Linkage in tibial muscular dystrophy (TMD) on chromosome 2q31–33

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Abstracts

DMO3 Refinement of the linkage region of the distal myopathy MPD1 and exclusion of candidate genes N. Binz a, K. Nowak a, A. Butlera, C. Meredith ~'b, N.G. Laing" "Australian Neuromuscular Research Institute, QE 11 Medical Centre, Nedlands, Western Australia 6009, Australia, bCentre for Human Genetics, Edith Cowan Universi~, Joondalup, Western Australia 6027, Australia

The autosomal dominant distal myopathy MPDI was localised to chromosome 14q11.2-13 between the markers D14S72 and D14S49, a distance of 27cM, in 1995 [Laing et al., Am J Hum Genet 1995;56:422-427]. Screening of microsatellite markers to refine the linkage region is ongoing and currently the centromeric boundary has been moved to Dl4S283: a reduction in the linkage region of 5cM. The expressed sequence tag (EST) and UniGene databases at the National Center for Biotechnology Information (NCBI; http://www.ncbi.nlm.nih.gov/) have been used to identify candidate genes for MPD1. Utilising the whole chromosome (Corriell Cell Repository), the Genebridge 4 (Whitehead Institute) and the Stanford G3 (Stanford Human Genome Center) radiation hybrid panels, we have been able to exclude the chromosome 14 genes PAX9, cofilin and Ibd2 (Sel-l) from the linkage region for MPD1. PAX9 has been localised between the markers D14S576 and D14S1053 - 36cM telomeric of the centromere and 9cM telomeric of D14S49. Cofilin was linked to D14S1351 just telomeric to D14S49 and therefore outside the MPDI linkage region. Finally, Ibd2, a muscle protein gene localised to chromosome 14, but not placed on a radiation hybrid map, was excluded from the linkage region. The Genebridge 4 and Stanford G3 radiation hybrid panels linked Ibd2 to the markers WI-4849 and D14S1000, which are adjacent to each other 90cM telomeric of the centromere. The screening of identified but non-localised skeletal muscle genes continues using radiation hybrid mapping.

Keywords: MPDI; Radiation hybrid mapping; Candidate genes

DMO4 Early onset autosomal dominant myopathy with external ophthalmoplegia and rimmed vacuoles in muscle fibers N. Dafin a, M. Kyllermana, J. Wahlstrtm b, T. Martinssonb, A. Oldfors c aDepartments of Pediatrics, bClinical Genetics and CPathology, Sahlgrenska University Hospital, GOteborg, Sweden

Keywords: Hereditary inclusion body myopathy; Joint contractures; Ophthalmoplegia

DMO5 LGMD 2E in Tunisia is caused by a missense mutation Arg91Leu in/3sarcoglycan C. B6nnemanna, J. Wong a, C. Ben Hamida b, M. Ben Hamida b, F. Hentati b, L. Kunkel a "Division of Genetics and Howard Hughes Medical Institute, Children's Hospital and Harvard Medical School, Boston, MA, USA, blnstitut National de Neurologie, Tunis, Tunisia The sarcoglycan complex co-purifies with dystrophin from sarcolemmal preparations and can be separated further from the other dystrophinassociated proteins. Currently, the sequences of four sarcoglycans (~, 8, % 6) are known, and the deduced structures predict single membrane-spanning glycosylated proteins. Four of the currently recognized autosomal recessive limb-girdle muscular dystrophies (LGMD type 2C-F) are caused by mutations in the genes encoding these components of the sarcoglycan complex. LGMD 2C, caused by mutations in "y-sarcoglycan, is prevalent in northern Africa, especially in Tunisia, where this type of muscular dystrophy was originally described. Although the disease appeared genetically fairly homogeneous in this region, e~-sarcoglycan mutations (LGMD 2D) have also been detected. We have now identified the first Tunisian family with severe LGMD 2E, further adding to the genetic heterogeneity of autosomal recessive LGMD in this population. The genetic defect in the pedigree was identified by linkage analysis to markers D4S399 and D4S395; affected members were homozygous at these loci. Direct sequencing of the ~-sarcoglycan gene revealed a homozygous mutation (G272 ---) T, Arg91Leu) in exon 3. This change affects the same arginine residue in the immediate extracellular domain of the protein that was mutated to a proline (G272 ~ C, Arg91Pro) in a Brazilian family with a similarly severe form of the disease, lmmunohistochemical analysis for the sarcoglycan complex demonstrates disintegration of the complex with total absence of all tested sarcoglycans in both of these families. We postulate that the immediate extracellular domain of/3-sarcoglycan may be important for the assembly and/or maintenance of this complex, potentially mediated by the single cysteine residue in that domain. In addition, we have developed a simple 'amplification resistant mutation detection system' (ARMS) for this new Tunisian/3-sarcoglycan mutation, allowing for easy mutation screening in the north African and Mediterranean muscular dystrophy population.

Keywords: /3-Sarcoglycan; LGMD 2E; Tunisia We describe a new myopathy in a large Swedish family with 17 affected cases. Inheritance was autosomal dominant with full penetrance. Characteristic clinical features were joint contractures at birth which normalized during infancy, mild limb-girdle muscle weakness in childhood and muscle atrophy mainly affecting the gluteal and quadriceps muscles in adults. Ophtbalmoplegia, ranging from slight upward gaze palsy in small affected children to an almost complete restriction of mobility in several of the affected adults, was present in 16 cases. Delayed early speech development was found in 5 of the affected children. Tremor of the hands was observed in 7 cases. Onset was in the newborn period in the majority of individuals. The course was progressive in adulthood with a 6 - 7 fold increase of S-CK in two cases. Electrophysiological investigastions showed myopathic changes in examined cases. Characteristic muscle-morphological features in childhood were focal disorganization of myofilaments. Among the studied cases, the three oldest patients, aged 50, 44 and 38 years, respectively showed the most pronounced histopathological changes with increase of the interstitial connective tissue, marked fiber caliber variation of the muscle fibers and frequent central nuclei. Rimmed vacuoles were also found in these three cases together with sarcoplasmic, and in one also intranuclear, 15-21 nm filamentous inclusions. Occasional congophilic inclusions and accumulations of ubiquitin were features suggesting that this myopathy should be grouped with the hereditary inclusion body myopathies.

DMO6 Mechanism of the 4q35 rearrangement in facio-scapulo-humeral muscular dystrophy (FSHD): sequence homology of 4qter and 10qter loci favors the instability of subtelomeric KpnI repeats Luciano Felicetti, Giancarlo Deidda, Enzo Ricci, Giuliana Galluzzi, Stefania Cacurri, Barbara Merico, Serenella Servidei, Luca Colantoni, Pietro Tonali Institute of Cell Biology CNR, Institute of Neurology, Catholic University, UILDM, Rome, Italy The FSHD gene is tightly linked to a 4q35 polymorphic locus containing a single copy sequence (pl 3E- 11 ) and a variable number of 3.3kb KpnI repeat units. It appears that the disease is associated with the deletion of an integral number of Kpn repeats, probably due to crossover within homologous 4q35 regions. Restriction mapping and in situ hybridization experiments have shown that a high degree of sequence homology exists between the 4q35 locus involved in the pathogenesis of FSHD and a subtelomeric 10qter locus: this interferes with the interpretation of Southern blots of affected subjects. We have developed a simple and reliable diagnostic test by using BlnI enzyme that specifically cleaves the 10qter fragments, leaving intact the 4q35 alleles (3 kb reduction). We studied 90 unrelated FSHD families and observed the presence of EcoRI small frag-