Myotonic dystrophy (DM) is the most common inherited neuromuscular disease in adults, with a global incidence of 1 in 8000 individuals. DM is an autosomal dominant, multisystemic disorder characterized primarily by myotonia and progressive muscle weakness. Genomic and complementary DNA probes that map to a 10-kilobase Eco RI genomic fragment from human chromosome 19q13.3 have been used to detect a variable length polymorphism in individuals with DM. Increases in the size of the allele in patients with DM are now shown to be due to an increased number of trinucleotide CTG repeats in the 3' untranslated region of a DM candidate gene. An increase in the severity of the disease in successive generations (genetic anticipation) is accompanied by an increase in the number of trinucleotide repeats. Nearly all cases of DM (98 percent or 253 of 258 individuals) displayed expansion of the CTG repeat region. These results suggest that DM is primarily caused by mutations that generate an amplification of a specific CTG repeat.

The attachment of biotin to apocarboxylases is catalyzed by holocarboxylase synthetase (HCS). An inherited deficiency of HCS results in the disorder 'multiple carboxylase deficiency', which is characterized by reduced activity of all biotin-dependent carboxylases. Here we show that the majority of HCS localizes to the nucleus rather than the cytoplasm based on immunofluorescence studies with antibodies to peptides and full length HCS and on the expression of recombinant HCS. Subnuclear fractionations indicate that HCS is associated with chromatin and the nuclear lamina, the latter in a discontinuous distribution in high salt-extracted nuclear membranes. During mitosis, HCS resolves into ring-like particles which co-localize with lamin B. Nuclear HCS retains its biotinylating activity and was shown to biotinylate purified histones in vitro. Significantly, fibroblasts from patients with HCS deficiency are severely deficient in histone biotinylation in addition to the deficiency of carboxylase activities. We propose that the role of HCS in histone modification may be linked to the participation of biotin in the regulation of gene expression or cell division and that affected patients may have additional disease beyond that due to the effect on carboxylases.

Mutations of the human Patched gene ( PTCH ) have been identified in individuals with the nevoid basal cell carcinoma syndrome (NBCCS) as well as in sporadic basal cell carcinomas and medulloblastomas. We have isolated a homologue of this tumour suppressor gene and localized it to the short arm of chromosome 1 (1p32.1-32.3). Patched 2 ( PTCH2 ) comprises 22 coding exons and spans approximately 15 kb of genomic DNA. The gene encodes a 1203 amino acid putative transmembrane protein which is highly homologous to the PTCH product. We have characterized the genomic structure of PTCH2 and have used single-stranded conformational polymorphism analysis to search for mutations in PTCH2 in NBCCS patients, basal cell carcinomas and in medulloblastomas. To date, we have identified one truncating mutation in a medulloblastoma and a change in a splice donor site in a basal cell carcinoma, suggesting that the gene plays a role in the development of some tumours.

The patched gene (Ptc) is a member of the hedgehog signaling pathway which plays a central role in the development of many invertebrate and vertebrate tissues. In addition, Ptc and a number of other pathway members are mutated in some common human cancers. Patched is the receptor for the hedgehog ligand and in the mouse ablation of the Ptc gene leads to developmental defects and an embryonic lethal phenotype. Here we describe a conditional Ptc allele in mice which will have utility for the temporospatial ablation of Ptc function.

SummaryAn in vivo comparative study of sonic, desert and Indian hedgehog reveals that hedgehog pathway activity regulates epidermal stem cell homeostasis