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]

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 surgical results in patients with different forms of torsion dystonia]

The paper describes stereotactic operations made in 278 patients with different forms of torsion dystonia during 20 years. Late outcomes were studied and assessed in 130 patients. The duration of follow-ups was 3 to 23 years. The patients' mean age at surgery was 30.5 years. The indications for surgical treatment were ineffective medical treatment and progressive disease. Positive early and late postoperative outcomes were achieved in 93 and 70% of patients, respectively. Complications developed in 3.2 and 12.3% of patients after the first and second operations, respectively. The positive outcome depends on the form, etiology, the destructible structure or a complex of structures. Surgical treatment of patients with torsion dystonia by stereotactic operations on basal ganglia is an effective treatment that provides a steady-state positive result in 70% of patients in the late period.

De novo mutations (GAG deletion) in the DYT1 gene in two non-Jewish patients with early-onset dystonia

The DYT1 gene recently has been cloned and shown to contain a three nucleotide (GAG) deletion responsible for most cases of autosomal dominant early-onset torsion dystonia. This deletion results in the loss of one of a pair of glutamic acids in a conserved region of a novel ATP-binding protein (torsinA). Previous haplotype analysis revealed that this same deletion had arisen at least two different times in history, suggesting independent mutational events. This deletion is the only sequence change found thus far to be associated uniquely with the disease status, regardless of ethnic origin. Here we describe two patients with typical early-onset torsion dystonia of Swiss-Mennonite and non-Jewish Russian origin, respectively, that both carry this same mutation as a de novo GAG deletion. This finding proves that this 3 bp deletion in the DYT1 gene is indeed a mutation that causes early-onset torsion dystonia. The DYT1 mutation is one of the rare examples of the same recurrent mutation causing a dominantly inherited condition. The sequence surrounding the GAG deletion contains an imperfect 24 bp tandem repeat, suggesting a possible mechanism for the high frequency of this mutation.

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]

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.

[A new form of hereditary ataxia: X-linked congenital cerebellar hypoplasia (a clinical and molecular genetic analysis)]

There was performed the examination of a family with innate cerebellar hypoplasia. The disease was manifested in 7 males from 3 generations. X-linked recessive type of transmission of mutant gene was established. Clinical syndrome was characterized by delay of motor development during the first year of child's living as well as by ataxia, dysarthria, external ophthalmoplegia and nonprogressive course too. The signs of pronounced hypoplasia of hemispheres and vermis were found by means of computer and magneto-resonance investigation. Molecular genetic study (linkage-analysis) revealed that the gene of the disease was localized in proximal part of long X-chromosome's shoulder, exactly in XpII 21-q24 interval (38 centimorgan genetic distance). That was the first example of successful genetic mapping of the disease from the group of hereditary cerebellar hypoplasias.

[Mapping of the gene for autosomal-recessive progressive muscular dystrophy in an isolate from a highland region of Dagestan to chromosome 2-13]

A unique inbred Avar family from an isolate of the Dagestan highland was studied. Unusual phenotypic expression of autosomal recessive progressive muscular dystrophy was revealed in 12 members of this family from three generations. Limb-girdle (proximal) muscular dystrophy (LGMD) was detected in nine patients, while the other three patients displayed typical distal myopathy (DM). Genetic linkage analysis with several candidate loci determining various forms of muscular dystrophy allowed a gene for this polymorphic syndrome to be assigned to chromosome 2p13. In spite of the difference in clinical manifestation, all patients appeared to be homozygous for a unique haplotype. This implies the founder effect and proves the same genetic basis of LGMD and DM in the family. Recombination analysis showed that the centromeric and telomeric ends of the gene region are marked with D2S2111 and D2S327, respectively (genetic distance < 1 cM). This region is overlapped by two larger regions in which the genes for LGMD type 2B (LGMD2B) and Miyoshi myopathy were recently mapped. Complex analysis of clinical and genetic data indicated that LGMD2B, Miyoshi myopathy, and the revealed polymorphic syndrome may represent allelic variants of 2p13-linked autosomal recessive muscular dystrophy.

Refined genetic location of the chromosome 2p-linked progressive muscular dystrophy gene

Autosomal recessive progressive muscular dystrophies may be clinically subclassified into limb-girdle muscular dystrophy (LGMD) and distal myopathy (DM), each clinical form being genetically heterogeneous. Genes for LGMD type 2B and Miyoshi myopathy (a form of DM) have been mapped to essentially the same region on chromosome 2p. We described recently a large inbred family with autosomal recessive muscular dystrophy in which the LGMD and the DM phenotypes were manifested in separate affected members, and we assigned the gene for this condition to the same locus as in LGMD2B and Miyoshi myopathy. Here we report extended haplotypes in this family generated from 15 markers located at the region of interest on chromosome 2p13. Key recombinants allowed us to reduce further the candidate region for this polymorphic condition and defined the loci D2S327 and D2S2111 as the most likely boundaries of the mutant gene.

[Presymptomatic DNA diagnosis of spinocerebellar ataxia type 1]

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.

Fine localization of the torsion dystonia gene (DYT1) on human chromosome 9q34: YAC map and linkage disequilibrium

The DYT1 gene, which maps to chromosome 9q34, appears to be responsible for most cases of early-onset torsion dystonia in both Ashkenazic Jewish (AJ) and non-Jewish families. This disease is inherited in an autosomal dominant mode with reduced penetrance (30%-40%). The abnormal involuntary movements associated with this disease are believed to be caused by unbalanced neural transmission in the basal ganglia. Previous linkage disequilibrium studies in the AJ population placed the DYT1 gene in a 2-cM region between the loci D9S62a and ASS. A YAC contig has now been created spanning 600 kb of this region including D9S62a. The location of the DYT1 gene has been refined within this contig using several new polymorphic loci to expand the linkage disequilibrium analysis of the AJ founder mutation. The most likely location of the DYT1 gene is within a 150 kb region between the loci D9S2161 and D9S63.

[Immunochemical correlates of the severity of Parkinson's disease]

The serum samples from 29 patients with Parkinson's disease were analysed for the levels of the autoantibodies (a-AB) and antiidiotype antibodies (AIAB) to the proteins of nervous system S-100, GFAP, NKP and MP-65. High levels of a-AB or AIAB to at least 3 proteins were seen in patients with severe course of the disease. No significant changes of these levels were observed in patients with light course of the disease. The plasmapheresis was carried out to some patients with severe course of the disease. After this procedure the decrease of neurological deficit from number 21 +/- 2 to 8 +/- 1 on Webster's scale and decrease of a-AB and AIAB levels to normal values (in some cases it became lower than normal values) were observed. It can be concluded that the levels of the a-AB to the nervous tissue proteins correlate with clinical condition of the patient.

Clinical and molecular analysis of a large family with three distinct phenotypes of progressive muscular dystrophy

We describe a unique six-generation, highly consanguineous family originating from an isolated mountainous village in the Russian province of Daghestan. Three separate clinical phenotypes of progressive muscular dystrophy were identified in this large family. Seven patients developed a classical limb-girdle variant of muscular dystrophy (LGMD), with disease onset at 15-30 years and loss of ambulation within a 25-year course. The second group included three patients with a slowly progressive distal myopathy first manifested in the late teens and confined to the tibial and calf muscles. Each of these two phenotypes segregated independently as an autosomal recessive trait, and muscle biopsies showed non-specific myopathic changes. Lastly, two male siblings exhibited an atypical variant of Duchenne muscular dystrophy confirmed by detection of a deletion in the dystrophin gene. To clarify the molecular basis of the polymorphic autosomal recessive form of muscular dystrophy in this kindred, we performed molecular genetic studies on 67 family members and obtained significant evidence for linkage to chromosome 2p. A maximum pairwise lod (logarithm of odds) score of 5.64 was achieved at the zero recombination fraction (i.e. at theta = 0.00) for locus D2S291; multipoint linkage analysis confirmed the most likely location of a mutant gene near D2S291. The patients with LGMD and those with the distal muscular dystrophy phenotype share a common affected homozygous haplotype associated with the same founder chromosome; key recombinants defined D2S286 and D2S292 to be the closest loci flanking the mutant gene. Remarkably, two clinically distinct forms of autosomal recessive muscular dystrophy, LGMD type 2B (LGMD2B) and Miyoshi myopathy, were recently mapped to the same locus. We suggest that all three chromosome 2p-linked conditions may represent allelic disorders, i.e. different phenotypic expressions of a single gene.

[Search for expansion of CAG-repeats in DNA sequences expressed in the brain of humans with psychiatric and neurological diseases]

Dynamic mutations due to trinucleotide repeat expansion are a new class of human genome mutations. CAG repeat expansion in the coding region of associated genes is the molecular genetic basis of the several diseases of nervous system. Eight DNA sequences with CAG repeats expressed in human brain were chosen from the GenBank database. The search of CAG expansion was carried out for patients with schizophrenia (brain and blood) and essential tremor. CAG repeat expansion has not been found for the loci. The distribution of allelic sizes is similar in the patients and control samples. Locus HS0073 has shown the polymorphism of the length for CAG repeat alleles. Statistically reliable excess of the homozygotes has been found for schizophrenic patients.

X-linked nonprogressive congenital cerebellar hypoplasia: clinical description and mapping to chromosome Xq

We examined a large family in which an X-linked recessive congenital ataxia manifested in 7 males from three generations. The affected boys first exhibited a marked delay of early developmental motor milestones. A neurological syndrome became evident by 5 to 7 years of age and included cerebellar ataxia, dysarthria, and external ophthalmoplegia; there were no symptoms of mental retardation, spastic paraparesis, or sensory loss. Neuroimaging studies revealed hypoplasia of cerebellar hemispheres and vermis. The disease showed no progression beyond early childhood. The unique heredity and clinical features clearly distinguish this new entity from a variety of previously described familial ataxias. Pairwise linkage analysis and haplotype reconstruction allowed us to map the gene responsible for this disorder to a 38-cM interval on chromosome Xp11.21-q24 flanked by the loci DXS991 and DXS1001. Upon multipoint linkage analysis, the disease gene was determined to be located most likely in the proximal part of chromosome Xq, with the maximal lod score of 4.66 at the locus DXS1059 (Xq23). This is the first example of the genetic mapping of a pure congenital cerebellar hypoplasia syndrome.

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.

[Genetic study of idiopathic torsion dystonia in Russia]

Inheritance of idiopathic torsion dystonia (ITD) was studied in 41 Russian families including 41 probands with generalized, focal, and segmental dystonia and 140 recurred cases. Affected relatives appeared in two or more generations in 31 families analyzed. It was shown that in 76% of segregated cases, ITD was inherited as an autosomal dominant trait with a penetrance of 40% and varying expression. An autosomal recessive type was observed in 24% of the cases. Approximately 10% of the cases of disease could be caused by a new mutation and 14.6% by a nongenetic phenotype similar to genetic forms in its clinical symptoms. ITD with the X-linked recessive type of inheritance did not occur in the families studied. The recurrence risk was 20% in autosomal dominant forms. The risk correlated with age the relative's: clinical symptoms developed in 98.4% of patients by the age of 30.

[Analysis of trinucleotide repeat expansion as a new mechanism of mutation in Huntington's chorea: theoretical and applied aspects]

The Huntington's chorea mutation consists of expansion of trinucleotide CAG repeats in the recently discovered gene IT-15. In this work, for the first time in a population of Russian patients, correlations between the number of copies of CAG repeats and various clinical characteristics of the disease are investigated. It is established that the degree of triplet expansion determines the age of onset of the disease and the rate of progression of the neurological and mental symptoms of Huntington's chorea, and it is also shown that the genetic instability of the mutant allele is considerably higher upon transmission of the disease gene along the paternal line. We obtained direct confirmation of the possibility of genetic instability of a normal allele inherited paternally. In this work, the first successful direct (including preclinical) DNA diagnosis in Russia of Huntington's chorea was obtained.

[A new mechanism of mutation in man: expansion of trinucleotide repeats]

An analysis of a novel, recently discovered class of mutations in man - an expansion, i.e., an increase of the copy number of intragenic unstable trinucleotide repeats - is presented. The expansion of trinucleotide repeats causes the development of at least seven hereditary diseases which damage the nervous system: the fragile X chromosome syndrome (two separate variants of the disease - FRAXA and FRAXE), myotonic dystrophy, spinal and bulbar Kennedy's amyotrophy, Huntington's chorea, type 1 spinocerebellar ataxia, and dentatorubral-pallidolyusian atrophy. The discovery of triplet expansion allows a satisfactory explanation on the molecular level of a series of unusual clinical genetic phenomena, such as anticipation, the ¿paternal transmission¿ effect, the ¿Sherman paradox¿, and others. The common properties and the distinctions of unstable trinucleotide mutations in the above-mentioned nosologic forms are analyzed comprehensively among for the mechanism by which these mutations cause disease, the time of their appearance in ontogenesis, and various clinical genetic correlations. The evolutionary origin of this class of mutations and, in particular, the role of alleles with an ¿intermediate¿ triplet number, which are the persistent reservoir of mutations arising de novo in a population, are also discussed. The possible implication of unstable trinucleotide repeats for a series of other hereditary diseases, such as spinocerebellar ataxia of type 2, Machado-Joseph disease, hereditary spastic paraplegia, essential tremor, schizophrenia and others, is also suggested.

Trinucleotide repeat length and rate of progression of Huntington's disease

The Huntington's disease gene contains an expanded unstable (CAG)n repeat, and the repeat lengths have been shown to correlate with the age of onset. Using detailed clinical scales, we evaluated the rate of progression of Huntington's disease and its relationship to the number of triplet repeats. We found significant positive correlation between the rate of progression of clinical symptoms (both neurological and psychiatric) and CAG repeat length. These data suggest an important role of expanded trinucleotide repeat length in affecting the pathological process during the entire course of Huntington's disease.

[Comparative study of human erythrocyte membranes in normal people and in Huntington's chorea patients]

Erythrocytes of healthy volunteers and of patients with hereditary chorea were studied. Evaluation of the state of cellular membrane was carried out by measuring osmotic resistance, activity of Na+, K(+)-ATPase and protein composition. In the patients osmotic resistance of erythrocytes was distinctly decreased down to 66.3 +/- 3.3, while the Na+, K(+)-ATPase activity was increased 4-fold as compared with controls. Protein composition of erythrocyte membranes, studied by means of two-dimensional electrophoresis, was similar both in healthy persons and in patients with hereditary chorea when the electrophoretograms were analyzed visually. An additional protein with Mr = 30,000 and r-1-0.25 was detected in one of the patients. Slowly sedimenting fraction of erythrocytes was found in almost all the patients with hereditary chorea when erythrocytes aging was studied by means of fractionation in Ficoll density gradient. The fraction was not observed in healthy persons. These data suggest that the cell membranes in Huntington's chorea are altered as compared with normal state.

[Protective effect rendered by human ceruloplasmin on erythrocytes in hepatocerebral dystrophy]

In order to elucidate the protective effect of human ceruloplasmin (CP) on erythrocytes in patients with hepatocerebral dystrophy (HCD), the parameters reflecting the interaction of CP from the blood of healthy donors (n-CP) and of HCD patients (h-CP) with erythrocytes from healthy donors (n-ER) and from HCD patients (h-ER) were estimated. The protective effects of n-CP and h-CP on n-ER and h-ER during the Cu2+-induced lysis were compared. It was shown that the ability of h-CP to prevent the human ER breakdown upon Cu2+-induced lysis is much lower (approximately 3-fold) than that of n-CP. The differences in the protective effect of n-CP and h-CP are manifested in a greater degree during the n-ER lysis than during the h-ER lysis.