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The term 'limb-girdle myasthenia' ( LGM) was first used to describe three siblings with proximal limb weakness without oculobulbar involvement, but with EMG decrement and responsiveness to anticholinesterase medication. We report here that exome sequencing in the proband of this family revealed several sequence variations in genes linked to proximal limb weakness. However, the only mutations that cosegregated with disease were an intronic IVS7-8A>G mutation and the previously reported 3′- UTR c.* 22C>A mutation in GFPT1, a gene linked to LGM. A minigene assay showed that IVS7-8A>G activates an alternative splice acceptor that results in retention of the last seven nucleotides of intron 7 and a frameshift leading to a termination codon 13 nucleotides downstream from the new splice site. An anconeus muscle biopsy revealed mild reduction of the axon terminal size and postsynaptic fold simplification. The amplitudes of miniature endplate potentials and quantal release were also diminished. The DNA of the mildly affected father of the proband showed only the intronic mutation along with sequence variations in other genes potentially relevant to LGM. Thus, this study performed in the family originally described with LGM showed two GFPT1 untranslated mutations, which may cause disease by reducing GFPT1 expression and ultimately impairing protein glycosylation. [ABSTRACT FROM AUTHOR]

The Charcot-Marie-Tooth (CMT) neuropathies are a group of disorders exhibiting neurophysical, pathological and genetic heterogeneity. CMT2 is a diagnostic subtype of this group of disorders characterized by variable expression and age-of-onset and normal or slightly diminished nerve conduction velocities. Previously, linkage and heterogeneity had been reported in CMT2 with linked families localizing to chromosome 1p (CMT2A). Recently a second CMT2 locus has been described on chromosome 7 in a single large CMT2 family (CMT2D). We have performed pedigree linkage analysis on 15 CMT2 families ( N = 371 individuals, 106 affected family members) and have confirmed linkage to chromosome 7. Furthermore, using both admixture and multipoint linkage analysis we show conclusive evidence for additional heterogeneity within this clinical subtype with evidence of families that exclude linkage to both the CMT2D and CMT2A regions. In addition, unlike the previous report we found no abvious consistend clinical differences between the linked family types. [ABSTRACT FROM AUTHOR]

The localization of the gene for the majority of cases of facioscapulohumeral muscular dystrophy is established as 4q35-qter (FSHD1A), although locus heterogeneity has been demonstrated with a minority of families unlinked to 4q. In FSHD1A, the disease is associated with a deletion of 3.3 kb repeats from a tandem repeat located near the as-yet-unidentified gene. This repeat cross-hybridizes with a telomeric region on 10q, making this cross-hybridizing region a feasible candidate gene for FSHD1B. We have tested the most telomeric marker on 10q (sAVA4) and excluded ∼17 cM on either side of this marker as harboring the FSHD1B gene. [ABSTRACT FROM AUTHOR]