Duchenne muscular dystrophy. Genetic aspects, carrier detection and antenatal diagnosis

Prevalence of Duchenne muscular dystrophy in Italy: a nationwide survey

PURPOSE

The availability of care recommendations has improved survival and delayed the progression of clinical signs in Duchenne muscular dystrophy. The aim of the study was to perform a nationwide survey investigating the prevalence, age distribution, and functional status of Duchenne muscular dystrophyin Italy.

METHODS

The survey was performed by collecting data from all 31 reference centers for Duchenne muscular dystrophy in Italy using a structured form. We assessed age distribution, motor function, and the need for respiratory and nutritional support to evaluate their prevalence in different age and functional subgroups.

RESULTS

The estimated prevalence was 1.65/100,000 (3.4/100,000 males). There were 972 boys and adults with a confirmed diagnosis of Duchenne, of age ranging between 6 months and 48 years (mean = 16.5). Over 59% were below the age of 18 years and the remaining 41% were adults. Over 43% were ambulant and 57% non-ambulant; 14.7% were steroids naive (mean 20.6 years), 75% are currently on steroids (mean 14.6 years) with 604 on the daily regime, 126 intermittent. Nearly 73% did not require any ventilatory support, 16% had NIV ≤ 12 h, 9% > 12 h, and 1.4% had a tracheostomy. More than 82% did not require any nutritional support, 13% required food modification/semisolid and 4.4% had a G-tube.

CONCLUSIONS

Our findings provide information to be used not only for epidemiological purposes but also for possible trial design to include older non-ambulant patients who until recently have been excluded and for whom clinical information is limited. What is Known • Duchenne muscular dystrophy is a progressive disorder associated with reduced survival. • As part of the disorder there is also a progressive loss of important milestones, including loss of ambulation, and increased need for respiratory and nutritional support. What is New • Our nationwide survey provides prevalence, age distribution, and functional status for Duchenne muscular dystrophyin Italy including both boys and adults. • Our findings can be used for epidemiological purposes and for possible trial design.

Uncovering the Embryonic Origins of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a severe degenerative muscle disease caused by mutations in the DMD gene, which encodes dystrophin. Despite its initial description in the late 19th century by French neurologist Guillaume Duchenne de Boulogne, and identification of causal DMD genetic mutations in the 1980s, therapeutics remain challenging. The current standard of care is corticosteroid treatment, which delays the progression of muscle dysfunction but is associated with significant adverse effects. Emerging therapeutic approaches, including AAV-mediated gene transfer, CRISPR gene editing, and small molecule interventions, are under development but face considerable obstacles. Although DMD is viewed as a progressive muscle disease, muscle damage and abnormal molecular signatures are already evident during fetal myogenesis. This early onset of pathology suggests that the limited success of current therapies may partly be due to their administration after aberrant embryonic myogenesis has occurred in the absence of dystrophin. Consequently, identifying optimal therapeutic strategies and intervention windows for DMD may depend on a better understanding of the earliest DMD disease mechanisms. As newer techniques are applied, the field is gaining increasingly detailed insights into the early muscle developmental abnormalities in DMD. A comprehensive understanding of the initial events in DMD pathogenesis and progression will facilitate the generation and testing of effective therapeutic interventions.

Management of respiratory complications and rehabilitation in individuals with muscular dystrophies: 1st Consensus Conference report from UILDM - Italian Muscular Dystrophy Association (Milan, January 25-26, 2019)

Respiratory complications are common in the patient with muscular dystrophy. The periodic clinical and instrumental respiratory evaluation is extremely important. Despite the presence in the literature of updated guidelines, patient associations often report lack of knowledge of these pathologies, particularly in peripheral hospitals. The purpose of this work, inspired by the Italian Muscular Dystrophy Association (UILDM) is to improve management of respiratory problems necessary for the management of these patients complex. To this end, the main items that the specialist can meet in the follow-up of these pathologies have been analyzed and discussed, among which the respiratory basal evaluation, the criteria of adaptation to non-invasive ventilation, management of bronchial secretions, situations of respiratory emergency, indications for tracheostomy and the subject of advance directives of treatment (DAT).

Evolution of life expectancy of patients with Duchenne muscular dystrophy at AFM Yolaine de Kepper centre between 1981 and 2011

OBJECTIVES

Retrospective study over the last 30 years of life expectancy in patients suffering from Duchenne muscular dystrophy (DMD). Analysis of the role of ventilatory assistance and causes of death.

PATIENTS AND METHODS

One hundred and nineteen adult DMD patients were hosted during 1981 to 2011 at AFM Yolaine de Kepper centre, Saint-Georges-sur-Loire, France. Patients' life expectancy was calculated using Kaplan-Meier model.

RESULTS

Life expectancy without or with ventilatory assistance was 22.16 and 36.23 years, respectively. Similarly, life expectancy of patients born from 1970 (mostly with ventilatory assistance) was 40.95 years old from 1970 and 25.77 years old before 1970. Causes of death changed. Cardiac origins of death have increased from 8% to 44%.

CONCLUSION

Ventilator assistance, in this study mostly through tracheotomy prolongs by more than 15 years life expectancy of DMD patients. It allows conservation of a satisfactory quality of life, and should be systematically proposed to patients.

Genetics of neuromuscular disorders

Neuromuscular disorders affect the peripheral nervous system and muscle. The principle effect of neuromuscular disorders is therefore on the ability to perform voluntary movements. Neuromuscular disorders cause significant incapacity, including, at the most extreme, almost complete paralysis. Neuromuscular diseases include some of the most devastating disorders that afflict mankind, for example motor neuron disease. Neuromuscular diseases have onset any time from in utero until old age. They are most often genetic. The last 25 years has been the golden age of genetics, with the disease genes responsible for many genetic neuromuscular disorders now identified. Neuromuscular disorders may be inherited as autosomal dominant, autosomal recessive, or X-linked traits. They may also result from mutations in mitochondrial DNA or from de novo mutations not present in the peripheral blood DNA of either parent. The high incidence of de novo mutation has been one of the surprises of the recent increase in information about the genetics of neuromuscular disorders. The disease burden imposed on families is enormous including decision making in relation to presymptomatic diagnosis for late onset neurodegenerative disorders and reproductive choices. Diagnostic molecular neurogenetics laboratories have been faced with an ever-increasing range of disease genes that could be tested for and usually a finite budget with which to perform the possible testing. Neurogenetics has moved from one known disease gene, the Duchenne muscular dystrophy gene in July 1987, to hundreds of disease genes in 2011. It can be anticipated that with the advent of next generation sequencing (NGS), most, if not all, causative genes will be identified in the next few years. Any type of mutation possible in human DNA has been shown to cause genetic neuromuscular disorders, including point mutations, small insertions and deletions, large deletions and duplications, repeat expansions or contraction and somatic mosaicism. The diagnostic laboratory therefore has to be capable of a large number of techniques in order to identify the different mutation types and requires highly skilled staff. Mutations causing neuromuscular disorders affect the largest human proteins for example titin and nebulin. Successful molecular diagnosis can make invasive and expensive diagnostic procedures such as muscle biopsy unnecessary. Molecular diagnosis is currently largely based on Sanger sequencing, which at most can sequence a small number of exons in one gene at a time. NGS techniques will facilitate molecular diagnostics, but not for all types of mutations. For example, NGS is not good at identifying repeat expansions or copy number variations. Currently, diagnostic molecular neurogenetics is focused on identifying the causative mutation(s) in a patient. In the future, the focus might move to prevention, by identifying carriers of recessive diseases before they have affected children. The pathobiology of many of the diseases remains obscure, as do factors affecting disease severity. The aim of this review is to describe molecular diagnosis of genetic neuromuscular disorders in the past, the present and speculate on the future.

Duchenne muscular dystrophy: survival by cardio-respiratory interventions

We describe survival in Duchenne dystrophy by invasive and noninvasive ventilation vs. untreated. Patients were untreated prior to 1984 (Group 1), underwent tracheotomy from 1984 until 1991 (Group 2), and were managed by noninvasive mechanical ventilation and cardioprotective medications subsequently (Group 3). Symptoms, vital capacity, and blood gases were monitored for all and spirometry, cough peak flows, carbon dioxide tension, and oximetry for Group 3. Sleep nasal ventilation was initiated for symptomatic hypoventilation. An oximeter and mechanical cough assistance were prescribed for maximum assisted cough peak flow <300 L/m. Patients used continuous noninvasive ventilation and mechanically assisted coughing as needed to maintain pulse oxyhemoglobin saturation ≥95%. Survival was compared by Kaplan-Meier analysis. The 56 of Group 1 died at 18.6±2.9, the 21 Group 2 at 28.1±8.3 years of age with three still alive, and the 88 using noninvasive ventilation had 50% survival to 39.6 years, p<0.001, respectively. We conclude that noninvasive mechanical ventilation and assisted coughing provided by specifically trained physicians and therapists, and cardioprotective medication can result in more favorable outcomes and better survival by comparison with invasive treatment.

Redirecting Splicing to Address Dystrophin Mutations: Molecular By-pass Surgery

Mutations in the dystrophin gene that prevent synthesis of a functional protein lead to Duchenne muscular dystrophy (DMD), the most common serious childhood muscular dystrophy. The major isoform is produced in skeletal muscle and the size of the dystrophin gene and complexity of expression have posed great challenges to the development of a therapy for DMD. Considerable progress has been made in the areas of gene and cell replacement, yet it appears that any potential therapy for DMD is still some years away. Other approaches are being considered, and one that has generated substantial interest over the last few years is induced exon skipping. Antisense oligonucleotides have been used to block abnormal splice sites and force pre-mRNA processing back to the normal patterns. This approach is re-interpreted to address the more common dystrophin mutations, where normal splice sites are targeted to induce abnormal splicing, resulting in specific exon exclusion. Selected exon removal during processing of the dystrophin pre-mRNA can by-pass nonsense mutations or restore a disrupted reading frame arising from genomic deletions or duplications. Attributes of the dystrophin gene that have hampered gene replacement therapy may be regarded as positive features for induced exon skipping, which may be regarded as a form of by-pass surgery at the molecular level. In humans, antisense oligonucleotides have been more generally applied to down-regulate specific gene expression, for the treatment of acquired conditions such as malignancies and viral infections. From interesting in vitro experiments several years ago, the dystrophin exon-skipping field has progressed to the stage of planning for clinical trials.

Duchenne muscular dystrophy: prolongation of life by noninvasive ventilation and mechanically assisted coughing

OBJECTIVE

To quantitate prolongation of survival for patients with Duchenne muscular dystrophy with the use of noninvasive intermittent positive-pressure ventilation (IPPV) with and without access to a protocol involving mechanically assisted coughing.

DESIGN

In this retrospective review of all patients with Duchenne muscular dystrophy visiting a neuromuscular disease clinic, patients were trained to use mouth piece and nasal IPPV and mechanically assisted coughing to maintain oxyhemoglobin saturation >94% (protocol). Survival was considered prolonged when noninvasive IPPV was required full time.

RESULTS

Ninety-one of 125 patients used noninvasive IPPV part time for 1.9 +/- 1.3 yr, and 51 went on to require it full time for 6.3 +/- 4.6 yr. Of the 31 noninvasive IPPV users who died without access to the protocol, 20 died from respiratory causes and seven died from cardiac causes. None of the 34 full-time noninvasive IPPV users with access to the protocol underwent tracheotomy or died from respiratory complications during a period of 5.4 +/- 4.0 yr, whereas three died from heart failure. Five patients with no breathing tolerance were extubated or decannulated to continuous noninvasive IPPV.

CONCLUSIONS

Noninvasive respiratory aids can prolong survival and permit extubation or decannulation of patients with Duchenne muscular dystrophy with no breathing tolerance.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

Becker muscular dystrophy combined with X-linked Charcot-Marie-Tooth neuropathy

A man was identified with two X-chromosomal neuromuscular disorders, X-linked Charcot-Marie-Tooth disease (CMTX) and Becker muscular dystrophy (BMD). The neuropathy could be tracked in the family and was found to be caused by a mutation in the connexin32 gene on Xq13. 1. The muscular dystrophy was sporadic owing to a de novo deletion in the dystrophin gene located in band Xp21.2. Although these genetic alterations of the same X-chromosome are considered as physically independent, their combination resulted in a unique phenotype with severe wasting of proximal as well as distal muscles and rapid progression of both conditions.

Prevention of pulmonary morbidity for patients with Duchenne muscular dystrophy

STUDY OBJECTIVE

To evaluate the effects of a new respiratory management protocol on respiratory morbidity and hospitalization rates for patients with Duchenne muscular dystrophy (DMD).

DESIGN

A retrospective cohort study.

METHODS

Using a protocol in which oxyhemoglobin desaturation was prevented or reversed by the use of noninvasive intermittent positive pressure ventilation (IPPV) and assisted coughing as needed, the hospitalization rates and days for 24 protocol DMD ventilator users were compared with those of 22 nonprotocol DMD tracheostomy IPPV users.

RESULTS

The 22 conventionally managed patients were hospitalized a mean of 72.2+/-112 days when undergoing tracheostomy. This included a 16.1+/-5.4-day period of translaryngeal intubation. The 24 protocol patients were hospitalized a mean of 6.0+/-2.4 days (p<0.005) when beginning ventilator use. Over their next 126.2 patient-years of ventilator use, the 24 protocol patients had significantly lower rates of hospitalization (p<0.008) and hospitalization days (p<0.005) than had the tracheostomy IPPV users over a 167.2 patient-year period. This is true although 14 of the 24 protocol patients went on to require 24-h noninvasive IPPV for 4.5+/-3.6 years. Five of the 14 have yet to be hospitalized.

CONCLUSION

The use of inspiratory and expiratory aids can prolong survival while significantly decreasing the pulmonary morbidity and hospitalization rates associated with conventional resort to tracheostomy IPPV.

Identification of a point mutation and germinal mosaicism in a Duchenne muscular dystrophy family

Duchenne and Becker muscular dystrophies (DMD and BMD) are allelic X-linked disorders arising from mutations in the (2.4 Mb) dystrophin gene at Xp21. We have applied the reverse transcriptase-polymerase chain reaction (RT-PCR) to identify a larger than normal dystrophin mRNA from a male with Duchenne muscular dystrophy and his younger affected brother. The increased size of the dystrophin mRNA was due to a splice-site mutation at the exon 26:intron 26 junction where a T to G substitution prevented normal RNA processing. A cryptic splice-site, downstream of the mutation, was activated during processing, resulting in the inclusion of 117 bases of intron 26. This insertion introduced an in-frame stop codon into the mature dystrophin mRNA. An allele-specific test was developed to identify the mutation and was applied to this family. Interestingly, the mother of the two affected boys did not carry the mutation, as determined by allele-specific amplification and direct DNA sequence analysis, indicating gonadal mosaicism. Her eldest daughter, designated as a carrier based upon conventional testing and haplotype analysis, also did not carry the family mutation. Initial haplotyping of the family appeared to be straightforward with gonadal mosaicism becoming evident only after allele-specific analysis. The application of linked markers to identify the disease allele for conventional genetic counselling would have been erroneous in this family and highlights the diagnostic power of precise identification of the disease-causing mutation.

Two distinct mutations in a single dystrophin gene: chance occurrence or premutation?

We report on a kindred segregating 2 distinct mutations of a dystrophin gene. DNA analysis showed that the second mutation, a deletion, arose in the same gene carrying the primary defect which produced a Becker phenotype in the affected males. The DNA data for this family are reported and the alternative explanations of chance occurrence and premutation are discussed to explain these unusual findings.

Measurement of serum myoglobin by a turbidimetric latex agglutination method

We evaluated an immunoturbidimetric quantitation for serum myoglobin by the latex agglutination method using an automated biochemical analyzer. This method is rapid, specific, accurate, precise, and has wide dynamic range. The total assay time is 10 min and is performed at 37 degrees C with continuous monitoring at 570 nm. The assay results were compared with radioisotopic immunoassay results and showed a good correlation coefficient, r = 0.99; Y = 0.98 x + 9.3; N = 79. Sera from healthy adults has a myoglobin concentration in the range of 15-80 ng/ml(N = 362). Sex- and age-related differences were observed. The serum myoglobin levels in males and elderly people showed higher concentration than in females and younger people. The peak elevation of serum myoglobin compared with other cardiac markers was observed within 6 hours after onset of chest pain as well as the CK-isoform ratio (MM3/MM1). All of the serum from 21 patients with definite acute myocardial infarction showed increased serum myoglobin levels (100-1200 ng/ml) upon admission and within 6 hours. The results suggest that assays for serum myoglobin levels are helpful in the early diagnosis of acute myocardial necrosis.

Duchenne muscular dystrophy in Tunisia: a clinical and morphological study of 77 cases

Two types of progressive muscular dystrophy occur in Tunisian children. The first type is characterized by normal dystrophin assays and affects girls and boys in an autosomal recessive pattern of inheritance. The second type has the features of the typical Duchenne muscular dystrophy (DMD) and has abnormal dystrophin. Between 1974 and 1986, 77 patients with Duchenne muscular dystrophy were examined, 66 were biopsied. Among affected siblings and within family kindreds, we observed both clinical and histopathological variability. However, there was a close correlation between the clinical condition and the biopsy findings in each case, allowing accurate prediction of the patient's course and probable duration of the disease.

The diagnosis of Duchenne and Becker muscular dystrophies: two years' experience in a comprehensive carrier screening and prenatal diagnostic laboratory

This article describes the diagnostic algorithm being used for the management of the 148 families affected by Duchenne or Becker muscular dystrophy who are known to the Molecular Neurogenetics Laboratory in the Department of Neuropathology, Royal Perth Hospital. In 60 families from whom DNA has been obtained, 41 mutations (39 deletions and two duplications) of the Duchenne muscular dystrophy gene (DMD) have been identified by means of complementary DNA (cDNA) probes. DNA-based screening has clarified the carrier status of 45 at-risk women, and 13 pregnancies have been monitored. In addition, cDNA screening of all relevant patients with autosomal recessive muscular dystrophy, spinal muscular atrophy or limb-girdle muscular dystrophy facilitated the correct diagnosis of Becker muscular dystrophy in three patients.

Estimation of fertility and fitness in Huntington disease in New England

The advent of presymptomatic and prenatal testing in Huntington disease (HD) may change the reproductive behavior of persons at risk for HD. In order to assess future change, an analysis of fertility and reproductive fitness was carried out on 999 affected and 2,253 unaffected offspring from 235 New England families. Ascertainment biases observed for persons born before 1910 and after 1929 reduced the sample to 250 HD cases and 201 unaffected sib controls born between 1910 and 1929. No increase in reproductive rate was found in HD-affected men compared to male control sibs. A small increase in fertility averaging 0.5 child was seen in HD-affected females compared to unaffected females, but this difference was not significant. The increase in mean number of children for HD females is accounted for in part by a small number of affected women who had very large families. No evidence was found to suggest that any increase in reproductive rate for affected persons was related to offspring being born after HD onset. The fitness of both HD-affected and unaffected females was not significantly different from that of the general population of Massachusetts.

Recovery of induced mutations for X chromosome-linked muscular dystrophy in mice

We have used elevated levels of plasma creatine phosphokinase activity to identify muscular dystrophy phenotypes in mice and to screen the progeny of chemical mutagen-treated male mice for X chromosome-linked muscular dystrophy mutations. We were not successful in identifying heterozygous carriers of these induced muscular dystrophy mutations in greater than 8000 progeny. However, we were highly successful in identifying three additional alleles of the characterized mdx locus. These alleles of mdx were recovered from various mutagen-treated males and they occur on an X chromosome that carries flanking markers that allow us to follow the mutations in genetic crosses and in the development of corresponding mutant stocks. These alleles have been designated as mdx2Cv, mdx3Cv, and mdx4Cv. Preliminary data show that mice with mdx2Cv and mdx3Cv mutations have muscular dystrophic phenotypes that do not grossly differ from the characterized mdx mutation. These additional mdx mutations expand the value of mouse models of X chromosome-linked muscular dystrophy and potentially define additional sites of mutation that impair dystrophin expression.

Canine X-linked muscular dystrophy. An animal model of Duchenne muscular dystrophy: clinical studies

The progression of clinical disease and serum creatine kinase (CK) levels in canine X-linked muscular dystrophy (CXMD) was studied in 7 dogs from birth to 12-14 months and in 18 dogs at varying intervals from birth to 8 weeks. One affected male was studied from age 3.5 to 6 years, and all pups were descendants of this dog. A lethal neonatal form was recognized in some pups. In the more typical form, clinical signs of stunting, weakness and gait abnormalities were evident by 6-9 weeks and were progressive, leading to marked muscle atrophy, fibrosis and contractures by 6 months. Serum CK levels were markedly elevated, such that affected pups could be identified by 1 week. CK values increased until 6-8 weeks, then plateaued at approx. 100 times normal. Affected females and beagle-cross dogs were less severely affected than large breed-cross dogs. In the 2 adult dogs with cardiac insufficiency CK levels had decreased to 5-15 times normal. These studies show that CXMD and Duchenne muscular dystrophy have striking phenotypic as well as genotypic similarities. In addition, these studies of CXMD suggest that in females and in smaller dogs the same genetic defect results in a less severe clinical disease.

A simple method for calculating risks before DNA analysis

Calculation of carrier risk of an X linked disease may be performed on a small computer after DNA analysis, but a method for rapid hand estimation of the risk is still useful for a quick check of the results and weighing the relative importance of each element of information, such as the determination of a haplotype. Each risk estimation is a function of a prior risk and the product of likelihood ratios and these terms are derived themselves from parameters such as fitness or the relative mutation rate in male and female gametes. Even if it is often difficult to have strong experimental estimation of these variables, the existence of a normal father or grandfather must be considered whenever male fitness is not null. The likelihood ratio for a woman for not being a carrier, when her father is not affected and her mother has herself a likelihood R for not having the mutated gene, may be expressed as the ratio 2R/(CmR + 1), with Cm being a function of male fitness and relative mutation rate. Cm represents the odds ratio for the mother of a carrier not to be a carrier, given that the father of the known carrier is not affected. This formula can be used recurrently and reduces to 2R/(R + 1) in lethal X linked disease. When likelihood ratios are expressed as an algebraic function, maximum values are easily determined, hence fixing the limits of DNA analysis.

Evidence for a sperm mutation resulting in Duchenne muscular dystrophy

DNA analysis of Xp21 markers in a family with two brothers affected with Duchenne muscular dystrophy (DMD) revealed that the mutation most likely had occurred in a grandpaternal sperm. There is therefore a low risk that the maternal aunts and their daughters are carriers of the DMD gene.

The clinical consequences of X-chromosome inactivation: Duchenne muscular dystrophy in one of monozygotic twins

We have ascertained retrospectively a female patient, one of identical twins, who was diagnosed at age 23 years as having Duchenne muscular dystrophy (DMD). A muscle biopsy at that time showed a pattern in which large areas of destroyed muscle fibers replaced with adipose tissue were interspersed with normal-appearing muscle fascicles. The visualization of Barr bodies in the muscle biopsy, plus the patient's normal menstrual history served to rule out Turner's syndrome. The clinical expression of DMD in only one of monozygotic twins is strongly suggestive of uneven lyonization, with an excess of paternally derived X-chromosomes being inactivated in the patient. This view is supported by the appearance of the muscle biopsy. Twinning may conceivably predispose to uneven lyonization by reducing the size of the muscle cell anlage at the time of X-chromosome inactivation. Alternatively, lyonization may occur before the splitting of the embryonic mass, and by chance, the two embryonic centers could end up with a significantly different proportion of active maternal and paternal X-chromosomes.

Muscular dystrophy in girls with X;autosome translocations

Twenty known cases of X;autosome translocations with breakpoints at Xp21 associated with Duchenne or Becker muscular dystrophy in girls are reviewed. The variable severity described for different persons may reflect differences in X inactivation or in the nature of the genomic target disrupted. High resolution cytogenetic studies on 12 cases indicate breakpoints on the X chromosome at Xp21.1 or Xp21.2. Translocation chromosomes from several of these cases have been isolated in human/mouse somatic cell hybrids. Molecular heterogeneity in the breakpoint positions has been established by probing DNA from these hybrids with a range of cloned sequences known to be located within, or closely linked to, the Duchenne region. The minimum separation between the most distal and the most proximal breakpoints is 176 kb suggesting that, if a single gene is involved, it must be large. Alternatively, the translocations may affect different genes, or confer alterations to regulatory sequences which operate at a distance.

DNA probe analysis for carrier detection and prenatal diagnosis of Duchenne muscular dystrophy: a standard diagnostic procedure

Thirteen marker loci localised on the short arm of the X chromosome are available for use in genetic studies for Duchenne muscular dystrophy (DMD). This large number of probes detecting about 20 RFLPs encouraged us to set up a standard procedure using a sequence of selected probes and restriction enzymes for the diagnosis of DMD families. The application of DNA probe analysis for carrier detection and prenatal diagnosis, involving 61 pedigrees of both familial and isolated cases, has yielded the following results. Carrier detection using flanking markers was possible in more than 75% of the cases (104 out of 136 females) with a reliability of better than 98%. Prenatal diagnosis was possible in 95% of the cases (65 out of 68 proven carriers or women at risk). Twenty-three prenatal diagnoses were performed on male fetuses; 13 appeared to have a low risk for DMD (less than 1%) and thus the pregnancies continued. Seven have since come to term and the male infants have normal CK levels. The genetic distances of the loci relative to the DMD locus and their order on the short arm of the X chromosome were deduced from our total DMD family material and are not significantly different from those reported earlier. For 754 (DXS84) we found a genetic distance of 5 cM with a lod score of +12.4 and 95% confidence limits between 2 and 12 cM. Similar data were obtained for pERT87 (DXS164), suggesting that in our family material both loci are tightly linked. Multiply informative recombination showed that both 754 and pERT87 map proximal to the DMD mutations in the cases studied. The high frequency of DMD mutations and its relation to the observed instability in this part of the genome will be discussed. Unequal crossing over is proposed as one of the mechanisms contributing to the high mutation frequency.

Duchenne muscular dystrophy in a girl with a 45,X/46,XX/47,XXX chromosome constitution

We report on a 4-year-old girl with Duchenne muscular dystrophy (DMD). One of her sisters had grossly elevated serum creatine-kinase and pyruvate-kinase levels, and one of her maternal great uncles was presumptively affected by DMD. Cytogenetic analysis showed a 45,X/46,XX/47,XXX chromosome constitution. The maternally inherited DMD gene is presumed to be present on the single X of the 45,X cell line.

Cytogenetic analysis and muscle differentiation in a girl with severe muscular dystrophy

The uncommon case is described of a girl severely affected with Duchenne muscular dystrophy. Cytogenetic analysis revealed no numerical or structural abnormalities of the X-chromosome in any of the cells examined (leucocytes and myoblasts). No abnormality in morphology, growth pattern or differentiation was observed in the dystrophic muscle cultures as compared with control cultures.

Duchenne muscular dystrophy in a 46 XY female

The most common muscular dystrophy, Duchenne muscular dystrophy (DMD), is an X-linked disorder that ordinarily has full clinical expression only in males. Reports of typical clinical features in females are rare but have occurred with a phenotypically identical autosomal recessive muscular dystrophy as well as in females with X-chromosome abnormalities such as the Turner syndrome. A girl with full expression of DMD due to a 46 XY karyotype is reported, and other clinical conditions in which expression of the DMD gene occurs in females are reviewed.

Cytogenetic heterogeneity of translocations associated with Duchenne muscular dystrophy

Lymphoblastoid cell lines have been established from nine female patients with Duchenne muscular dystrophy who had previously been reported to have chromosome translocations with breakpoints in the Xp21 region. A detailed cytogenetic comparison of prometaphase chromosomes in these cell lines revealed that six of the translocations had X chromosome breakpoints in the sub-band Xp212 and that one further breakpoint could be assigned to either Xp212 or Xp213. These findings confirm and extend previous observations and provide strong evidence for Xp212 as the site of the Duchenne and Becker loci. For the remaining two translocations the simplest explanation for the observed banding pattern is that the X chromosome breakpoint lies a few thousand kilobases away, in the sub-band Xp211. Other explanations which assume breaks in Xp212 combined with complex local chromosome rearrangements are also presented. It is also possible that the altered banding pattern in these two cases is due to the influence of local sequences on the staining or uncoiling properties of the chromatin.

A computer programme to calculate risk in X linked disorders using multiple marker loci

A computer programme package has been written which calculates the genetic risk (recurrence risk) for X linked disorders, incorporating data from multiple probes. The programme can allow new mutation and the incorporation of other predictors of the disease genotype of the subjects in the family.

Screening for Duchenne muscular dystrophy: an improved screening test for creatine kinase and its application in an infant screening program

A kinetic bioluminescence assay with optimized reagent conditions has been developed for application as a screening test for increased creatine kinase (CK) activities in dried blood spots. This test is used for the early detection of Duchenne muscular dystrophy (DMD) in a voluntary CK screening program in West Germany. Of the 176,600 boys tested up to December 31, 1984, 48 who were less than 6 months old had certain or probable DMD (frequency 1: 3679). In 1983 and 1984, the rate of false positive results was 0.016% for a cut-off activity 300 U/liter and 0.061% for a cut-off activity 180 U/liter. Long-term counseling is offered to families of newly detected DMD patients in order to facilitate the aims of the screening program, namely, avoidance of secondary cases in affected families, early professional care for the sick child, and the early opportunity to make the appropriate decisions for a life with an handicapped child. Two types of a benign hereditary blood anomaly were also detected by CK screening (CK-BB inside erythrocytes or thrombocytes).

Applications and limitations of direct DNA analysis in genetic prediction

Direct analysis of DNA has enormous potential for improved carrier detection or exclusion and early prenatal diagnosis in monogenic diseases. The strategy adopted in practice is determined by the fact that in most diseases allelic genetic heterogeneity precludes elucidation of the mutation in all families. Gene tracking asks the question--has a relative or fetus inherited the same relevant chromosome region as a previously affected family member?--and requires a gene-specific or closely linked DNA probe that reveals a restriction fragment length polymorphism (RFLP) in order to do a linkage study within the family. Gene tracking is independent of allelic heterogeneity in the disease, but is limited to those families in which key relatives are heterozygous for an RFLP.

Ribosomal protein synthesis in cultured skin fibroblast cells obtained from patients with Duchenne muscular dystrophy

Ribosomes and ribosomal subunits were extracted from cultured skin fibroblasts from patients with Duchenne muscular dystrophy (DMD). A poly(U)-directed polyphenylalanine synthesis system was used to test 80S ribosomes from DMD cells and normal controls as well as hybrid 80S couples of subunits from DMD cells and control cells. The activity of ribosomes extracted from the patients was 38-62% lower than that of normal controls. Of the 80S hybrid ribosomes, only those consisting of 40S subunits from DMD cells and 60S subunits from the control cells, showed a similar decrease in activity. That means that the defect is exclusively based on an alteration in the small ribosomal subunit.

Molecular genetics of the human X chromosome

The human X chromosome will soon be mapped at 10 cM intervals. This will permit the localisation of any X linked disorder provided that informative families are available for linkage analysis. The location of RFLPs currently in use for clinical diagnosis is summarised. The next decade should witness the elucidation of the molecular basis of some of the more common defects, such as the muscular dystrophies and X linked mental retardation.

Evaluation of carrier detection of Duchenne muscular dystrophy using carbonic anhydrase III and creatine kinase

Carbonic anhydrase III (CAIII) and creatine kinase (CK) were measured in plasma samples from a series of females at-risk as carriers of Duchenne muscular dystrophy and compared with control groups. Both plasma CAIII and CK levels were raised in a proportion of carriers. Although measurement of CAIII and CK was no more successful in identifying carriers than CK alone, CAIII could fulfill a useful confirmatory role, particularly for cases with a marginally elevated CK or where the sample is poorly preserved. The difference between the CK and CAIII results could indicate biochemical heterogeneity in the expression of Duchenne muscular dystrophy.

Human X chromosome markers and Duchenne muscular dystrophy

Two DNA markers, a random DNA fragment 754 and the cDNA sequence encoding the gene for ornithine transcarbamylase (OTC) have been studied in kindreds segregating for Duchenne muscular dystrophy. 754 and OTC are located close physically to the mutation in the region Xp21 below the breakpoints in two Duchenne females. The genetic distance was found to be approximately 10cM between 754 and DMD (two crossovers in 26 meioses) and to be approximately 10cM between OTC and DMD (two crossovers in 26 meioses). Physical data suggest the order DMD-754-OTC. The frequency of recombination compared to physical distance between these markers and DMD suggests that there may be a hot spot of recombination. The relevance of these observations for the isolation of the DMD mutation and clinical use of these probes is discussed.

Computed tomographic findings in manifesting carriers of Duchenne muscular dystrophy

Clinical and computed tomographic (CT) findings in 3 manifesting carriers of Duchenne muscular dystrophy are reported. CT proved to be an important adjunct to the clinical examination: in all our 3 cases a decrease in density was found in various non-paretic muscles.

Plasma phosphoglycerate mutase as a marker of muscular dystrophy

An elevation of phosphoglycerate mutase (PMG) has been detected in the blood plasma of the genetically dystrophic chicken and in Duchenne muscular dystrophy (DMD) patients. In the dystrophic chicken, plasma PGM in the pectoral muscle was simultaneously depressed to less than one-half that of the normal chicken. In a group of 9 DMD patients, plasma PGM activity was found to be significantly raised above the normal range. A survey of a small group of plasma specimens from human fetuses at risk for muscular dystrophy also suggested that PGM merits investigation as a potential adjunct to other diagnostic indices.

A rapid screening test for Duchenne muscular dystrophy using dried blood specimens

A very simple fluorescent spot screening test for the detection of elevated creatine kinase activity in dried blood specimens is described. The assay uses reagents commercially available in kit form and modifies the procedure for use with whole blood spotted on filter paper. Additional amounts of diadenosine pentaphosphate had to be added to the reaction mixture to inhibit the excess adenylate kinase present in erythrocytes. The sensitivity and reliability of the test is demonstrated. This qualitative assay has the potential for use as a mass neonatal screening test for Duchenne muscular dystrophy.

Chromosomal location of the co-expressed human skeletal and cardiac actin genes

We have examined the relationship between chromosomal location and regulation of the two human genes encoding the sarcomeric muscle actins. The human genes encoding skeletal alpha-actin and cardiac alpha-actin are co-expressed in both human skeletal muscle and heart. We have subcloned a single-copy DNA fragment from an intervening sequence in the human cardiac alpha-actin gene and a single-copy DNA sequence from the 3' untranslated region of a human skeletal alpha-actin cDNA. Using these two gene-specific probes, we examined DNA isolated from human-mouse somatic cell hybrid lines segregating human chromosomes. We observed the segregation of restriction endonuclease-generated DNA cleavage fragments that hybridize to the two probes. The two striated muscle genes do not co-segregate and are on different autosomes. The human cardiac alpha-actin gene (ACTC) is on chromosome 15 in the q11----qter region whereas the skeletal alpha-actin gene (ACTSK) is on chromosome 1 in the p21----qter region. The co-expression of these two genes is not a function of chromosomal linkage. Neither of these muscle genes can be the primary target resulting in X-linked muscular dystrophies.