction (LVNC), left ventricular dilatation cardiomyopathy (DCM), reduced myocardial contractility, EF 38%. The therapy of CHF raised EF to 46%–50%.

The molecular genetic testing of the proband was carried by the new-generation sequencing (NGS) method, using cardiac panel including target regions of 404 genes, which mutations are the reason of a cardiac phenotype diseases.

Results The molecular genetic testing of the proband identified the novel homozygous splicing substitution c.559+ 1G>A in the MYL3 gene and heterozygous polymorphism c.649A>G in the MYBPC3 gene. Both the proband’s parents are heterozygous nucleotide substitutions c.559+ 1G>A in the MYL3 gene without clinical manifestations, indicating recessive inheritance of this mutation. The MYL3 gene encodes the myosin cardiac ventricular essential light chain; its mutations are very rare and strongly associated with heart failure and unfavourable prognosis.

During the observed period of 2 years, the therapy of CHF including high doses of diuretics, aldosterone antagonists, ACE inhibitors, b-blockers and digoxin has showed the increase of heart failure.

Conclusion The molecular genetic testing determined the reason of the LVNC and DCM phenotype of a boy, it proved autosomal recessive inheritance of MYL3 gene mutations and also provided effective medical-genetic assistance to the family, including methods of preimplantation genetic diagnosis.