A description of the clinical and genetic characteristics of four Russian patients with Schaaf–Yang syndrome, caused by previously described and newly identified nucleotide variants in MAGEL2 gene, is presented. It was shown that the most severe clinical manifestations were found in a patient with the new identified variant c.1828C>T (p.Gln610Ter), while in a patient with a new nucleotide variant c.1609C>T (p.Gln537Ter) the manifestations of the disease were moderate. Considering the significant similarity of the clinical manifestations of Schaaf–Yang syndrome with Prader–Willi syndrome, the criteria for their differential diagnosis are outlined, the use of which will help optimize the process of molecular genetic analysis aimed at finding the etiologic factor.

TRPV4‑associated neuromuscular diseases represent a clinical spectrum of neuropathies and motor neuron disorders. To date, 3 phenotypic forms are distinguished. There are Charcot–Marie–Tooth disease type 2C, distal hereditary motor neuropathy type 8 (DHMN8), scapulo‑peroneal spinal muscular atrophy (SPSMA). Here we report 3 families with DNMN8 and one family with SPSMA. In all cases, DNA‑analysis revealed single nucleotide variants in the TRPV4 gene previously reported as pathogenic. In 3 probands, a combination of signs of both motor and motor‑sensory neuropathies led to difficulties in the establishment of the clinical diagnosis. Patients had mild sensory disturbances in the feet, but in all of these cases nerve conduction study revealed normal sensory nerve action potentials. Considering the prevailing signs of motor neuropathy, these patients were diagnosed with DNMN8. Clinical signs of sensory disturbances are regarded as not contradicting the diagnosis, since they can be observed in various forms of distal motor neuropathies. The clinical features of SPSMA in one patient corresponded to those previously described in the literature. The involvement of the shoulder girdle muscles and the peroneal muscles and neurogenic changes in needle electromyography allow suspecting SPSMA clinically. A distinctive features of TRPV4‑associated neuromuscular diseases are the vocal cords paresis, sensorineural hearing loss and respiratory failure, however they are not obligatory according to our clinical reports.

BACKGROUND: Achondroplasia and pseudoachondroplasia are hereditary systemic skeletal dysplasias characterized by a certain similarity of clinical manifestations; however, they have different etiopathogenetic mechanisms and confirmation methods for molecular genetic diagnosis. Their common phenotypic features often make differential diagnosis difficult during the clinical examination of patients, planning DNA diagnostics, and appropriate time detection of neurosurgical and orthopedic complications. AIM: This study aimed to identify differential diagnostic criteria for achondroplasia and pseudoachondroplasia and optimize the strategy for their molecular genetic diagnosis. MATERIALS AND METHODS: A comprehensive examination of 76 children from 74 unrelated families aged 1 month to 18 years with phenotypic signs of achondroplasia and pseudoachondroplasia was conducted. To clarify the diagnosis through genealogical and amnestic analysis, clinical and neurological examination data according to the standard method and radiographic data were used. Molecular genetic confirmation of diseases was conducted by searching for hotspot mutations in the FGFR3 gene, assessing the number of GAC repeats located in exon 13 of the COMP gene, and new-generation sequencing of the target panel consisting of 166 genes responsible for hereditary skeletal pathology. RESULTS: Based on a comparative analysis of the specific phenotypic characteristics, the criteria for the differential diagnosis of achondroplasia and pseudoachondroplasia were identified. The leading signs of achondroplasia are disproportionate nanism from birth, macrocrania, and facial dysmorphism, which are not specific to pseudoachondroplasia. Certain radiological features are essential in the differential diagnosis of pseudoachondroplasia, which should be considered when referring to patients for molecular genetic analysis. A deletion of the GAC repeat c.1417_1419del in the COMP gene was identified in 27% of patients with pseudoachondroplasia. Thus, the analyses of these two mutations in FGFR3 and COMP were conducted first. In the absence of target mutations, further diagnostic search should be continued with a target panel consisting of 166 genes responsible for hereditary skeletal pathology or whole-exome sequencing. CONCLUSIONS: The analysis of the clinical, radiological, and molecular genetic characteristics of patients with achondroplasia and pseudoachondroplasia, together with the literature data analysis, made it possible to clarify the differential diagnostic criteria for these diseases and optimize the algorithm for their molecular genetic diagnosis.

Intellectual disability is a widespread group of diseases with population frequency 1–3%. More than half of intellectual disability cases are due to various genetic causes, including monogenic ones. The paper describes three clinical cases of MED13L-associated intellectual disability with an autosomal dominant inheritance. Novel probably pathogenic variants p.Cys118delinsTrpSer and p.Gln2111fs, as well as the previously described p.Pro866Leu mutation in the MED13L gene (NM_015335), were detected in patients by massive parallel sequencing. А rare familial case with two affected maternal half-siblings was of particular interest since the mutation detected in both children was not found in the mother (blood cells and buccal epithelium were investigated). We assume the presence of gonadal mosaicism in the mother, which allows to recommend families with confirmed cases of MED13L-associated intellectual disability to plan pregnancies with prenatal or preimplantational diagnostics. The disease has been shown to have a wide clinical variability, even intrafamilial.

Введение. TRPV4-ассоциированные скелетные дисплазии - группа генетически гетерогенных заболеваний с аутосомно-доминантным типом наследования, обусловленных мутациями в гене TRPV4. Он содержит 16 экзонов и кодирует белок семейства трансмембранных кальциевых каналов. К настоящему времени описано семь нозологических форм этой группы скелетных дисплазий, общая распространенность которых не превышает 1:1 000 000. Основными являются спондилометафизарная дисплазия Козловского (OMIM:184252) и метатропная дисплазия (OMIM:156530). Цель: описание клинико-генетических характеристик российских больных со скелетными дисплазиями, вызванными ранее описанными и впервые выявленными мутациями в гене TRPV4. Методы. Проведено комплексное обследование 15 детей из неродственных семей в возрасте от 10 суток жизни до 15 лет, с клинико-рентгенологическими признаками TRPV4-ассоциированных скелетных дисплазий. Для уточнения диагноза использовались генеалогический анализ, клиническое обследование, неврологический осмотр по стандартной методике с оценкой психоэмоциональной сферы, рентгенография и таргетное секвенирование панели, состоящей из 166 генов, ответственных за развитие наследственной скелетной патологии. Результаты. У 7 пациентов диагностирована спондилометафизарная дисплазия Козловского, у 8 пациентов - метатропная дисплазия. В результате молекулярно-генетического исследования у наблюдаемых нами пациентов идентифицировано 7 патогенных вариантов в гене TRPV4, два из которых обнаружены впервые. Как и у ранее обследованных пациентов, у российских пациентов обнаружены две мажорные мутации в гене TRPV4: p.Arg594His у пациентов со спондилометафизарной дисплазией Козловского и p.Pro799Leu у пациентов с метатропной дисплазией. Заключение. Полученные результаты в совокупности с данными литературы позволяют высказать предположение о целесообразности создания системы для скрининга мажорных мутаций у пациентов со спондилометафизарной дисплазией Козловского и метатропной дисплазией, имеющих сходные клинико-рентгенологические проявления. Первоочередное использование такой системы позволит оптимизировать процесс молекулярно-генетической диагностики этих заболеваний. Introduction. TRPV4 -associated skeletal dysplasias are a genetically heterogeneous group of autosomal dominant disorders caused by mutations in the TRPV4 gene. TRPV4 contains 16 exons and encodes a Ca2+-permeable transmembrane channel protein. To date, seven nosological forms within this group of skeletal dysplasias have been described. The overall prevalence of these disorders does not exceed 1:1,000,000. The most frequent forms among this group are spondylometaphyseal dysplasia, Kozlowski type (OMIM:184252) and metatropic dysplasia (OMIM:156530). Objective: to describe the clinical and genetic characteristics of Russian patients with skeletal dysplasia caused by previously reported and newly identified mutations in the TRPV4 gene. Methods. A comprehensive examination of 15 children from unrelated families aged 10 days-15 years with clinical and radiological signs of TRPV4-associated skeletal dysplasia was carried out. To specify diagnosis we used genealogical analysis, clinical examination, neurological examination according to a standard method with an assessment of the psycho-emotional sphere, radiography and sequencing a targeted gene panel including 166 genes responsible for the development of hereditary skeletal disorders. Results. Spondylometaphyseal dysplasia, Kozlowski type was diagnosed in 7 and metatropic dysplasia in 8 patients. 7 pathogenic variants in the TRPV4 gene were identified, of which two were novel. As in previously reported cases, two major mutations in the TRPV4 gene were found in Russian patients: p.Arg594His in patients with spondylometaphyseal dysplasia, Kozlowski type and p.Pro799Leu in patients with metatropic dysplasia. Conclusion. Our findings combined with previously reported results suggest the rationale for creating a genetic screening test to detect major mutations in patients with spondylometaphyseal dysplasia, Kozlowski type and metatropic dysplasia, which have similar clinical and radiological manifestations. Foremost use of this test will improve the molecular diagnostics of these diseases.

OBJECTIVE:To estimate the proportion and spectrum of infrequent autosomal dominant spastic paraplegias in a group of families with DNA-confirmed diagnosis and to investigate their molecular and clinical characteristics.MATERIAL AND METHODS:Ten families with 6 AD-SPG: SPG6 (n=1), SPG8 (n=2), SPG9A (n=1), SPG12 (n=1), SPG17 (n=3), SPG31 (n=2) were studied using clinical, genealogical, molecular-genetic (massive parallel sequencing, spastic paraplegia panel, whole-exome sequencing, multiplex ligation-dependent amplification, Sanger sequencing) and bioinformatic methods.RESULTS AND CONCLUSION:Nine heterozygous mutations were detected in 6 genes, including the common de novo mutation p.Gly106Arg in NIPA1 (SPG6), the earlier reported mutation p.Val626Phe in WASHC5 (SPG8) in isolated case and the novel p.Val695Ala in WASHC5 (SPG8) in a family with 4 patients, the novel mutation p.Thr301Arg in RTN2 (SPG12) in a family with 2 patients, the novel mutation c.105+4A>G in REEP1 (SPG31) in a family with 4 patients and the reported earlier p.Lys101Lys in REEP1 (SPG31) in a family with 3 patients, the known de novo mutation p.Arg252Gln in ALDH18A1 (SPG9A) in two monozygous twins; the common mutation p.Ser90Leu in BSCL2 (SPG17) in a family with 3 patients and in isolated case, reported mutation p.Leu363Pro in a family with 2 patients. SPG6, SPG8, SPG12 and SPG31 presented 'pure' phenotypes, SPG31 had most benign course. Age of onset varied in SPG31 family and was atypically early in SPG6 case. Patients with SPG9A and SPG17 had 'complicated' paraplegias; amyotrophy of hands typical for SPG17 was absent in a child and in an adolescent from 2 families, but may develop later.

Background. Lissencephaly (LIS) is a spectrum of malformations of the cerebral cortex that occur as a result of impaired migration of neuronal precursors to the cortical plate and the formation of furrows and convolutions in the post‑migration period of embryonic development. In recent years, a significant role of hereditary factors in the occurrence of LIS has been shown due to the improvement of methods of molecular genetic diagnostics. Today, 13 genetic variants have been identified in the LIS group, six of which are inherited autosomal recessively, five are autosomal dominant, and two are linked to the X chromosome. It is shown that 80 % of cases of hereditary LIS is caused by mutations in two genes: PAFAH1B1, which is responsible for the occurrence of the LIS 1 type with an au‑ tosomal dominant type of inheritance, and in the DCX gene, localized on the X chromosome. The rest of the genetic variants account for from 1 % to 5 % of cases of defects accompanied by dysgenesis of the cerebral cortex. In recent years, the number of works devoted to the analysis of clinical and genetic characteristics of monogenic variants of LIS has increased. The results of such studies will allow us to improve our understanding not only of the pathogenetic mechanisms of this group of diseases, but also of the molecular basis for the formation of brain structures in the normal embryonic period.Objective: to describe the clinical and genetic characteristics of three Russian patients with autosomal dominant LIS type 3 (OMIM: 611603) caused by mutations in the TUBA1A gene.Materials and methods. All patients were under observation in the consultative and diagnostic department of Research Centre for Medical Genetics. The diagnosis was established on the basis of clinical data, genealogical anamnesis, results of brain MRI, EEG night video monitoring and exome sequencing by NGS. The validation of the identified nucleotide substitutions and analysis of the disease segregation were performed using the Sanger direct automatic sequencing method.Results. The clinical and genetic characteristics of three patients with newly identified and previously described mutation in the TUBA1A gene were analyzed. Possible effects of new missense mutations in the gene on the function of the protein product of the gene are discussed.Conclusions. The results of the analysis of the clinical and genetic characteristics of the patients we observed contribute to the study of the polymorphism of clinical manifestations resulting from mutations in the TUBA1A gene. The previously stated assumption about a wide range of malformations of the brain in patients with mutations in this gene was confirmed, which should be taken into account when making a diagnosis.

Introduction. Limb-girdle muscular dystrophy (LGMD) includes more than 30 forms caused by mutations in genes located on autosomes. The most common form is calpain-3-related LGMD, with autosomal recessive inheritance pattern (OMIM 253600). An autosomal dominant form of LGMD (OMIM 618129) caused by c.643_663del heterozygous mutation in the CAPN3 gene is also supposed to exist. This article describes a family case of LGMD caused by mutations in the CAPN3 gene with pseudodominant inheritance. Materials and methods. Two patients with LGMD were studied: a 59-year-old woman and her 38-year-old daughter. Clinical, genealogical and molecular genetics methods were used: limb girdle muscular dystrophy MPS panel, Sanger sequencing of DNA of the proband, her affected daughter, and six first- and second-degree relatives across four generations. Results. It was found that identical variants of the nucleotide sequence, c.598_612del and c.1746-20CG, identified in the CAPN3 gene of the proband and her daughter, are in the trans position (compound heterozygous state), causing autosomal recessive calpain-3-related LGMD. This is an example of an incredibly rare pseudodominant inheritance of an autosomal recessive disease, established through indirect evidence that the probands husband is a heterozygous carrier of a nucleotide substitution in the CAPN3 gene. Conclusion. It is crucial to examine the marriage partner for heterozygous carrier status of a gene mutation responsible for the disease in family planning and when clarifying the childs prognosis for a patient with an autosomal recessive disease. Considering the existence of a late-onset (after 30 years) LGMD phenotype associated with the CAPN3 gene, differential diagnosis should begin with testing this gene in families with late disease onset.

Синдром Сотоса представляет собой редкое аутосомно-доминантное заболевание с частотой встречаемости около 1:14000 новорожденных. Несмотря на ряд характерных клинических проявлений, его диагностика затруднена в связи с высокой степенью перекрывания фенотипа с рядом других наследственных синдромов, таких как синдром Видемана-Беквита или синдром Марфана. Молекулярно-генетической причиной синдрома Сотоса являются мутации в гене NSD1, приводящие к дисфункции белка. В статье представлены и охарактеризованы варианты в гене NSD1, найденные в ходе диагностики методами высокопроизводительного параллельного секвенирования (NGS) и MLPA. Sotos syndrome is a rare autosomal dominant disorder with an incidence of about 1 in 14,000 newborns. Despite a number of characteristic clinical manifestations, its diagnosis is difficult due to the high degree of overlap of the phenotype with a number of other hereditary syndromes, such as Beckwith-Wiedemann syndrome or Marfan syndrome. The molecular genetic cause of Sotos syndrome is mutations in the NSD1 gene, leading to protein dysfunction. The article presents and characterizes variants in the NSD1 gene found during diagnostics using high-throughput sequencing (NGS) and MLPA.

Microcephaly-capillary malformation syndrome (MICCAP: OMIM 614261) is a severe monogenic disorder inherited in an autosomal recessive manner caused by mutations in the STAMBP gene. There are less than 20 published cases of the syndrome to date. The paper reports three new cases of rare MICCAP syndrome. The cause of the disorder was confirmed in three affected individuals from two unrelated families by pedigree analysis, biochemical analysis, RFLP analysis and automated Sanger sequencing. The two brothers were homozygous for the potentially pathogenic STAMBP gene variant c.188A>G (p.Tyr63Cys). Clinical phenotype of the girl from the second family resulted from the combination of two genetic disorders: galactosemia caused by the compound heterozygosity for the pathogenic GALT gene variants (c.563A>G and c.855G>T), and MICCAP caused by the STAMBP gene variants (c.204-5c>g and с.668_669delCA), one of which originated de novo. The prevalence of microcephaly-capillary malformation syndrome in Russia is evaluated, it is one per 120,000 people (CI: 1/356 724–1/62 691). The carrier frequency is one per 173 people. The target STAMBP gene analysis makes the genetic confirmation of the MICCAP syndrome quicklier. When determining the tactics of diagnosis and therapy in each particular case, the possibility of combination of two rare genetic disorders in one patient should be considered.

Идентификация причин формирования аномалий развития у пациентов со сбалансированными хромосомными перестройками на сегодняшний день является актуальным и не в полной мере изученным направлением в цитогенетической практике, требующим разработки уникального подхода с использованием современных молекулярно-генетических технологий. Целью данного исследования явилась этиологическая диагностика геномного дисбаланса у пациентов со сбалансированными хромосомными перестройками и аномалиями развития. 20 пациентов с аномальным фенотипом и сбалансированными хромосомными перестройками, выявленными при стандартном кариотипировании, были обследованы методами хромосомного микроматричного анализа (ХМА) и FISH. Геномный дисбаланс (CNV) обнаружен в 13 случаях из 20, что составило 65%. Использование ХМА позволило установить, что в 69,2% случаев носительства сбалансированных хромосомных перестроек причиной аномального фенотипа являлось наличие микроделеций/микродупликаций, ассоциированных с точками разрывов при перестройках, а в 20,8% случаев наблюдались микроделеции/микродупликации на хромосомах, не задействованных в аберрациях. Несмотря на то, что ХМА позволил выявить причины аномалий развития в большинстве случаев, 7 пациентам (35%) не удалось установить окончательный молекулярно-цитогенетический диагноз. Более того, у некоторых пациентов выявленные CNVs не полностью отражают генотип-фенотип корреляцию, что требует проведения дополнительных молекулярно-генетических исследований. При отсутствии геномного дисбаланса при ХМА, а также при неполной генотип-фенотип корреляции, диагностика этиологии аномалий развития и патологического фенотипа должна быть продолжена молекулярными методами более высокого разрешения. Identification of genomic imbalances in cases with balanced chromosomal rearrangements and abnormal phenotype is a current trends in cytogenetics practice, requiring the development of unique approach using modern molecular genetic technologies. The aim of this study is diagnostics etiologies of the abnormal phenotype in patients with balanced chromosomal rearrangements. We report the investigations results of 20 patients with abnormal phenotype and balanced chromosomal rearrangements by conventional cytogenetic analysis. Genomic imbalances by microarray studies detected in 13 of 20 cases (65%). Most of CNVs was microdeletion or microduplication at a rearrangement breakpoint (69.2%) and 20.8% microdeletion/microduplication in other chromosomes.

Identification of genomic imbalances in cases with balanced chromosomal rearrangements and abnormal phenotype is a current trends in cytogenetics practice, requiring the development of unique approach using modern molecular genetic technologies. The aim of this study is diagnostics etiologies of the abnormal phenotype in patients with balanced chromosomal rearrangements. We report the investigations results of 20 patients with abnormal phenotype and balanced chromosomal rearrangements by conventional cytogenetic analysis. Genomic imbalances by microarray studies detected in 13 of 20 cases (65%). Most of CNVs was microdeletion or microduplication at a rearrangement breakpoint (69.2%) and 20.8% microdeletion/microduplication in other chromosomes.

Синдром микроцефалии в сочетании с капиллярными мальформациями (MICCAP) (OMIM #614261) — тяжелое моногенное заболевание с аутосомно-рецессивным типом наследования, причиной которого являются мутации гена STAMBP. На сегодняшний день в мировой литературе описано менее 20 случаев данного синдрома. В работе представлены три новых случая редкого синдрома MICCAP: на основании клинико-генеалогического анализа, методов биохимического исследования, анализа полиморфизма длин рестрикционных фрагментов, прямого автоматического секвенирования по Сенгеру установлена причина болезни у трех больных из двух неродственных семей. У двух братьев выявлен вероятно-патогенный вариант гена STAMBP c.188A>G (p.Tyr63Cys) в гомозиготном состоянии. У девочки из второй семьи причиной клинического фенотипа явилось сочетание двух наследственных заболеваний: галактоземии, обусловленной патогенными вариантами c.563A>G и c.855G>T гена GALT в компаунд-гетерозиготном состоянии и MICCAP, обусловленного вариантами c.204-5c>g и с.668_669delCA гена STAMBP, один из которых возник de novo. Оценены частота синдрома микроцефалии в сочетании с капиллярными мальформациями в России — один случай на 120 000 человек (ДИ: 1/356 724–1/62 691) и частота носительства данного синдрома — один случай на 173 человека. Исследование гена STAMBP позволяет быстро найти молекулярно-генетическую причину синдрома MICCAP. При выборе тактики диагностики и терапии в каждом конкретном случае необходимо учитывать возможность сочетания у одного больного двух редких наследственных патологий.

Background Spastic paraplegia type 30 (SPG30) caused by KIF1A mutations was first reported in 2011 and was initially considered a very rare autosomal recessive (AR) form. In the last years, thanks to the development of massive parallel sequencing, SPG30 proved to be a rather common autosomal dominant (AD) form of familial or sporadic spastic paraplegia (SPG),, with a wide range of phenotypes: pure and complicated. The aim of our study is to detect AD SPG30 cases and to examine their molecular and clinical characteristics for the first time in the Russian population. Methods Clinical, genealogical and molecular methods were used. Molecular methods included massive parallel sequencing (MPS) of custom panel ‘spastic paraplegias’ with 62 target genes complemented by familial Sanger sequencing. One case was detected by the whole -exome sequencing. Results AD SPG30 was detected in 10 unrelated families, making it the 3rd (8.4%) most common SPG form in the cohort of 118 families. No AR SPG30 cases were detected. In total, 9 heterozygous KIF1A mutations were detected, with 4 novel and 5 known mutations. All the mutations were located within KIF1A motor domain. Six cases had pure phenotypes, of which 5 were familial, where 2 familial cases demonstrated incomplete penetrance, early onset and slow relatively benign SPG course. All 4 complicated cases were caused by novel mutations without familial history. The phenotypes varied from severe in two patients (e.g. lack of walking, pronounced mental retardation) to relatively mild non-disabling symptoms in two others. Conclusion AD SPG30 is one of the most common forms of SPG in Russia, the disorder has pronounced clinical variability while pure familial cases represent a significant part.

Синдром «Блефарофимоз-птоз-обратный эпикант» (БПЭС) - заболевание, характеризующееся пороками развития век: птозом, блефарофимозом и наличием обратного эпиканта или телеканта. БПЭС у женщин может сопровождаться синдромом преж-девременного истощения яичников и связанным с ним бесплодием. В настоящей работе суммированы результаты генетического исследования 24 больных из 19 неродственных семей с направительным диагнозом БПЭС. В результате анализа всей кодирующей последовательности гена FOXL2 мутации выявлены в 10 неродственных семьях Blepharophimosis-Ptosis-Epicanthus inversus syndrome (BPES) is a disease characterized by malformations of the eyelids: ptosis, blepharophimosis and the presence of a reverse epicant or telecant (BPES). This syndrome in women can be accompanied by a premature ovarian exhaustion syndrome and related infertility. This work summarizes the results of FOXL2 gene analysis for 24 patients from 19 unrelated families with an incoming diagnosis. Mutations were detected in 10 unrelated families

Актуальность. Нейрофиброматоз первого типа является одним из наиболее распространенных моногенных заболеваний. Этиологическим фактором его развития является патогенная мутация в гене NF1. Однако у части пациентов не удается достичь молекулярно-генетического подтверждения клинического диагноза. Мы полагаем, что в некоторых случаях это может быть обусловлено соматическим мозаицизмом с малой долей клеток, несущих патогенный аллель, в анализируемом образце биологического материала. Аллели с низкой представленностью отсеиваются общепринятыми фильтрами программного обеспечения при поиске генетических вариантов методом высокопроизводительного параллельного секвенирования (ВПС) и/или не детектируются визуально за счет слияния с фоновым шумом при анализе результатов секвенирования по Сэнгеру. Цель. Поиск патогенных мозаичных генетических вариантов у пациентов с нейрофиброматозом первого типа без выявленных стандартными методами герминальных мутаций в гене NF1. Материалы и методы. Исследование проведено на материале ДНК лимфоцитов периферической крови 275 пациентов, объединенных клиническим диагнозом нейрофиброматоз первого типа и отсутствием герминальных мутаций в генах NF1 и NF2 по результатам стандартных лабораторных исследований. Поиск точковых мутаций осуществляли методом ВПС на платформе Ion Torrent. Дизайн панели праймеров включал экзоны, прилегающие к ним интронные сегменты (20-70 п.н.), а также 3’UTR и 5’UTR генов NF1 и NF2. Исключение протяженных делеций в NF1 и NF2 осуществляли методом MLPA. С целью поиска мозаичных генетических вариантов был разработан и проведен углубленный анализ данных ВПС, основанный на биоинформатических и статистических подходах. Для верификации выявленных мозаичных патогенных генетических вариантов использовали секвенирование ДНК по Сэнгеру и гетеродуплексный анализ. Результаты. Патогенные соматические мутации в гене NF1 выявлены в 12 из 275 образцов (4,4%) ДНК больных, у которых были исключены герминальные мутации. В 8 образцах наличие мутантного аллеля было подтверждено альтернативными методами. Выводы. ДНК-диагностика доминантно наследуемых заболеваний требует особых подходов, учитывающих явление соматического мозаицизма. Предложенный метод позволяет выявить генетические варианты, представленные с малой аллельной частотой, без увеличения глубины секвенирования исследуемого образца и может быть применен для ретроспективного анализа данных ВПС с целью повышения качества ДНК-диагностики. 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.

Background. In cases of neurofibromatosis type 1 and type 2, pathogenic mutations are distributed evenly along the coding regions of the NF1 and NF2 genes. Herewith, in more than 50% of cases, the disease is the result of a de novo mutation. Therefore, the search for a causative mutation is particularly time-consuming and the catalogs of pathogenic and non-pathogenic genetic variants are an indispensable assistance handbook for geneticists in their work. Objective. To determine the spectrum of genetic alterations in Russian neurofibromatosis patients and to characterize novel pathogenic mutations and rare non-pathogenic genetic variants in the NF1 and NF2 genes. Material and methods. The study was carried out on the peripheral blood lymphocyte and/or tumor tissue DNA samples from 617 patients. NGS was performed on the Ion Torrent PGM and Ion Torrent S5 sequencing machines using NF1 and NF2 AmpliSeq gene panel. Gene panel encompasses exons of the NF1 and NF2 genes, adjacent intron segments (20-70 bp), 3’UTRs, and 5’UTRs. Sanger sequencing was used to verify pathogenic genetic variants and the MLPA method was used to search for NF1 and NF2 gross deletions. Result. Complex molecular genetic diagnostics of the NF1 and NF2 alterations was accomplished for 617 patients. The NF1 and NF2 mutations were detected in 303 and 19 cases, respectively. Conclusion. We have characterized 69 novel pathogenic mutations, 68 in the NF1 gene, and 1 in the NF2 gene, as well as 68 rare non-pathogenic genetic variants. Most non-pathogenic genetic variants are represented by synonymous SNPs and nucleotide substitutions in untranslated regions, which are particularly difficult to interpret during medical-genetic counseling.