Large-scale population analysis challenges the current criteria for the molecular diagnosis of fascioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a common hereditary myopathy causally linked to reduced numbers (≤8) of 3.3 kilobase D4Z4 tandem repeats at 4q35. However, because individuals carrying D4Z4-reduced alleles and no FSHD and patients with FSHD and no short allele have been observed, additional markers have been proposed to support an FSHD molecular diagnosis. In particular a reduction in the number of D4Z4 elements combined with the 4A(159/161/168)PAS haplotype (which provides the possibility of expressing DUX4) is currently used as the genetic signature uniquely associated with FSHD. Here, we analyzed these DNA elements in more than 800 Italian and Brazilian samples of normal individuals unrelated to any FSHD patients. We find that 3% of healthy subjects carry alleles with a reduced number (4–8) of D4Z4 repeats on chromosome 4q and that one-third of these alleles, 1.3%, occur in combination with the 4A161PAS haplotype. We also systematically characterized the 4q35 haplotype in 253 unrelated FSHD patients. We find that only 127 of them (50.1%) carry alleles with 1–8 D4Z4 repeats associated with 4A161PAS, whereas the remaining FSHD probands carry different haplotypes or alleles with a greater number of D4Z4 repeats. The present study shows that the current genetic signature of FSHD is a common polymorphism and that only half of FSHD probands carry this molecular signature. Our results suggest that the genetic basis of FSHD, which is remarkably heterogeneous, should be revisited, because this has important implications for genetic counseling and prenatal diagnosis of at-risk families.     

Muscle Protein Alterations in LGMD2I Patients With Different Mutations in the Fukutin-related Protein Gene

Fukutin-related protein (FKRP) is a protein involved in the glycosylation of cell surface molecules. Pathogenic mutations in the FKRP gene cause both the more severe congenital muscular dystrophy Type 1C and the milder Limb-Girdle Type 2I form (LGMD2I). Here we report muscle histological alterations and the analysis of 11 muscle proteins: dystrophin, four sarcoglycans, calpain 3, dysferlin, telethonin, collagen VI, α-DG, and α2-laminin, in muscle biopsies from 13 unrelated LGMD2I patients with 10 different FKRP mutations. In all, a typical dystrophic pattern was observed. In eight patients, a high frequency of rimmed vacuoles was also found. A variable degree of α2-laminin deficiency was detected in 12 patients through immunofluorescence analysis, and 10 patients presented α-DG deficiency on sarcolemmal membranes. Additionally, through Western blot analysis, deficiency of calpain 3 and dystrophin bands was found in four and two patients, respectively. All the remaining proteins showed a similar pattern to normal controls. These results suggest that, in our population of LGMD2I patients, different mutations in the FKRP gene are associated with several secondary muscle protein reductions, and the deficiencies of α2-laminin and α-DG on sections are prevalent, independently of mutation type or clinical severity. (J Histochem Cytochem 56:995–1001, 2008)     

Molecular analysis in Brazilian cystic fibrosis patients reveals five novel mutations

We have performed molecular genetic analyses on 160 Brazilian patients diagnosed with cystic fibrosis (CF). Screening of mutations in 320 CF chromosomes was performed through single strand conformation polymorphism (SSCP) and heteroduplex analyses assay followed by DNA sequencing of the 27 exons and exon/intron boundaries of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The frequency of CFTR variants of T-tract length of intron 8 (IVS8 Tn) was also investigated. This analysis enabled the detection of 232/320 CF mutations (72.2%) and complete genotyping of 61% of the patients. The deltaF508 mutation was found in 48.4% of the alleles. Another fifteen mutations (previously reported) were detected: G542X, R1162X, N1303K, R334W, W1282X, G58E, L206W, R553X, 621+1G-->T, V232D, 1717-1G-->A, 2347 delG, R851L, 2789+5G-->A, and W1089X. Five novel mutations were identified, V201M (exon 6a), Y275X (exon 6b), 2686 insT (exon 14a), 3171 delC (exon 17a), and 3617 delGA (exon 19). These results contribute to the molecular characterization of CF in the Brazilian population. In addition, the identification of the novel mutation Y275X allowed prenatal diagnosis in a high-risk fetus.