This article presents the case of a combination of two genetically determined diseases in one early age patient: long QT syndrome type 1 and mucopolysaccharidosis type IIIA.

Arrhythmogenic cardiomyopathy is a genetically determined disease of the heart muscle, characterized by fibrofat replacement of the ventricular myocardium, which predisposes to ventricular arrhythmias and a high risk of SCD. Initially, it was believed that this disease is characterized by an exclusive or predominant lesion of the right ventricle. However, fibro-fatty replacement can also be localized in the left ventricle without involvement of the right chambers. This article presents a rare clinical case of a child with Carvajal syndrome with the classic triad of signs (left-dominant form of AСM, keratoderma, and woolly-curly hair).

Atrial fibrillation is the most common persistent arrhythmia in adults; however, it is quite rare in children. In patients without structural heart diseases or extracardiac causes, the genetic basis of the arrhythmia can be assumed. A clinical case of atrial fibrillation in a child, probably associated with the variant D1907H in the SCN10A gene, was described in this article. In spite of a very limited clinical and genetic information on the association of Nav 1.8 channel encoded by SCN10A with atrial arrhythmias, the presented case can further confirm the role of this gene in arrhythmogenesis in children.