[Molecular genetic analysis of hereditary neurodegenerative diseases]. / Molekuliarno-geneticheskii analiz nasledstvennykh neirodegenerativnykh zabolevanii.

The review summarizes the results of a decade of molecular genetic studies of several high-incidence hereditary neurodegenerative diseases, including primary parkinsonism, various forms of hereditary dystonia and ataxia, polyglutamine disorders, hepatolenticular degeneration, essential tremor, etc. Various relevant mutations were studied. The character and frequencies of particular mutations and the corresponding genetic disorders were established for the Russian population. Particular genotypes were associated with various clinical variants of the diseases. Genetic loci were identified for several unique hereditary diseases of the nervous system (X-linked cerebellar hypoplasia, an atypical form of autosomal recessive muscular dystrophy, etc.). Nosological positions of the relevant clinical forms were clarified on the basis of the molecular genetic data. Protocols were developed for direct or indirect DNA diagnostics of the diseases under study to improve medical genetic counseling and prevention of new disease cases in affected families.

[Molecular genetic analysis of essential tremor]. / Molekuliarno-geneticheskii analiz éssentsial'nogo tremora.

Essential tremor (ET) is the most common extrapyramidal disorder of the central nervous system with autosomal dominant transmission in the majority of cases and age-dependent penetrance of the mutant gene. In a number of cases, it shares some phenotypic features with autosomal dominant idiopathic torsion dystonia (locus DYT1 on chromosome 9q32-34) and is genetically heterogeneous: distinct variants of ET were mapped to chromosomes 3q13 (ETM1) and 2p22-25 (ETM2). We performed studies of candidate loci in a group of Slavonic (11 patients) and Tajik (19 patients) families with ET. Mutational analysis of the DYT gene in probands did not reveal the major deletion 946-948delGAG characteristic of idiopathic torsion dystonia, which allows one to genetically distinguish the studied hereditary forms of ET and torsion dystonia. Based on analysis of genetic linkage in informative Tajik pedigrees with ET, linkage to locus ETM1 on chromosome 3q13 was established in four families. Maximum pairwise Lod score was 2.46 at recombination fraction of theta = 0.00; maximum combined multipoint Lod score was 3.35 for marker D3S3720 and a common "mutant" haplotype for markers D3S3620, D3S3576, and D3S3720 allowed us to locate a mutant gene in a relatively narrow chromosome region spanning 2 cM. In one informative pedigree with ET, both candidate loci ETM1 and ETM2 were definitely excluded on the basis of negative Lod scores obtained by linkage estimations, which testifies to the existence of another distinct gene for autosomal dominant ET.

[Molecular-genetic analysis of torsion dystonia in Russia]. / Molekuliarno-geneticheskii analiz torsionnoi distonii v Rossii

For the first time in Russia, analysis of the GCH-I and DYT1 genes was carried out for the purpose of direct DNA diagnostics in families with various forms of hereditary torsion dystonia (TD). Four new missense mutations (Met102Lys, Thr94Lys, Cys141Trp, and Ser176Thr) in the GCH-I gene were found in patients with dopa-responsive dystonia (DRD), testifying to a genetic heterogeneity of this clinical form of TD. The distribution of the major del GAG mutation in exon 5 of the DYT1 gene was studied in patients with non-dopa-responsive dystonia (NDRD). In total, the mutation was found in 68% of the patients. The frequency of this mutation in Ashkenazi Jews with NDRD was 100% (twice higher than in Slavonic families), suggesting the founder effect reported for NDRD in this ethnic group. Mutations of the GCH-I and DYT1 genes were also found in patients with atypical and questionable cases of TD, which are difficult to diagnose with methods other than DNA analysis. The data obtained made it possible to extend the spectrum of clinical signs of DRD and NDRD and to revise the views on true penetrance of the corresponding mutant genes, which is important for medical genetic counseling in affected families.

A common 3-bp deletion in the DYT1 gene in Russian families with early-onset torsion dystonia.

Hereditary torsion dystonia represent a clinically and genetically heterogeneous group of movement disorders. The most severe and frequent form of hereditary torsion dystonia is early-onset generalized dystonia, DYT1. The DYT1 gene (Ozelius et al., 1997) encodes an ATP-binding protein torsin A. A unique 3-bp deletion (GAG) was found in the heterozygous state in almost all patients with early-onset dystonia from different populations. We observed 39 patients with early-onset generalized torsion dystonia belonging to 22 families from Russia. Seven families were of Ashkenazi Jewish (AJ) ethnic background, and other patients originated from the Slavonic population of Russia. The GAG deletion was identified in 24 affected persons from 15 families (68.2% of the families studied). In all the 7 families of AJ origin the disease was found to be caused by the deletion. In Slavs, the deletion was identified in 8 of 15 families (53%). In two deletion-positive families we observed the co-occurrence of typical early-onset generalized dystonia and atypical phenotypes-either isolated postural hand tremor or stutter.

A novel mutation in the GTP cyclohydrolase I gene associated with a broad range of clinical presentations in a family with autosomal dominant dopa-responsive dystonia.

We examined a large family of Ashkenazi Jewish origin with autosomal dominant dopa-responsive dystonia (DRD). Mutation analysis of the GTP cyclohydrolase I gene revealed in affected members a novel point mutation (a C/A change in exon 1) resulting in a threonine-to-lysine substitution at residue 94. The mutation was characterized by variable expressivity and was associated with either a 'classical' DRD phenotype or various atypical phenotypes, such as subtle transitory equinovarus postures of the feet or isolated hand tremor. This observation demonstrates the significance of the molecular testing in establishing the clinical diagnosis of DRD.

[Friedreich's disease: a real spectrum of clinical manifestations in terms of direct DNA diagnosis]. / Bolezn' Fridreikha: istinnyi spektr klinicheskikh proiavlenii v svete vozmozhnostei priamoi DNK-diagnostiki.

Friedreich's disease (FD) is autosomal-recessive form of hereditary ataxias conditioned by expansion of the trinucleotide GAA-repetitions in a new X25 gene. The study was performed in 20 patients from 13 families of different ethnic origin (Slavs, Turkmen, Moldavians, etc) with a suspicion to FD as well as in their 24 relatives who were clinically healthy. Direct DNA-diagnosis confirmed FD diagnosis in patients from 11 families; besides, a number of GAA-repetitions in the patients was in the range from 100 till 1200 (680 +/- 350). A molecular analysis revealed that FD severity was determined by a character of the mutation in each case: a classic form of the disease was characterized by the highest degree of the expansion of GAA-repetitions (more than 400), meanwhile atypic FD cases with late debut and slow progression were conditioned by either a small degree of the expansion of GAA-repetitions or by the presence of point mutations in one of the gene's alleles. A direct DNA-diagnosis permitted to determine a heterozygous carriage of the mutation in 3 clinically healthy individuals. Such cases are necessary to take into consideration in medico-genetic consultations.

The GTP cyclohydrolase I gene in Russian families with dopa-responsive dystonia.

OBJECTIVE: To search for mutations in the GTP cyclohydrolase I (GCH-I) gene in a set of Russian families with dopa-responsive dystonia (DRD). DESIGN: Six large families with 54 affected family members and 2 patients with sporadic DRD were examined. Mutation screening was performed using single-strand conformation polymorphism analysis followed by direct sequencing of the presumably mutated exons, in patients whose results showed a normal pattern on single-strand conformation polymorphism analysis, the entire coding region of the GCH-I gene was sequenced. RESULTS: Three new heterozygote point mutations located within exons 1, 2, and 4 of the GCH-I gene were identified in 3 families with autosomal-dominant inheritance. All these mutations are predicted to cause amino acid changes in the highly conserved regions of the gene. In patients from 3 other families and in both patients with sporadic DRD, no alterations in the translated portion of the GCH-I gene were observed. CONCLUSIONS: Mutations in the coding region of the GCH-I gene account for a significant fraction (up to half) of the patients with a typical clinical picture of DRD. None of the mutations in the GCH-I gene described so far were detected more than once, which precludes the possibility of creating simple DNA testing procedures for routine clinical practice.

[Molecular genetic testing in the diagnosis of sporadic cases of Huntington's chorea]. / Molekuliarno-geneticheskoe testirovanie v diagnostike sporadicheskikh sluchaev khorei Gentingtona.

Huntington's disease is characterized by autosomal dominant transmission and a complete penetrance of the mutant gene. Mutation in Huntington's disease consists in expansion of the unstable tandem CAG-trinucleotide repeats. This discovery allowed to perform a precise DNA diagnosis of the mutant gene carriers. Direct DNA diagnosis has a special importance in sporadic cases of the disease. We performed direct DNA diagnosis in 4 patients with sporadic choreic hyperkinesis, and elaborated a modified protocol for DNA amplification. The obtained results are discussed from the viewpoint of current knowledge about the nature of the Huntington's disease gene.

[Presymptomatic DNA diagnosis of spinocerebellar ataxia type 1]. / Presimptomnaia DNK-diagnostika spinotserebelliarnoi ataksii 1-go tipa.

Hereditary autosomal dominant ataxias is a clinically and genetically heterogeneous group of diseases characterized by a progressive ataxia combined with the signs of multisystem involvement of the brain and spinal cord. The modern classification of these disorders of the central nervous system is based on recent advances in molecular genetics. In a form of dominant ataxia, spinocerebellar ataxia type 1 (SCA1), the mutation consists of an increased number of copies (expansion) of trinucleotide repeats within the causative gene. This mutational mechanism is characteristic of a group of hereditary neurodegenerative diseases. Revealing this phenomenon provided a tool for direct DNA diagnosis of SCA1 at any stage of the disease, including the preclinical one. This is the first reported case of a direct DNA diagnosis of SCA1 in Russia. The diagnosis was performed in five healthy persons from the risk group, i.e., relatives of patients with a molecularly proven SCA1. Three persons were diagnosed to be presymptomatic carriers of the mutant SCA1 gene; in two persons, the mutation was not found. A complex of moral, ethical, medical, and social problems connected with the application of direct DNA testing of SCA1 in genetic counselling is discussed.

Spinocerebellar ataxia type 1 in Russia.

Spinocerebellar ataxia type 1 (SCA1) is one form of autosomal dominant cerebellar ataxia (ADCA) caused by trinucleotide (CAG) repeat expansion within a mutant gene. We investigated 25 patients from 15 Russian ADCA families for SCA1 mutation and found an expanded CAG repeat in 5 families. Mutant chromosomes contained 41-51 CAG repeats (mean 46.1, SD 3.1), and normal chromosomes displayed 21-27 repeat units (mean 24.7, SD 1.3). Progressive cerebellar ataxia in our series of SCA1 patients was very commonly associated with dysarthria (in all cases) and pyramidal signs (in 10 of 11 cases). In three patients from one family we found optic atrophy, which has never been described before in genetically proven cases of SCA1. We observed no specific clinical features distinguishing SCA1 from non-SCA1 patients. In contrast to the high frequency of SCA1 in our series, we found no patients with Machado-Joseph disease, another form of ADCA caused by expanded CAG repeat.

[The molecular genetic approach to the study of dominant spinocerebellar ataxias]. / Molekuliarno-geneticheskii podkhod v izuchenii dominantnykh spinotserebelliarnykh ataksii.

At least 5 different genes of autosomal dominant spinocerebellar ataxias (SCA) were revealed recently. Their discovery permitted to elaborate the most perfect classification of this heterogeneous group of diseases. In two forms of ataxias (SCA1 and SCA3) the mutations consist in the expansion of CAG-trinucleotides repetitions. The Russian population of patients with dominant SCA (13 families) was examined for the first time in terms of the evaluation of mutant gene carriers of SCA1 and SCA3. SCA1 was diagnosed in 5 families on the molecular level. The cerebellar ataxia, dysarthria as well as pyramidal symptoms comprised the basis of SCA1 clinical pattern. There were no SCA3 cases at DNA-testing. The perspectives of DNA-diagnosis of inherited ataxias were considered.