SPTLC1 is mutated in hereditary sensory neuropathy, type 1.

Hereditary sensory neuropathy type 1 (HSN1, MIM 162400; ref. 1) genetically maps to human chromosome 9q22 (refs. 2-4). We report here that the gene encoding a subunit of serine palmitoyltransferase is located within the HSN1 locus, expressed in dorsal root ganglia (DRG) and mutated in HSN1.

Linkage of recessive familial amyotrophic lateral sclerosis to chromosome 2q33-q35.

Amyotrophic lateral sclerosis (ALS) usually presents as a sporadic disorder of motor neurons. However, familial forms of ALS have been described--autosomal dominant forms (ALS1, ALS3), clinically indistinguishable from the sporadic form, and autosomal recessive forms with early onset and slower progression of symptoms (ALS2). To localize the gene for one of the autosomal recessive forms of ALS, we applied linkage analysis to a large inbred family from Tunisia. A lod score maximum of Zmax = 8.2 at theta = 0.00 was obtained with marker D2S72 located on chromosome 2q33-q35. The fine mapping of this region suggested that the ALS2 locus lies in the 8 cM segment flanked by D2S155 and D2S115.

Dysferlin, a novel skeletal muscle gene, is mutated in Miyoshi myopathy and limb girdle muscular dystrophy.

Miyoshi myopathy (MM) is an adult onset, recessive inherited distal muscular dystrophy that we have mapped to human chromosome 2p13. We recently constructed a 3-Mb P1-derived artificial chromosome (PAC) contig spanning the MM candidate region. This clarified the order of genetic markers across the MM locus, provided five new polymorphic markers within it and narrowed the locus to approximately 2 Mb. Five skeletal muscle expressed sequence tags (ESTs) map in this region. We report that one of these is located in a novel, full-length 6.9-kb muscle cDNA, and we designate the corresponding protein 'dysferlin'. We describe nine mutations in the dysferlin gene in nine families; five are predicted to prevent dysferlin expression. Identical mutations in the dysferlin gene can produce more than one myopathy phenotype (MM, limb girdle dystrophy, distal myopathy with anterior tibial onset).

Confirmation of linkage of type 1 hereditary sensory neuropathy to human chromosome 9q22.

OBJECTIVES: 1) To confirm linkage of hereditary sensory neuropathy type 1 (HSN-I) to human chromosome 9q22 in a large American family of German origin. 2) To construct a yeast artificial chromosome (YAC) contig spanning the HSN-I candidate interval. 3) To investigate the HSN-I contig for potential candidate genes. BACKGROUND: HSN-I is a rare peripheral neuropathy characterized by loss of temperature sensation, ulceration and osteomyelitis of the digits, and subtle distal weakness. A gene for HSN-I has previously been mapped to human chromosome 9q22.1-q22.3 between markers D9S318 and D9S176 in an 8-cM interval in four Australian families. METHODS: In a large German-American family with HSN-I, genome-wide linkage analysis was performed on 68 family members extending over five generations and including 17 affected members. Genotyping was performed with PCR, and the resulting genotypes were analyzed with two-point linkage analysis with Fastlink. A YAC contig was constructed based on the Whitehead Institute YAC contig WC9.3. RESULTS: Two-point linkage analysis resulted in a maximum lod score of 8.2 at theta = 0 for marker D9S1815. Haplotype analysis locates the HSN-I gene between markers D9S1797 and D9S197. Using YAC clones from the Centre d'Etude du Polymorphism Humain YAC Library, we constructed a YAC contig spanning these markers. Based on the radiation hybrid map of the human genome, we estimate that the size of this interval is less than 2,500 kb. CONCLUSIONS: Our study confirms linkage of a putative HSN-I gene to chromosome 9q22, considerably narrows the HSN-I locus, and provides a basis for identification of the HSN-I gene.

Linkage of Miyoshi myopathy (distal autosomal recessive muscular dystrophy) locus to chromosome 2p12-14.

Miyoshi myopathy (MM) is a young-adult-onset, autosomal recessive distal muscular dystrophy initially affecting the plantar flexors. We analyzed 12 MM families, five with consanguineous marriage, for chromosomal linkage using polymorphic microsatellite DNA markers to map the MM gene. A significant lod score was obtained with the 2p12-14 locus D2S291 (Zmax = 15.3 at theta = 0). Two additional 2p12-14 markers, D2S286 (Z = 10.7 at theta = 0) and D2S292 (Z = 7.2 at theta = 0.05), also gave significant lod scores. These markers will be useful for diagnosis of symptomatic and presymptomatic patients, prenatal and carrier diagnosis of family members carrying MM, and ultimately identification of a gene responsible for MM.

Expression of myosin isoforms and of desmin, vimentin and titin in Tunisian Duchenne-like autosomal recessive muscular dystrophy.

Morphological, morphometrical, histoenzymological, immunocytochemical and biochemical analysis were performed on muscle biopsies taken from patients suffering from tunisian autosomal recessive Duchenne-like muscular dystrophy (TDLMD) selected both by Duchenne-like clinical criteria and by the presence of normal dystrophin. Data were compared to that obtained from DMD biopsies characterized by the absence of dystrophin. The distribution of myosin heavy chain isoforms, desmin, vimentin and titin were determined in type I and type II muscle fibers. The protein pattern appeared to be less affected in TDLMD than in DMD biopsies. The regenerating fibers were mainly but not exclusively type IIC; a noticeable percentage of both type I and type II fibers coexpressed fast and slow MHC isoforms in TDLMD. This percentage was lower than in DMD. The expression of embryonic, fetal, and fast/slow myosin isoforms in type IIC fibers in TDLMD and DMD suggest different fiber type transformations in these two diseases.

Modification in the expression and localization of contractile and cytoskeletal proteins in Schwartz-Jampel syndrome.

Muscle biopsies taken from 4 patients with clinical diagnosis of Schwartz-Jampel syndrome were analyzed by enzyme-histochemical immunocytochemical and biochemical techniques. In situ distribution of the different myosin heavy chain (MHC) isoforms together with that of the cytoskeletal proteins vimentin, desmin and titin was determined in type I, type IIA, type IIB and type IIC fibers. The same muscle biopsies were analyzed for their content in myosin light chains (MLC) by two-dimensional gel electrophoresis and native myosin isoforms by pyrophosphate gel electrophoresis. The opportunity to study 4 patients of different ages, all members of the same family, permitted us to reveal several interesting features in this rare and so far poorly understood muscle pathology. (i) We observed a predominance of slow (type I) fibers in the oldest patient. (ii) Two classes of small clusters of atrophic type IIC fibers were observed. The first class corresponded to fibers which coexpressed embryonic, fetal and fast, but not slow, MHC isoforms. The fibers also displayed an abnormal distribution of desmin, vimentin and titin. The second class was composed by fibers coexpressing embryonic, fetal, fast and slow, MHC isoforms. In contrast to that observed for the first class, fibers in the second class displayed a normal pattern of expression of desmin, vimentin and titin. (iii) A familial heterogeneity was observed between the 4 patients. The pathological processes involved in the evolution of this syndrome are discussed.

Evolution of muscle specific proteins in Werdnig-Hoffman's disease.

The pattern of expression of desmin, vimentin, titin and different myosin isoforms expressed in atrophic and hypertrophic type I and type II muscle fibers was investigated in 7 biopsies from patients of various ages all diagnosed as suffering from Werdnig-Hoffman's disease. The results revealed that there was a progressive atrophy affecting both type I and type II muscle fibers. The proportion of atrophic type II fibers increased with age. These atrophic fibers expressed predominantly fast MHC together with variable amounts of embryonic and fetal abnormal concentrations of desmin, vimentin and titin were also observed in some of these fibers. Hypertrophic type I fibers expressed exclusively slow MHC. These results are in good agreement with the hypothesis that Werdnig-Hoffman's disease is associated with a persistence of slow twitch type I motor units and a loss of phasic type II motor units. They also confirm that the atrophic fibers were frequently immature although embryonic MLC was never detected in these muscles. In addition we have demonstrated that the hypertrophic fibers were not completely normal since they frequently contained abnormal concentrations of desmin and titin at their periphery.

Modulation of slow and fast elbow extensor EMG tonic activity by stretch reflexes in man.

Reflex EMG responses to sudden passive flexion of the elbow were recorded from anconeus and triceps brachii in 5 human volunteers. While the subjects were required not to resist the flexion movement, they were required to maintain an extension torque of 3.5 or 7.0 Nm prior to its onset. Under these isotonic conditions, the latency and amplitude of the reflex activities from anconeus and triceps brachii did not differ significantly, in contrast to the findings of Le Bozec (1986) in actively relaxed subjects. The myotatic/postmyotatic EMG amplitude ratio did not provide a further quantitative way to distinguish between these muscles. The absence of a difference between the reflex activities of a slow (anconeus) and a fast (triceps brachii) muscle is interpreted as resulting from a strong drive of spindle activity on the whole extensor motoneuron pool, which outweights the differences in recruitment due to the differing relative amounts of type I and type II fibres in the two muscles. Differences like those described between finger and calf muscles by other authors are thought to be due to the relative degree of corticalization of these muscles. All short and long latency responses of the muscles increased in magnitude and decreased in latency with increasing background EMG activity as well as with increasing initial length. The position and tonic activity dependency of these responses is explained in terms of alpha-gamma coactivation.

Biochemical and immunocytochemical analysis in chronic proximal spinal muscular atrophy.

Immunocytochemical and biochemical analyses were carried out on patients affected by chronic SMA. Three groups of patients were identified. In group I, the muscle presented a fascicular atrophy; a high percentage of atrophic type II fibers; and fibers expressing fast, slow, embryonic, and fetal myosin isoforms. In group II, the muscle was characterized by atrophic fibers and normal/hypertrophic fibers expressing only slow myosin isoforms. In group III, the muscle was characterized by fiber type grouping and fibers coexpressing fast and slow myosin isoforms but never embryonic or fetal MHC isoforms. The muscles of groups I and III contained both fast and slow myosins whereas group II muscles were predominantly slow by immunocytochemical analysis or only slow by biochemical analysis. In view of these results, immunocytochemical and histochemical analyses could help to classify chronic SMA and help to understand the different pathogenic processes which seem to be related to the maturational stage of the muscle at the age of onset of the disease.

Genetic fine mapping of the Miyoshi myopathy locus and exclusion of eight candidate genes.

Miyoshi myopathy (MM) is an early adult-onset, autosomal recessive disorder characterized by weakness and muscular atrophy starting in the distal muscles. The disease locus has been previously mapped by linkage analysis to chromosome 2p using the microsatellite marker D2S291. Initial haplotype analysis of markers in families from three different origins (North American, Japanese, and Tunisian) suggested that the MM gene is located in a 4-cM region flanked by markers D2S292 on the telomeric side and D2S286 on the centromeric side. To delineate critical recombination events revealing a more refined localization of the MM gene, we have determined the pattern of segregation of 12 marker loci in two consanguineous families of Tunisian origin. In this study we have: (1) detected recombination events with the disease locus in one family, placing the MM gene most likely between markers D2S443 (CHLC.GGAA4D07.1876) and D2S2109; (2) generated a yeast artificial chromosome contig that spans approximately 3.8 megabases and extends from marker D2S358 to marker D2S286; (3) physically mapped 21 polymorphic markers, 5 genes, 3 STSs, and 1 EST within this contig; (4) detected and mapped a new polymorphism within this interval, allowing us to further reduce the MM locus to a 360-kilobase segment; (5) mapped the gene for the cytoskeletal protein beta-adducin within the MM candidate region, failing to find a consistent pattern of mutation of this gene in our MM patients; (6) excluded seven other candidate myopathy genes from the Miyoshi locus.

Generation of a 3-Mb PAC contig spanning the Miyoshi myopathy/limb-girdle muscular dystrophy (MM/LGMD2B) locus on chromosome 2p13.

Miyoshi myopathy (MM) and limb-girdle muscular dystrophy subtype 2B (LGMD2B) map to the same region on chromosome 2p13. To facilitate the cloning of the defective gene causing these two diseases, we used a combination of chromosome walking and expressed sequence tag (EST) screening and identified 864 P1-derived artificial chromosomes (PACs) whose inserts map to the MM/LGMD2B candidate region and surrounding areas. Among them, 139 are from a chromosome 2-specific PAC library and 725 are from a total genomic PAC library. A 3-Mb contig spanning the candidate region for MM/LGMD2B was assembled. This contig contains 200 PACs, 10 known genetic markers, 5 new polymorphic markers, 57 sequence tagged sites (STSs) generated from PAC end fragments, and 4 random STSs. In addition, we mapped 24 ESTs to this contig and excluded 37 ESTs from the contig, thus eliminating them as candidate MM/LGMD2B genes. The high-resolution, sequence-ready PAC contig for the MM/LGMD2B region provides a backbone for the identification of the disease gene(s) and for clarification of the relationship between the two diseases.

Refined mapping and characterization of the recessive familial amyotrophic lateral sclerosis locus (ALS2) on chromosome 2q33.

Amyotrophic lateral sclerosis (ALS) is a progressive degenerative neuromuscular disease that shows familial, autosomal dominant inheritance in 10%-15% of cases. Previous genetic analysis of one large family linked a recessive form of familial ALS (FALS-AR type 3) to the chromosome 2q33-35 region. Using additional polymorphic markers, we have narrowed the size of the linked region to approximately 1.7 cM by linkage and haplotype analysis. We have also established a yeast artificial chromosome contig across the locus that covers an approximate physical distance of 3 million bases. Based on this contig, genes and expressed sequences that map near the 2q33 region have been examined to determine whether they are located within this ALS2 candidate locus. Five identified genes and 34 expressed sequence tags map within the region defined by crossover analysis and merit further consideration as candidate genes for this disease.