Duchenne muscular dystrophy.

Progress in understanding the role of dystrophin raises promising hopes for a treatment for Duchenne muscular dystrophy. In addition, great improvements have been made in the ability to diagnose this disease using simple molecular methods.     

Duchenne muscular dystrophy

Summary By a general survey in the hospitals of northeast Italy, Duchenne cases have been located and identified over a 20-year period.In a more restricted area screening for Duchenne carriers has been carried out in affected families. This procedure made possible an exact estimate of the incidence rate, prevalence rate, and mutation rate in a large sample of population. Prevalence rate was found to be 34x10^-6, incidence rate about 28x10^-5, while mutation rate was found lower than 50x10^-6 by the direct method.The discrepancy between the results obtained by the Haldane formula and those obtained by the direct method for the estimate of the mutation rate is discussed.     

Duchenne muscular dystrophy

Summary In an extensive epidemiological survey of Duchenne muscular dystrophy carried out in Venetia (Italy) the incidence was found to be 28.2×10^-5 and female gamete mutation rate was estimated by the direct method between 61 and 35×10^-6. The percentage of isolated cases was 0.54. Indirect and direct estimates of this proportion suggest, however, that only a minor fraction arises from maternal mutation (from 0.11 to 0.18 of the total number of cases). Studies on pedigrees collected in the course of the survey indicate that there is a higher frequency of Duchenne carrier females than normal females in affected sibships. Additional evidence supporting the hypothesis of a reproductive heterozygote advantage and gametic selection is reported.This work was supported by an MDA grant and by funds from the Italian Muscular Dystrophy Assoc. (UILDM)     

Duchenne muscular dystrophy

Summary A segregation analysis on 135 Duchenne families from Venetia (Italy) suggests that the proportion of sporadic cases might be less than expected. Support for this view is also given by an analysis of a pooled sample including 284 additional sibships from comparable studies published previously. Several hypotheses were tested: the maximum likelihood was obtained for a segregation frequency p=0.46 and for a proportion of sporadic cases x=0.227±0.048.Dedicated to Professor G. Montalenti in the occasion of his 80th birthday     

Drug discovery for Duchenne muscular dystrophy via utrophin promoter activation screening

Background

Duchenne muscular dystrophy (DMD) is a devastating muscle wasting disease caused by mutations in dystrophin, a muscle cytoskeletal protein. Utrophin is a homologue of dystrophin that can functionally compensate for its absence when expressed at increased levels in the myofibre, as shown by studies in dystrophin-deficient mice. Utrophin upregulation is therefore a promising therapeutic approach for DMD. The use of a small, drug-like molecule to achieve utrophin upregulation offers obvious advantages in terms of delivery and bioavailability. Furthermore, much of the time and expense involved in the development of a new drug can be eliminated by screening molecules that are already approved for clinical use.

Methodology/Principal Findings

We developed and validated a cell-based, high-throughput screening assay for utrophin promoter activation, and used it to screen the Prestwick Chemical Library of marketed drugs and natural compounds. Initial screening produced 20 hit molecules, 14 of which exhibited dose-dependent activation of the utrophin promoter and were confirmed as hits. Independent validation demonstrated that one of these compounds, nabumetone, is able to upregulate endogenous utrophin mRNA and protein, in C2C12 muscle cells.

Conclusions/Significance

We have developed a cell-based, high-throughput screening utrophin promoter assay. Using this assay, we identified and validated a utrophin promoter-activating drug, nabumetone, for which pharmacokinetics and safety in humans are already well described, and which represents a lead compound for utrophin upregulation as a therapy for DMD.     

Germinal mosaicism in Duchenne muscular dystrophy

Summary We have identified a Duchenne muscular dystrophy (DMD) pedigree where the disease is associated with a molecular deletion within the DMD locus. We have examined the meiotic segregation products of the common female ancestor using marker restriction fragment length polymorphisms (RFLPs) detected by probes that lie within this deletion. These studies show that this female has transmitted three distinet types of X chromosome to her offspring. This observation may be explained by postulating that the mutation arose as a postzygotic deletion within this common ancestor, who was consequently germinally mosaic.     

Deletion screening of the Duchenne muscular dystrophy locus via multiplex DNA amplification.

The application of recombinant DNA technology to prenatal diagnosis of many recessively inherited X-linked diseases is complicated by a high frequency of heterogeneous, new mutations (1). Partial gene deletions account for more than 50% of Duchenne muscular dystrophy (DMD) lesions, and approximately one-third of all cases result from a new mutation (2-5). We report the isolation and DNA sequence of several deletion prone exons from the human DMD gene. We also describe a rapid method capable of detecting the majority of deletions in the DMD gene. This procedure utilizes simultaneous genomic DNA amplification of multiple widely separated sequences and should permit deletion scanning at any hemizygous locus. We demonstrate the application of this multiplex reaction for prenatal and postnatal diagnosis of DMD.     

Sporadic cases in Duchenne muscular dystrophy

Summary A new estimation of the proportion of sporadic cases in Duchenne muscular dystrophy was attempted by means of segregation analysis in a sample of 988 sibships collected on a world-wide scale by different authors. Maximum likelihood estimates of ascertainment probability (), segregation frequency (p), and frequency of sporadic cases (x) were calculated by Morton's equations under different hypotheses. The best fit was found for p=0.454±0.024 and x=0.235±0.034. The possibility that the proportion of sporadic cases might be lower than the expected 1/3 is suggested.     

Hypokalemia complicating Duchenne muscular dystrophy

Although patients with Duchenne muscular dystrophy (DMD) have been shown to have decreased total body potassium levels, serum potassium levels have generally been though to be within normal limits. We report two siblings with DMD noted to be hypokalemic in conjunction with a respiratory illness. Hypokalemia may have exacerbated the pre-existing pulmonary insufficiency in these patients. The literature concerning hypokalemia and DMD is reviewed, and recommendations for the closer monitoring of serum potassium levels in patients with DMD are presented.     

Plasma lipoproteins in Duchenne muscular dystrophy

Plasma lipoproteins of Duchenne muscular dystrophy patients and carriers of the disease, together with age- and sex-matched controls, were examined by density gradient ultracentrifugation and agarose gel electrophoresis. Analysis of density gradient profiles revealed a significant reduction in absorbance (435 nm) by low density and high density lipoproteins from Duchenne patients when compared with controls. Although no abnormalities were observed on electrophoresis of whole plasma samples, the isolated low density lipoprotein fractions from Duchenne patients and carriers displayed increased electrophoretic mobility compared with controls. The results obtained implicate the plasma lipoproteins, in particular the low density lipoproteins, as the primary site of the lesion in this disease.