Compliance with ethical standards: the study was approved by the Ethics Committee of the Research Centre for Medical Genetics (protocol № 5/8 dated November 12, 2018). The informed consent to molecular genetic testing, and anonymity-preserving clinical and molecular genetics data publishing (including photos and videos) was submitted by all participants or their legal representatives.

Author contribution: Shchagina OA — study design, molecular genetic analysis, frequency estimation, statistical analysis; Semenova NA, Bessonova LA — clinical examination and genetic counseling of the patients’ families; Larshina EA — biochemical assays, GALT gene analysis; Beskorovainiy NS — exome sequencing data processing; Zakharova EYu — biochemical analysis, prevalence calculation; Ryzhkova OP — pathogenicity analysis of genetic variants, exome sequencing; Poliakov AV — selection of primers for molecular genetic analysis.