Dystrophin-related protein (DRP or 'utrophin') is localized in normal adult muscle primarily at the neuromuscular junction. In the absence of dystrophin in Duchenne muscular dystrophy (DMD) patients, DRP is also present in the sarcolemma. DRP is expressed in fetal and regenerating muscle and may play a similar role to dystrophin in early development, although it remains to be determined whether DRP can functionally replace dystrophin in adult tissue. Previously we described a 3.5-kilobase complementary DNA clone that exhibits 80 per cent homology to the C-terminal domain of dystrophin. This sequence identifies a 13-kilobase transcript that maps to human chromosome 6 (refs 2, 11). Antibodies raised against the gene product identify a polypeptide with a relative molecular mass of about 400K in all tissues examined. To investigate the relationship between DRP and dystrophin in more detail, we have cloned and sequenced the whole DRP cDNA. Homology between DRP and dystrophin extends over their entire length, suggesting that they derive from a common ancestral gene. Comparative analysis of primary sequences highlights regions of functional importance, including those that may mediate the localization of DRP and dystrophin in the muscle cell.

Genetic studies in patients with severe early-onset obesity have provided insights into the molecular and physiological pathways that regulate body weight in humans. We report a 19-year-old male with hyperphagia and severe obesity, mild learning difficulties and hypogonadism, in whom diagnostic tests for Prader-Willi syndrome (PWS) had been negative. We carried out detailed clinical and metabolic phenotyping of this patient and investigated the genetic basis of this obesity syndrome using Agilent 185 k array comparative genomic hybridization (aCGH) and Affymetrix 6.0 genotyping arrays. The identified deletion was validated using multiplex ligation-dependent probe amplification and long-range PCR, followed by breakpoint sequencing which enabled precise localization of the deletion. We identified a 187 kb microdeletion at chromosome 15q11-13 that encompasses non-coding small nucleolar RNAs (including HBII-85 snoRNAs) which were not expressed in peripheral lymphocytes from the patient. Characterization of the clinical phenotype revealed increased ad libitum food intake, normal basal metabolic rate when adjusted for fat-free mass, partial hypogonadotropic hypogonadism and growth failure. We have identified a novel deletion on chromosome 15q11-13 in an individual with hyperphagia, obesity, hypogonadism and other features associated with PWS, which is normally caused by deficiency of several paternally expressed imprinted transcripts within chromosome 15q11-13, a region that includes multiple protein-coding genes as well as several non-coding snoRNAs. These findings provide direct evidence for the role of a particular family of noncoding RNAs, the HBII-85 snoRNA cluster, in human energy homeostasis, growth and reproduction.

Nine cases are described of a demyelinating peripheral neuropathy that had an onset in infancy. The clinical features conformed to those of type III hereditary motor and sensory neuropathy or Dejerine-Sottas disease. All showed a severe neurological deficit and had profoundly reduced nerve conduction velocities. Amongst these cases we identified four novel point mutations in the peripheral myelin protein 22 (PMP22) gene. These were Ser72Trp, Ser76lle and Leu80Pro. The Ser72Trp mutation was dominantly inherited by a mother and son, both severely affected. Two novel mutations in the gene for P0 myelin protein were also detected. These were Ile134Thr in exon 3, and a complex rearrangement in exon 4. The remaining three patients had presumed autosomal recessive inheritance. In these, no abnormality for the PMP22 and P0 genes was detected and a mutation at another locus or loci seems probable. On nerve biopsy the final two cases were shown to be examples of hereditary neuropathy with focally folded myelin sheaths. One showed both bulbar and diaphragmatic involvement. It is concluded that hereditary demyelinating neuropathy of infancy is genetically heterogeneous. Mutational screening for the PMP22 and P0 genes and nerve biopsy are therefore merited in patients with a childhood demyelinating neuropathy that is more severe than usual and in whom a chromosome 17 duplication is not present.

We have previously reported a dystrophinrelated locus (DMDL for Duchenne muscular dystrophy-like) on human chromosome 6 that maps close to the dy mutation on mouse chromosome 10. Here we show that this gene is expressed in a wide range of tissues at varying levels. The transcript is particularly abundant in several human fetal tissues, including heart, placenta, and intestine. Studies with antisera raised against a DMDL fusion protein identify a 400,000 Mr protein in all mouse tissues tested, including those of mdx and dy mice. Unlike the dystrophin gene, the DMDL gene transcript is not differentially spliced at the 3' end in either fetal muscle or brain.Dystrophin has been identified as the protein product defective in Duchenne muscular dystrophy (DMD); however, very little is known about its precise function (1-3). Sequence comparisons have revealed features in common with cytoskeletal proteins. The amino-terminal region of dystrophin shows homology to the actin binding region of a-actinin (4,5) and the central rod domain shows structural similarities to the triple helical configuration of spectrin (6). In contrast, the carboxyl-terminal domain of 420 amino acids does not show homology to any previously characterized proteins. This latter domain is thought to be important in the integration of dystrophin into a glycoprotein complex localized at the muscle membrane surface (7,8). The carboxyl-terminal region of the gene is differentially spliced in muscle and brain, which suggests the production of isoforms with differing interactions with membrane proteins (9). In addition, this region of dystrophin is important for the correct functioning of the molecule in vivo as deletions covering this domain result in DMD rather than the milder Becker muscular dystrophy (10)(11)(12)(13).Recently, we demonstrated the existence of an mRNA in human fetal muscle that shares a high degree of sequence homology with the carboxyl-terminal region of dystrophin (14). The gene encoding this transcript is localized to human chromosome 6 and the locus has been designated DMDL for DMD-like in Human Gene Mapping 10 (15). The DMDL gene shares structural similarities with dystrophin: the transcript is large, 13 kilobases (kb), and is multiexonic with a similar distribution of 3' exons and introns.Although no human disease has yet been attributed to mutations at the DMDL locus, the mouse homologue of this gene, designated Dmdl, has been shown to be syntenic with the dy (dystrophia muscularis) locus on mouse chromosome 10 (16). The dy mutation is recessive and results in a severe neuromuscular disease in the mouse in which skeletal muscle shows degenerative changes (17). These observations suggest that the Dmdl gene may be a candidate for the dy mutation.In this paper, we present the tissue distribution of the DMDL transcript in humans and compare this distribution with the presence of a 400,000 Mr protein in mouse tissues. We also investigate the occurrence ofthe DMDL polypeptide in liver and muscle of mice with mutations in the dy...

Purpose of ReviewThis review aims to present current information on genes underlying severe obesity, with the main emphasis on the three genes LEP, LEPR and MC4R.Recent FindingsThere is a substantial amount of evidence that variants in at least ten different genes are the cause of severe monogenic obesity. The majority of these are involved in the leptin-melanocortin signalling pathway. Due to the frequency of some of the identified variants, it is clear that monogenic variants also make a significant contribution to common obesity.SummaryThe artificial distinction between rare monogenic obesity and common polygenic obesity is now obsolete with the identification of MC4R variants of strong effect in the general population.

Leptin is emerging as a key regulator of bone remodeling. In a population-based study of 1306 postmenopausal Danish women, nonsynonymous LEPR SNPs were associated with risk of adiposity, BMD, and vertebral fracture. Smoking exacerbates this LEPR-associated fracture risk.Introduction: Nonsynonymous single nucleotide polymorphisms (SNPs) in the human LEPR gene have been associated with adiposity in a number of studies, but there have been no large-scale studies of their implications for BMD and osteoporotic fracture risk in postmenopausal women. Materials and Methods:We carried out a population-based study of 1430 women. Three well-known nonsynonymous leptin receptor (LEPR) SNPs (Lys109Arg, Gln223Arg, and Lys656Asn) were genotyped for qualitative and quantitative association analysis. Phenotype characteristics of main interest were DXA measures of body fat and lean tissue mass, BMD, and radiographic vertebral fractures. Results: Gln223Arg associated with risk of vertebral fracture (overall OR ‫ס‬ 1.76; OR in smokers ‫ס‬ 2.31; p ‫ס‬ 0.0004), in addition to BMD of the femoral neck and total hip (p ‫ס‬ 0.036 and 0.008, respectively). Heterozygote carriers showed lower BMD at both sites. Gln223Arg was also associated with adiposity (p ‫ס‬ 0.001 for total fat mass). For adiposity, the at-risk allele was G (resulting in an arginine at position 223). Conclusions: Variation in LEPR seemed to contribute to the variation in BMD and fracture risk in Danish postmenopausal women; the heterozygous genotype was associated with increased risk of manifest osteoporosis. Further studies are needed to replicate these data and to clarify the mechanisms involved.

Down syndrome (DS; trisomy 21) is associated with a wide range of variable clinical features, one of the most common being congenital heart defects (CHD). We used molecular genetic techniques to study the inheritance of genes on chromosome 21 in children with DS and CHD. Polymorphic markers on the long arm of chromosome 21 were analysed in 99 families who had a child with DS. Of these, 60 children had a CHD and 39 children had no CHD. Heterotrisomy describes the inheritance of an allele from each of three different grandparents. In some cases heterotrisomy will involve the inheritance of three different alleles. Heterotrisomic regions were defined as those showing retention of non-disjoining parental heterozygosity at polymorphic loci in the non-disjoined chromosomes of children with DS. Using polymorphic non-coding markers, we identified a consistent 9.6-cM minimum region (D21S167-HMG14) of heterotrisomy in children with DS and ventricular septal defect (VSD). Comparing individuals with DS and VSD to all others with DS (those either with no CHD or with any other CHD combined) shows the individuals with DS and VSD to have significantly more non-reduction or heterotrisomy in this region (P=0.006, Fisher's exact test, two-tailed). We postulate that heterotrisomy for a gene or genes in this region is a contributing factor to the pathogenesis of VSD in trisomy 21 either through the presence of three different specific alleles or through the presence of specific combinations of alleles.

The important roles of extracellular vesicles in the pathogenesis of various diseases are rapidly being elucidated. As important vehicles of intercellular communication, extracellular vesicles, which comprise microvesicles and exosomes, are revealing important roles in cancer tumorigenesis and metastases and in the spread of infectious disease. The September 2012 Focused Meeting 'Microvesiculation and Disease' brought together researchers working on extracellular vesicles. The papers in this issue of Biochemical Society Transactions review work in areas including HIV infection, kidney disease, hypoxia-mediated tumorigenesis and down-regulation of immune cell functions in acute myeloid leukaemia by tumour-derived exosomes. In all cases, microvesicles and exosomes have been demonstrated to be important factors leading to the pathophysiology of disease or indeed as therapeutic vehicles in possible new treatments. The aim was, having enhanced our molecular understanding of the contribution of microvesicles and exosomes to disease in vitro, to begin to apply this knowledge to in vivo models of disease.