Background. Neurofibromatosis type 1 is one of the most common monogenic disorders. A pathogenic mutation in NF1 is the etiological factor of neurofibromatosis type 1. Nevertheless, not all patients receive molecular genetic verification of the clinical diagnosis. We believe that this may be due to a somatic mosaicism with a small fraction of pathogenic allele, which is neglected by the NGS analysis software and/or is undetectable by Sanger sequencing due to noisy background. Objective. To detect pathogenic mosaic mutations in cases of neurofibromatosis type 1 without germline genetic variants. Material and methods. Two hundred seventy five peripheral blood lymphocyte DNA samples from patients with NF1 and without germline mutation were retrospectively analyzed. DNA samples were sequenced with Ion PGM and Ion S5 NGS systems. Gene panel design included NF1 and NF2 genes: exons, adjacent intron segments (20-70 b.p.), 3’UTRs and 5’UTRs. Samples were also tested using MLPA in order to exclude deletions in NF1 and NF2. We developed and implemented the pipeline to search mosaic cases using bioinformatics approaches. All newly detected mutations were evaluated by Sanger sequencing and by heteroduplex analysis. Result. We have identified new pathogenic mutations in NF1 for 12 patients (4.4%) and verified 8 of them using alternative methods. Conclusion. Dominant disorders, like neurofibromatosis type 1, require a detailed bioinformatic analysis of NGS results with respect to somatic mosaicism. Our approach makes it possible to identify genetic variants with low representation of a pathogenic allele without increasing the sequencing depth of the sample under study and can be used for retrospective analysis of NGS data in order to improve the quality of DNA diagnostics.

Genetic epidemiological study of the population of the North Ossetia-Alania Republic, Russia, is caring out by the Laboratory of Genetiс Epidemiology of Research Centre for Medical Genetics (Moscow, Russia).Within the framework of the standard protocol we study the maximum of possible population-genetic characteristics. Based on the 27583 marriage records, the index of endogamy, the intensity of metisation and ethnic marriage assortativness in 8 regions of North Ossetia and Vladikavkaz have been analyzed. The differences in the marriage and migration characteristics are revealed for two subethnoses: the Irons and the Digors. The Digors have a higher value of endogamy index and a lower metisation level than the Irons have.

The Working group of Russian Society of Medical Geneticists prepared these Recommendations based on General Guidelines and Quality Assurance for Cytogenetics: a common European framework for quality assessment for constitutional,acquired and molecular cytogenetic investigations (European Cytogeneticists Association (E.C.A.) Permanent Working Group for Cytogenetics and Society). This document is devoted to prenatal and postnatal (molecular) cytogenetic diagnosis of the constitutional chromosomal abnormalities, is aimed to define quality framework and to improve the activity of cytogenetic laboratories in Russian Federation. The Recommendations include aspects of quality control and safety for most of the methods currently employed by cytogenetic laboratories.

Introduction. Mucolipidosis II alpha/beta (ML IIA/B) is a rare autosomal recessive disorder from the group of lysosomal storage diseases. This is a slowly progressive multisystem pathology, which is manifested from birth and leads to the death of patients in early childhood. Here we report two cases of mucolipidosis II A/B due to homozygous p. Arg375X mutation in GNPTAB gene. Patients and methods. Patient 1 was first examined by a geneticist at the age of 9 days. Мicrocephaly, brachycephaly, craniofacial dysmorphiс features, funnel chest, hernia the white line of the abdomen, inguinal hernia, shortening and deformity of the shoulder bones, the excess folds of skin in the shoulder area, long fingers, shortening and deformity of hips, severe varus and saber deformity of the shins, fracture, pronounced folds of the skin on the thighs, heel feet, hepatomegaly were mentioned. Laboratory examination revealed thrombocytopenia and significant increase of lysosomal enzymes activity in plasma and ML II was diagnosed. At the age of 3 years and 4 months, the boy presents severe growth and psychomotor development retardation, every month he suffers from acute respiratory diseases. Dry skin, hypertrichosis of the back, shoulders, neck, craniofacial dysmorphism, short neck, barrel chest, thickening of the wrist and ankle joints, restriction of mobility of large joints, wide hands, limiting extension of the interphalangeal joints, diastasis of direct abdominal muscles, bilateral inguinal-scrotal hernia, aortic and mitral valves dysfunction, partial atrophy of the optic nerves were found. Patient 2 was first examined by a geneticist at the age of 9 months due to short stature and psychomotor development retardation. The diagnosis of ML II was made one year later. At 1 year and 10 months, the boy had global developmental delay, coarse facial features, short neck, short chest, thoracolumbic kyphosis, limited mobility in large joints, wide hands and feet, brachydactyly and camptodactyly, aortic dilatation, dysfunction of the aortic valves, mitral valve insufficiency of the 2nd degree with signs of volume overload of the left atrium; dysplasia of the left ventricle cavity and a decrease in myocardial contractility. The child often suffered from respiratory infections, which were twice accompanied by pulmonary cardiac decompensation and pulmonary edema. The boy’s life span was 3 years and 2 months. Molecular genetic studies for the search for mutations in the GNPTAB gene were performed for patient 1 and his parents, as well as for parents and healthy siblings of patient 2. The nucleotide sequence of the GNPTAB gene was analyzed by direct sequencing on an ABI 3500 automated analyzer. Results and discussion. Patient 1 turned out to be a homozygous carrier of the p.Arg375X mutation in the tenth exon of the GNPTAB gene; this allele was found in its parents in the heterozygous state. Parents of patient 2 turned out to be heterozygous carriers of the p.Arg375X mutation. Thus, the boy was obviously a homozygous carrier of this mutation. Despite the same genotype, significant differences in the course of the disease in the described patients are evident: in patient 1, the disease manifested from birth with severe dysmorphia and skeletal deformities, but the heart function remained compensated, and the first signs of valvular lesions were detected only at the age of three years and four months. The severity of the patient’s 2 condition, on the contrary, was due to increasing heart failure due to early damage to the valvular apparatus of the heart, which led to the death of the child. Conclusion. ML IIA/B is a severe progressive disease characterized by variable clinical manifestations and course of the pathological process even in patients with the same genotype. Life expectancy for ML IIA/B is determined, in accordance with our experience, by the degree of damage of the cardiovascular system. Neither the age of appearance of the first signs of the disease, nor the severity of bone pathology, are predictors of the rate of disease progression and life expectancy in patients with ML IIA/B.

Introduction Baraitser-Winter Syndrome (BWCFF) is a very rare autosomal dominant hereditary disease caused by mutations in the ACTB and ACTG1 genes. Almost all known cases of this disease are caused by de novo missense mutations in the ACTB and ACTG1. In this paper we present a new case of BWCFF syndrome, due to p.Ile136Val mutation in the ACTB gene. Patients and methods. Proband - a boy, 6 years 8 months, out of twins. The patient’s phenotype was analyzed using the Face2Gene application. Direct sequencing of 1-4 exons and the adjacent intron sequences of the ACTB gene was performed in proband and all members of his family. Results. The proband has characteristic symptoms of BWCFF: postnatal borderline microcephaly, facial dysmorphism, iris colobomas of both eyes, short, webbed neck, epilepsy, congenital heart defect. Unlike most cases of the syndrome the patient does not have developmental delay and gross changes in the cortex or other structures of the brain. ACTB gene sequencing resulted in detection of heterozygous missense mutation p.406A> G (p.Ile136Val, rs1554329352) in proband. This mutation was not found in his parents and healthy siblings. Conclusion The use of modern phenotyping technologies allowed us to suggest the correct clinical diagnosis, to conduct an effective targeted search for mutations in the ACTB gene and diagnose a new case of BWCFF syndrome.