Population frequencies of inherited neuromuscular diseases--a world survey

A survey of the world literature, involving over 150 reported studies, of the population frequencies of various inherited neuromuscular diseases has been carried out. Data are presented for the commoner forms of muscular dystrophy (Duchenne, Becker, facioscapulohumeral, limb girdle), myotonic dystrophy and congenital myotonias, proximal spinal muscular atrophies, and the hereditary motor and sensory neuropathies. A conservative estimate of the overall prevalence among both sexes is around 286 x 10(-6), that is 1 in 3500 of the population may be expected to have a disabling inherited neuromuscular disease presenting in childhood or in later life. If severe disorders manifest only in infancy and early childhood (e.g. Werdnig-Hoffmann disease and severe congenital muscular dystrophy) and the rare forms of dystrophy and myopathy are also included, then the overall prevalence could well exceed 1 in 3000.

Analysis of deletions in DNA from patients with Becker and Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder for which the biochemical defect is as yet unknown. Recently, two cloned segments of human X-chromosome DNA have been described which detect structural alterations within or near the genetic locus responsible for the disorder. Both of these cloned segments were described as tightly linked to the locus and were capable of detecting deletions in the DNA of boys affected with DMD. In an attempt to determine more precisely the occurrence of these deletions within a large population of DMD patients and the accuracy of one of the segments, DXS164 (pERT87), in determining the inheritance of the DMD X chromosome, the subclones 1, 8 and 15 were made available to many investigators throughout the world. Here we describe the combined results of more than 20 research laboratories with respect to the occurrence of deletions at the DXS164 locus in DNA samples isolated from patients with DMD and Becker muscular dystrophy (BMD). The results indicate that the DXS164 locus apparently recombines with DMD 5% of the time, but is probably located between independent sites of mutation which yield DMD. The breakpoints of some deletions are delineated within the DXS164 locus, and it is evident that the deletions at the DMD locus are frequent and extremely large.

Unusual type of benign x-linked muscular dystrophy

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Emery-Dreifuss syndrome

Emery-Dreifuss muscular dystrophy is characterised by the triad of (1) early contractures of the elbows, Achilles tendons, and postcervical muscles; (2) slowly progressive muscle wasting and weakness with a humeroperoneal distribution in the early stages; and (3) a cardiomyopathy usually presenting as heart block. The early recognition of the condition is essential because the insertion of a cardiac pacemaker can be life saving. The disorder is usually inherited as an X linked recessive trait (linked to DNA markers around Xq28). However, occasionally it can be inherited as an autosomal dominant trait and there is an indication that this and the X linked form may in some cases have a neurogenic basis. For these reasons it has recently been proposed that the appellation 'Emery-Dreifuss syndrome' be used for this triad of symptoms and signs.

Emery-Dreifuss muscular dystrophy - a 40 year retrospective

Emery-Dreifuss muscular dystrophy (EDMD) was delineated as a separate form of muscular dystrophy nearly 40 years ago, based on the distinctive clinical features of early contractures and humero-peroneal weakness, and cardiac conduction defects. The gene, STA at Xq28, for the commoner X-linked EDMD encodes a 34 kD nuclear membrane protein designated 'emerin', and in almost all cases on immunostaining is absent in muscle, skin fibroblasts, leucocytes and even exfoliative buccal cells, and a mosaic pattern in female carriers. The gene, LMNA at 1q21, for the autosomal dominant Emery-Dreifuss muscular dystrophy encodes other nuclear membrane proteins, lamins A/C. The diagnosis (at present) depends on mutation analysis rather than protein immunohistochemistry. It is still not at all clear how defects in these nuclear membrane proteins are related to the phenotype, even less clear that LMNA mutations can also be associated with familial dilated cardiomyopathy with no weakness, and even familial partial lipodystrophy with diabetes mellitus and coronary heart disease! What began as clinical studies in a relatively rare form of dystrophy has progressed to detailed research into the functions of nuclear membrane proteins particularly in regard to various forms of heart disease.

The nosology of the spinal muscular atrophies

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A family study of Paget's disease of bone

Familial aggregation of Paget's disease of bone occurs occasionally and an exclusively genetic aetiology has been proposed in the past. On the other hand, epidemiological surveys point to an important environmental contribution, and evidence is accumulating to suggest that the disease may be caused by a slow virus infection. Analysis of 407 family history questionnaires completed by patients with Paget's disease confirmed the familial nature of the disease. Overall, the findings were consistent with the hypothesis that Paget's disease is caused by infection with a common and widespread virus superimposed on genetic variation for susceptibility and perhaps severity of the disease.

Clinical studies in benign (Becker type) X-linked muscular dystrophy

Ten extensive families with benign (Becker type) X-linked muscular dystrophy have been studied, in which there was a total of 67 affected males. Reliable information was available on 41 of these males, 29 of whom were alive at the time of the study. The disorder was characterised by a predominantly proximal myopathy, associated with pseudohypertrophy of the calf muscles, particularly in the early stages of the disease. The early development of contractures was not a feature of the disease in these families and cardiac involvement, when present, was a late manifestation. The clinical findings in these patients are discussed in detail and compared with those in a large unselected group of patients with Duchenne muscular dystrophy. The results indicate that the best criterion for distinguishing between these two disorders is the age of becoming chair-bound. Electrocardiographic studies revealed no consistent abnormality and no evidence of an abnormal algebraic sum of the R and S waves in lead V1, as is found in patients with Duchenne muscular dystrophy. Serum creatine kinase levels are significantly elevated, particularly in the early stages of the disease, and in this way preclinical cases may be identified.

Intracellular calcium and pathogenesis and antenatal diagnosis of Duchenne muscular dystrophy

One of the earliest and most important abnormalities of fetal muscle in Duchenne muscular dystrophy is an increase in eosinophilic fibres (those that stain darkly with eosin). A study of normal and at-risk male fetuses after abortion was carried out, which showed that these eosinophilic fibres contain increased intracellular calcium, which suggests that this is an early biochemical change in the disorder. Since increased intracellular calcium would account for various biochemical and clinical features of the disease, it may be related to the primary defect. Thus an increase in muscle fibres containing increased intracellular calcium in at-risk fetuses may provide an additional means of assessing the validity of any future presumptive antenatal test for Duchenne muscular dystrophy.

Communication with parents of children with cancer

The purpose of this study was to assess the receptiveness of parents to information given about their child's life threatening illness. Three months after the child's diagnosis, an independent interviewer, using a structured questionnaire, interviewed the parents about what and how they had been told, and assessed the stage of parental coping reached at that time. All patients were treated at a regional paediatric oncology centre (RHSCE) and the interviews were conducted preferably in the family home (61%), or in a 'quiet' hospital room (39%). Twenty-five, unselected, consecutive patients with cancer and leukaemia diagnosed and treated at the RHSCE and their families were recruited into the study (1988-1989). One child died during the first three months and one single parent family refused co-operation. Eighteen of the 23 interviews conducted were with both parents, and five were with single parents (all maternal). All 23 sets of parents admitted deep shock and devastation on hearing the initial diagnosis, with 12 sets feeling that they had taken in little or none of the information given. A long interview was conducted a few days after the initial talk with the consultant. The parents of four children (17%) denied that the long interview had occurred whilst 10/19 who remembered it expressed specific lack of understanding of some or all details. All families remembered a large number (10-20) of subsequent talks with a wide range of staff, but 14/23 felt that some of the information was still confusing or conflicting, and 9/14 did not want to ask for further clarification, principally because they did not want to hear more bad news. The majority felt the child understood little of what was going on. At the study interview, most parents were assessed as still being very anxious about their child's illness, whilst two couples, one single mother and one father, were content with what and how they had been told about their child's illness and were in a state of emotional homeostasis. It is concluded that communication of bad news is a two-way process requiring skilled medical staff, but also a receptive audience. The emotional state of the parent determines his or her ability to hear and comprehend the information given. The results imply that repetition and clarification at consultation interviews is required until parents are emotionally able to hear, accept and comprehend complex news. Written material, taped interviews and simple videos can assist in this process.

Development and application of an ethically and epidemiologically advantageous assay for the multi-locus microsatellite analysis of Schistosoma mansoni

Non-availability of adult worms from living hosts remains a key problem in population genetic studies of schistosomes. Indirect sampling involving passage through laboratory animals presents significant ethical and practical drawbacks, and may result in sampling biases such as bottlenecking processes and/or host-induced selection pressures. The novel techniques reported here for sampling, storage and multi-locus microsatellite analysis of larval Schistosoma mansoni, allowing genotyping of up to 7 microsatellite loci from a single larva, circumvent these problems. The utility of these assays and the potential problems of laboratory passage, were evaluated using 7 S. mansoni population isolates collected from school-children in the Hoima district of Uganda, by comparing the associated field-collected miracidia with adult worms and miracidia obtained from a single generation in laboratory mice. Analyses of laboratory-passaged material erroneously indicated the presence of geographical structuring in the population, emphasizing the dangers of indirect sampling for population genetic studies. Bottlenecking and/or other sampling effects were demonstrated by reduced variability of adult worms compared to their parent field-collected larval samples. Patterns of heterozygote deficiency were apparent in the field-collected samples, which were not evident in laboratory-derived samples, potentially indicative of heterozygote advantage in establishment within laboratory hosts. Genetic distance between life-cycle stages in the majority of isolates revealed that adult worms and laboratory-passaged miracidia clustered together whilst segregating from field miracidia, thereby further highlighting the utility of this assay.

Genes for super-intelligence?

The results of a postal questionnaire distributed to British members of Mensa failed to confirm an association of superior intelligence with torsion dystonia, retinoblastoma, or phenylketonuria, but were consistent with real associations between high IQ and infantile autism, gout, and myopia. Further confirmation of these findings in other populations might well indicate that genes producing these disorders have more or less direct effects on cerebral development and function.

Duchenne muscular dystrophy--Meryon's disease

In a communication to the Royal Medical and Chirurgical Society of London in December 1851, which was published in the Transactions of the Society the following year, Edward Meryon, an English physician, described, in considerable detail, eight boys in three families with a disease later referred to as Duchenne muscular dystrophy. He was particularly impressed by the predilection for males and its familial nature, and that the progressive muscle wasting and weakness was essentially due to a disease of muscle and not the nervous system. His detailed histological studies revealed no abnormality of the spinal cord or nerves but in muscle tissue he noted extensive "granular degeneration" and in particular that the sarcolemma was broken down and destroyed. He appears to have been the first physician to make a detailed clinical, genetic, and pathological study of the disorder several years before Duchenne.

X-linked muscular dystrophy with early contractures and cardiomyopathy (Emery-Dreifuss type)

The original Virginia family with X-linked muscular dystrophy with early contractures and cardiomyopathy (Emery-Dreifuss type) has been reinvestigated 25 years later. The findings confirm that a cardiomyopathy, presenting most often as atrioventricular block, is a significant feature of the disease, which is characterized by the triad of: 1) slowly progressive muscle wasting and weakness with a humero-peroneal distribution in the early stages; 2) early contractures of the elbows, Achilles tendons, and post-cervical muscles; and 3) a cardiomyopathy usually presenting as heart block (some female carriers may also develop heart block). Other reported families with X-linked Emery-Dreifuss muscular dystrophy as well as a rare autosomal variant are reviewed, and differentiation from scapulo-peroneal muscular dystrophy and the rigid spine syndrome is discussed.

Aryl-hydrocarbon-hydroxylase inducibility in patients with cancer

Aryl-hydrocarbon-hydroxylase (A.H.H.) inducibility has been studied in the peripheral-blood lymphocytes of patients with squamous-cell lung cancer, of patients with cancer at other sites, and of controls matched for age, sex, social class, and smoking habits. The proportion of high inducers was significantly greater among patients with lung cancer (but not patients with other cancers) than among controls, which suggests that, besides smoking, a constitutional factor may be involved in the pathogenesis of lung cancer.

Estimation of proportion of new mutants among cases of Duchenne muscular dystrophy

Using a number of different methods, it is confirmed that approximately one third of all cases of X-linked Duchenne muscular dystrophy are new mutants, the remainder being sons of carriers.

Abnormalities of the electrocardiogram in female carriers of Duchenne muscular dystrophy

The algebraic sum of the R and S waves (R-S) in the V(1) lead of the electrocardiogram has been found to be significantly greater in female carriers of X-linked Duchenne muscular dystrophy (but not in women with limb-girdle muscular dystrophy) compared with normal women of comparable age. A similar E.C.G. abnormality is found in affected boys, and possibly certain carriers have a latent cardiomyopathy and may even be predisposed to cardiac failure.