Progressive myoclonus epilepsy and mitochondrial myopathy associated with mutations in the tRNAser(UCN) gene

We report seven unrelated families with mitochondrial tRNA^Ser(UCN) gene mutations at three different loci. A novel G7497A mutation is found in two families, both of which present with progressive myopathy, ragged-red fibers, lactic acidosis, and deficiency of repiratory chain complexes I and IV. This mutation presumably affects the tertiary tRNA^Ser(UCN) dihydrouridine interaction. Mutations 7472 insC and T7512C, found in three and two families, respectively, are associated with myoclonus epilepsy, deafness, ataxia, cognitive impairment, and complex IV deficiency. No ragged-red fibers or ultrastructural abnormalities are seen. It is interesting that 6 of our 7 index patients are apparently homoplasmic, indicating a minor pathogenetic power of the tRNA^Ser(UCN) mutations.     

Screening for mutations in Spanish families with myotonia. Functional analysis of novel mutations in CLCN1 gene

Myotonia congenita is an inherited muscle disorder caused by mutations in the CLCN1 gene, a voltage-gated chloride channel of skeletal muscle. We have studied 48 families with myotonia, 32 out of them carrying mutations in CLCN1 gene and eight carry mutations in SCN4A gene. We have found 26 different mutations in CLCN1 gene, including 13 not reported previously. Among those 26 mutations, c.180+3A>T in intron 1 is present in nearly one half of the Spanish families in this series, the largest one analyzed in Spain so far. Although scarce data have been published on the frequency of mutation c.180+3A>T in other populations, our data suggest that this mutation is more frequent in Spain than in other European populations. In addition, expression in HEK293 cells of the new missense mutants Tyr137Asp, Gly230Val, Gly233Val, Tyr302His, Gly416Glu, Arg421Cys, Asn567Lys and Gln788Pro, demonstrated that these DNA variants are disease-causing mutations that abrogate chloride currents.     

Novel mutations in the arylsulfatase A gene in eight Italian families with metachromatic leukodystrophy.

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by arylsulfatase A (ARSA) deficiency. We analysed the ARSA gene in eight unrelated Italian families with different clinical variants of MLD and identified three novel mutations: two Ser406Gly, (Glu329Ter) associated with late infantile MLD and one (Leu52Pro) with juvenile MLD. Only one family carried a pseudodeficiency allele (Asn350Ser). The IVS2+1G>A mutation occurred in four families. We also identified three polymorphisms, all in heterozygosis: Thr391Ser was present in five families, Trp193Cys in four families, and Ala210Ala in one family. We could identify 100% of the alleles causing MLD in the families, involving 12 different mutations, resulting in improved prognosis and genetic counselling.     

Molecular and structural analysis of metachromatic leukodystrophy patients in Indian population

Metachromatic leukodystrophy (MLD) is an autosomal recessive disorder caused by mutations in arylsulfatase A (ARSA) gene. No work on molecular genetics of MLD has been reported from India and the mutational spectrum in Indian patients is not known. The present study was undertaken to identify mutations in arylsulfatase A gene in Indian MLD patients, to evaluate genotype-phenotype correlation, and to see the effect of the novel mutants on the protein. Twenty MLD patients (16 families) were screened by ARMS PCR for the most common mutation (c.459+1G>A). Pseudodeficiency alleles were tested by RFLP method whereas rare and novel mutations were scanned by Conformation Sensitive Gel Electrophoresis (CSGE), followed by sequencing. The genotype-phenotype correlation was also attempted. Protein homology modeling analysis was carried out for two novel missense mutations identified, to assess the effect of these mutations on the protein conformation. Nine pathogenic alleles were found in 13 patients (65%). Four previously reported mutations and five novel variants were identified. Five patients (35%) were found to have pseudodeficiency alleles, c.1049A>G (p.Asn350Ser) and c.1524+95A>G. Genotype-phenotype correlation was found to be difficult to establish. Protein modeling studies showed that the mutations cause loss of interactions leading to conformational change in ASA protein. The study identified the mutational spectrum of Indian MLD patients, which will be helpful in genetic counseling, carrier detection and establishing prenatal diagnosis. Homology modeling helped to study conformational change in protein and has implications in generating novel therapeutic molecules.     

A founder mutation in French-Canadian families with X-linked hereditary neuropathy

BACKGROUND: The aim of the present study was to identify the mutations in the connexin 32 gene in French-Canadian families with X-linked Charcot-Marie-Tooth disease (CMTX). METHODS: Molecular analysis was performed by nonisotopic single strand conformation polymorphism (SSCP) analysis and sequencing. Clinical evaluation was carried out according to the scale defined by the European Hereditary Motor and Sensory Neuropathy Consortium. RESULTS: In one family, the mutation Arg142Trp was located in the transmembrane domain III whereas, in four other families we identified a novel mutation (Ser26Trp) located in the transmembrane domain I of the connexin 32 gene. Haplotype analysis revealed that these four families are related and suggests a founder mutation. Sixteen patients from these four families were studied. As expected, all the affected males were more clinically affected than the females and all affected patients exhibited some electrophysiological characteristics of demyelination. CONCLUSION: Our study suggests that the Ser26Trp mutation may cause a primary demyelinating neuropathy that is not associated with a specific clinical phenotype. We also find evidence that the majority of kindreds share a common ancestor.     

Novel NTRK1 mutations cause hereditary sensory and autonomic neuropathy type IV: demonstration of a founder mutation in the Turkish population

Hereditary sensory and autonomic neuropathy type IV (HSAN IV), or congenital insensitivity to pain with anhidrosis, is an autosomal recessive disorder characterized by insensitivity to noxious stimuli, anhidrosis from deinnervated sweat glands, and delayed mental and motor development. Mutations in the neurotrophic tyrosine kinase receptor type 1 (NTRK1), a receptor in the neurotrophin signaling pathway phosphorylated in response to nerve growth factor, are associated with this disorder. We identified six families from Northern Central Turkey with HSAN IV. We screened the NTRK1 gene for mutations in these families. Microsatellite and single nucleotide polymorphism (SNP) markers on the Affymetrix 250K chip platform were used to determine the haplotypes for three families harboring the same mutation. Screening for mutations in the NTRK1 gene demonstrated one novel frameshift mutation, two novel nonsense mutations, and three unrelated kindreds with the same splice-site mutation. Genotyping of the three families with the identical splice-site mutation revealed that they share the same haplotype. This report broadens the spectrum of mutations in NTRK1 that cause HSAN IV and demonstrates a founder mutation in the Turkish population. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Beyhan Tüysüz and Fatih Bayrakli contributed equally to this work.     

Oculopharyngeal MD among Bukhara Jews is due to a founder (GCG)9 mutation in the PABP2 gene

OBJECTIVE: To determine whether all cases of oculopharyngeal muscular dystrophy (OPMD) among Bukhara Jews share the same founder mutation. BACKGROUND: Autosomal dominant OPMD is caused by a (GCG)8-13 repeat expansion in the polyadenylation binding protein 2 (PABP2) gene. The disease has a worldwide distribution but is particularly prevalent in Bukhara Jews and in French Canadians, in whom it was introduced by three sisters in 1648. METHODS: We established the size of the PABP2 mutation in 23 Bukhara Jewish patients belonging to eight unrelated families. In all families, we constructed haplotypes for the carrying chromosomes composed of the alleles for eight chromosome 14q polymorphic markers. RESULTS: All patients share a (GCG)9 PABP2 mutation and a four-marker haplotype. Furthermore, a shared intron single nucleotide polymorphism (SNP) in the PABP2 gene 2.6Kb from the mutation was not observed in 22 families with (GCG)9 mutations from nine different countries. The smaller size of the chromosomal region in linkage disequilibrium around the mutation in Bukhara Jews, as compared with French Canadians, suggests a founder effect that occurred more than 350 years ago. Based on the Luria-Delbrück corrected "genetic clock," we estimate that the mutation appeared or was introduced once in the Bukhara Jewish population between AD 872 and 1512 (mean, AD 1243). CONCLUSION: OPMD among Bukhara Jews is the result of a shared, historically distinct, PABP2 (GCG)9 mutation that likely arose or was introduced in this population at the time they first settled in Bukhara and Samarkand during the 13th or 14th centuries.     

Mutation analysis in myophosphorylase deficiency (McArdle's disease)

Inherited deficiency of myophosphorylase leads to glycogen storage disease type V (McArdle's disease). We performed mutation analysis in 9 patients of eight unrelated families from Germany with typical cliniclal presentation of myophos-phorylase deficiency. Beside previously described mutations we identified four novel mutations in the myophorsphorylase gene. Four patients were homozygous for a nonsense mutation Arg49Stop that has been reported to be the most common mutation in white patients. Two affected siblings were compound heterozygotes for a novel missense mutation Gly685Arg and the nonsense mutation Arg49Stop. One patient carried a novel nonsense mutation Arg575Stop and a previously identified missense mutation Gly204Ser. In another patient, we identified a novel missense mutation Gln665Glu and a single-base deletion delA in Lys753. One patient of Turkish ancestry carried a newly identified homozygous A-to-G transition (ATG to GTG) abolishing the translation initiation codon of the myophosphorylase gene. These results suggest that Arg49Stop also is the most common genetic error associated with myophosphorylase deficiency in the German population. Our findings further demonstrate molecular heterogeneity of myophosphorylase deficiency among the clinically homogenous patients we studied.     

Mutations in phenotypically mild D-2-hydroxyglutaric aciduria

D-2-hydroxyglutaric aciduria is a neurometabolic disorder with mild and severe phenotypes. Recently, we reported pathogenic mutations in the D-2-hydroxyglutarate dehydrogenase gene as the cause of the severe phenotype of D-2-hydroxyglutaric aciduria in two patients. Here, we report two novel pathogenic mutations in this gene in one patient with a mild presentation and two asymptomatic siblings with D-2-hydroxyglutaric aciduria from two unrelated consanguineous Palestinian families: a splice error (IVS4-2A-->G) and a missense mutation (c.1315A-->G;p.Asn439Asp). Overexpression of this mutant protein showed marked reduction of the enzyme activity.     

Creutzfeldt-Jakob disease cosegregates with the codon 178Asn PRNP mutation in families of European origin.

We recently discovered an amino acid-altering heterozygous mutation in codon 178 of the PRNP amyloid precursor gene in patients with familial Creutzfeldt-Jakob disease. This mutation is now shown to be associated with the occurrence of disease in 7 unrelated families of Western European origin, among which a total of 65 members are known to have died from Creutzfeldt-Jakob disease. The mutation was detected in each of 17 tested patients, including at least 1 affected member of each family, and in 16 of 36 of their first-degree relatives, but not in affected families with other mutations, patients with the nonfamilial form of the disease, or 83 healthy control individuals. Linkage analysis in two informative families yielded a lod score of 5.30, which, because no recombinants were found, strongly suggests that codon 178Asn is the actual disease mutation.     

SPG4 founder effect in French Canadians with hereditary spastic paraplegia

BACKGROUND: The most common cause of autosomal dominant Hereditary Spastic Paraplegia (HSP) is mutations in the SPG4 gene. We have previously identified novel SPG4 mutations in a collection of North American families including the c.G1801A mutation present in two families from Quebec. The aim of this study is to estimate the frequency of the c.G1801A mutation in the French Canadian (FC) population and to determine whether this mutation originates from a common ancestor. METHODS: We collected and sequenced exon 15 in probands of 37 families. Genotypes of markers flanking the SPG4 gene were used to construct haplotypes in five families. Clinical information was reviewed by a neurologist with expertise in HSP. RESULTS: We have identified three additional unrelated families with the c.G1801A mutation and haplotype analysis revealed that all five families share a common ancestor. The mutation is present in 7% of all our FC families and explains half of our spastin linked FC families. The phenotype associated with the c.G1801A genotype is pure HSP with bladder involvement. CONCLUSION: In this study we have determined that the relative frequency of the c.G1801A mutation in our FC collection is 7%, and approximately 50% in the spastin positive FC group. This mutation is the most common HSP mutation identified in this population to date and is suggestive of a founder effect in Quebec.     

Clinicogenetic study of mutations in LRRK2 exon 41 in Parkinson's disease patients from 18 countries.

We screened LRRK2 mutations in exon 41 in 904 parkin-negative Parkinson's disease (PD) patients (868 probands) from 18 countries across 5 continents. We found three heterozygous missense (novel I2012T, G2019S, and I2020T) mutations in LRRK2 exon 41. We identified 11 (1.3%) among 868 PD probands, including 2 sporadic cases and 8 (6.2%) of 130 autosomal dominant PD families. The LRRK2 mutations in exon 41 exhibited relatively common and worldwide distribution. Among the three mutations in exon 41, it has been reported that Caucasian patients with G2019S mutation have a single-founder effect. In the present study, Japanese patients with G2019S were unlikely to have a single founder from the Caucasian patients. In contrast, I2020T mutation has a single-founder effect in Japanese patients. Clinically, patients with LRRK2 mutations had typical idiopathic PD. Notably, several patients developed dementia and psychosis, and one with I2020T had low cardiac (123)I-metaiodobenzylguanidine (MIBG) heart/mediastinum ratio, although the ratio was not low in other patients with I2020T or G2019S. Clinical phenotypes including psychosis, dementia, and MIBG ratios are also heterogeneous, similar to neuropathology, in PD associated with LRRK2 mutations.     

Founder effect and ancestral origin of the spinocerebellar ataxia type 7 (SCA7) mutation in Mexican families

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant disease characterized by progressive cerebellar ataxia and macular degeneration causing progressive blindness. It accounts for 1 to 11.6 % of spinocerebellar ataxias (SCAs) cases worldwide and for 7.4 % of SCA7 cases in Mexico. We identified a cluster of SCA7 families who resided in a circumscribed area of Veracruz and investigated whether the high incidence of the disease in this region was due to a founder effect. A total of 181 individuals from 20 families were studied. Four microsatellite markers and one SNP flanking the ATNX7 gene were genotyped and the ancestral origin and local ancestry analysis of the SCA7 mutation were evaluated. Ninety individuals from 19 families had the SCA7 mutation; all were found to share a common haplotype, suggesting that the mutation in these families originated from a common ancestor. Ancestral origin and local ancestry analysis of SCA7 showed that the chromosomal segment containing the mutation was of European origin. We here present evidence strongly suggesting that the high frequency of SCA7 in Veracruz is due to a founder effect and that the mutation is most likely of European origin with greatest resemblance to the Finnish population.     

Recurrent myoglobinuria in a sporadic patient with a novel mitochondrial DNA tRNA(Ile) mutation

The differential diagnosis of myoglobinuria includes multiple etiologies, such as infection, inflammation, trauma, endocrinopathies, drugs toxicity, and primary metabolic disorders. Metabolic myopathies can be due to inherited disorders of glycogen metabolism or to defects of fatty acid oxidation. Primary respiratory chain dysfunction is a rare cause of myoglobinuria, but it has been described in sporadic cases with mutations in genes encoding cytochrome b or cytochrome c oxidase (COX) subunits and in four cases with tRNA mutations. We describe a 39-year-old woman with myalgia and exercise-related recurrent myoglobinuria, who harbored a novel mitochondrial DNA mutation at nucleotide 4281 (m.4281A>G) in the tRNA-isoleucine gene. Her muscle biopsy revealed ragged-red and COX-deficient fibers. No deletions or duplication were detected by Southern blot analysis. The m.4281A>G mutation was present in the patient's muscle with a mutation load of 46% and was detected in trace amounts in urine and cheek mucosa. Single-fiber analysis revealed significantly higher levels of the mutation in COX-deficient (65%) than in normal fibers (45%). This novel mutation has to be added to the molecular causes of recurrent myoglobinuria.     

Independent occurrence of the CHRNA4 Ser248Phe mutation in a Norwegian family with nocturnal frontal lobe epilepsy

PURPOSE: To describe the clinical features of a family from Northern Norway in which autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is associated with a Ser248Phe amino acid exchange in the second transmembrane domain of the neuronal nicotinic acetylcholine receptor alpha4 subunit (CHRNA4). We also tested for evidence of a de novo mutation or founder effect by comparing haplotypes with the original Australian family where the Ser248Phe mutation was first described. METHODS: Clinical details were obtained from 19 family members. Personal interviews and genetic analysis were carried out in 17. Parts of the coding region of CHRNA4 were sequenced, and two known polymorphisms (bp555/FokI, bp594/CfoI) were typed by restriction analysis. RESULTS: Eleven individuals had ADNFLE. The haplotypes of the mutation-carrying alleles of affected individuals from the Northern Norwegian and the Australian ADNFLE family are different. The phenotypic expressions are remarkably similar. CONCLUSIONS: The Ser248Phe mutation occurred independently in both families. Given the rarity of the disease, this suggests that not only the position of a mutation in the coding sequence but also the type of an amino acid exchange is important for the etiology of ADNFLE. The phenotypic similarity of these two families with different genetic backgrounds suggests that the Ser248Phe mutation largely determines the phenotype, with relatively little influence of other background genes.     

Mutation analysis of oculopharyngeal muscular dystrophy in Hispanic American families.

BACKGROUND: Oculopharyngeal muscular dystrophy (OPMD) is a late-onset autosomal dominant muscular dystrophy characterized by progressive ptosis, swallowing difficulties, and proximal limb weakness. Recently, the genetic basis of this disease has been characterized by mutations in the PABP2 gene that involve short expansions of the trinucleotide repeat GCG. OBJECTIVES: To independently confirm the presence and study the meiotic stability of the GCG expansion mutations in a distinct ethnic population with OPMD. SETTINGS: Hospital and university research laboratories in Los Angeles, Calif. SUBJECTS AND METHODS: Three unrelated families of Hispanic American descent were identified in whom OPMD was transmitted in an autosomal dominant pattern. All of these families can trace affected ancestors to the southwestern United States or to the bordering states of Mexico. In these families, 14 persons with OPMD were identified and studied. RESULTS: Our results confirm that in these families, expansion mutations characterized by a gain of 3 GCG repeats in the wild-type allele result in an abnormal nucleotide length of 9 GCG repeats in the PABP2 gene. In these families, these mutations are associated with the OPMD phenotype. The identical repeat mutation ([GCG]9) is found in all affected members of these unrelated families and shows relative meiotic stability. CONCLUSIONS: These results support and extend our study of haplotype analysis and suggest that a founder effect may have occurred for OPMD in this Hispanic American population.     

Molecular heterogeneity of myophosphorylase deficiency (McArdle's disease): a genotype-phenotype correlation study.

We report on 54 Spanish patients with McArdle's disease from 40 unrelated families. Molecular analysis revealed that the most common R49X mutation was present in 70% of patients and 55% of alleles. The G204S mutation was less frequent and found in 14.8% of patients and 9% of mutant alleles. The W797R mutation was observed in 16.5% of patients, accounting for 13.7% of mutant alleles. Moreover, 78% of mutant alleles among Spanish patients can be identified by using polymerase chain reaction-restriction fragment length polymorphism analysis for the R49X, G204S, and W797R mutations, which makes noninvasive diagnosis possible through molecular genetic analysis of blood DNA. Six novel mutations were found. Three were missense mutations, E348K, R601W, and A703V; two nonsense mutations, E124X and Q754X; and one single base pair deletion, 533 delA. No clear genotype-phenotype correlation emerges from our study. Most of the mutations of uncharged and solvent inaccessible residues and the truncations must disrupt the basic structure of the protein. The mutations of charged residues would be expected to interfere with internal hydrogen bonding networks, introducing severe incompatible partnering that is caused by poor packing or electrostatic repulsions.     

Hereditary spastic paraplegia: clinical genetic study of 15 families

BACKGROUND: Autosomal dominant hereditary spastic paraplegia (ADHSP) is mainly caused by mutations in the SPG4 gene, which encodes a new member of the AAA (adenosine triphosphatases associated with diverse cellular activities) protein family (spastin). Accumulation of genotype-phenotype correlation is important for better understanding of SPG4-linked hereditary spastic paraplegia. OBJECTIVES: To perform a clinical and genetic study of families with ADHSP and to perform the functional analysis of the founder mutation discovered in the SPG4 gene. DESIGN: Genetic and clinical study.Patients Fifteen unrelated families with ADHSP originating from southern Scotland. MAIN OUTCOME MEASURES: Clinical assessment, linkage analysis, haplotype study, expression of mutant spastin protein in cultured cells. RESULTS: Nine families with ADHSP were linked to the SPG4 locus at 2p21-p24. Sequence analysis of SPG4showed a novel N386S mutation in all 9 of these families. Expression of mutant spastin showed aberrant distribution in cultured cells. Haplotype analysis suggested the existence of a common founder. Clinical examination of the affected members carrying the mutation showed phenotypic variations including broad range of age at onset and disease duration and additional neurologic features such as mental retardation. Magnetic resonance imaging demonstrated unique features, including thin corpus callosum and atrophy of the cerebellum in 2 patients. Linkage and sequence analyses showed no evidence of linkage to the currently known ADHSP loci in the remaining 6 families. CONCLUSIONS: A founder SPG4 mutation N386S was identified in the families with ADHSP originating from southern Scotland. Clinical investigation showed intrafamilial and interfamilial phenotypic variations. The genetic study demonstrated evidence of further genetic heterogeneity in ADHSP.     

A missense mutation (Tyr88 to Cys) in the platelet membrane glycoprotein Ibbeta gene affects GPIb/IX complex expression--Bernard-Soulier syndrome in the homozygous form and giant platelets in the heterozygous form

This study examined the molecular basis of a missense mutation of the platelet glycoprotein (GP) Ibbeta gene in two families. In the propositus with a novel form of Bernard-Soulier syndrome (BSS) from Family I, only GPIbalpha was detectable in reduced amounts on platelet surfaces by flow cytometry. There were no GPIX or GPIbbeta found by immunoblotting. DNA sequencing analysis showed a homozygous mutation in the GPIbbeta gene which changed Tyr (TAC) to Cys (TGC) at residue 88. Her parents were heterozygous for Tyr88Cys in the GPIbbeta gene. In transient transfection studies on 293T cells, both Tyr88Cys and Tyr88Ala mutations suppressed the expression of GPIb/IX complexes. In addition, Tyr88Cys GPIbbeta mutation was found to exert a dominant negative effect on the GPIbalpha expression. Five individuals from Family II, four of whom reported elsewhere as having giant platelet disorders with normal aggregation (BLOOD, 1997: 89: 2404) and one newly analyzed in this study, were heterozygous for Tyr88Cys in the GPIbbeta gene. Microsatellite analysis of chromosome 22 showed a common haplotype in 8 of the individuals with Tyr88Cys mutations in Families I and II. Tyr88 in the GPIbbeta gene plays a significant role in the GPIb/IX expression; the defect causes BSS in a homozygous form and possibly giant platelets in a heterozygous form.     

Four Caucasian patients with mutations in the fukutin gene and variable clinical phenotype

Fukuyama congenital muscular dystrophy (FCMD) is frequent in Japan, due to a founder mutation of the fukutin gene (FKTN). Outside Japan, FKTN mutations have only been reported in a few patients with a wide spectrum of phenotypes from Walker–Warburg syndrome to limb-girdle muscular dystrophy (LGMD2M). We studied four new Caucasian patients from three unrelated families. All showed raised serum CK initially isolated in one case and muscular dystrophy. Immunohistochemical studies and haplotype analysis led us to search for mutations in FKTN. Two patients (two sisters) presented with congenital muscular dystrophy, mental retardation, and posterior fossa malformation including cysts, and brain atrophy at Brain MRI. The other two patients had normal intelligence and brain MRI. Sequencing of the FKTN gene identified three previously described mutations and two novel missense mutations. Outside Japan, fukutinopathies are associated with a large spectrum of phenotypes from isolated hyperCKaemia to severe CMD, showing a clear overlap with that of FKRP.