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

Duchenne muscular dystrophy: pathogenetic aspects and genetic prevention

Duchenne muscular dystrophy (DMD) is the most common sex linked lethal disease in man (one case in about 4000 male live births). The patients are wheelchair bound around the age of 8-10 years and usually die before the age of 20 years. The mutation rate, estimated by different methods and from different population studies, is in the order of 7 X 10(-5), which is higher than for any other X-linked genetic disease. Moreover, unlike other X linked diseases such as hemophilia A or Lesh-Nyhan's disease, there seems to be no sex difference for the mutation rates in DMD. Several observations of DMD in girls bearing X-autosomal translocations and linkage studies on two X chromosomal DNA restriction fragment length polymorphisms indicate that the DMD locus is situated on the short arm of the X chromosome, between Xp11 and Xp22. It may be of considerable length, and perhaps consisting of actively coding and non-active intervening DNA sequences. Thus unequal crossing over during meiosis in females could theoretically account for a considerable proportion of new mutations. However, there is no structurally or functionally abnormal protein known that might represent the primary gene product, nor has any pathogenetic mechanism leading to the observed biochemical and histological alterations been elucidated. Among the numerous pathogenetic concepts the hypothesis of a structural or/and functional defect of the muscular plasma membrane is still the most attractive. It would explain both the excess of muscular constituents found in serum of patients and carriers, such as creatine kinase (CK), as well as the excessive calcium uptake by dystrophic muscle fibres, which, prior to necrosis, could lead to hypercontraction, rupture of myofilaments in adjacent sarcomeres and by excessive Ca uptake to mitochondrial damage causing crucial energy loss. The results of studies on structural and functional membrane abnormalities in cells other than muscle tissue, e.g., erythrocytes, lymphocytes and cultured fibroblasts, indicate that the DMD mutation is probably demonstrable in these tissues. However, most of the findings are still difficult to reproduce or even controversial. DMD is an incurable disease; therefore most effort, in research as well as in practical medicine, is concentrated upon its prevention.(ABSTRACT TRUNCATED AT 400 WORDS)

The enzymology of skeletal muscle disorders

In myopathic disorders, abnormal serum enzyme activities are seen primarily in diseases of skeletal muscle where the condition involves the muscle fibers themselves. In denervation myopathies, serum enzyme activities are usually normal. The most dramatic increases of serum enzymes, particularly creatine kinase, are found in the dystrophic diseases, particularly Duchenne dystrophy. A review is given here of the many causes of abnormal serum enzyme activities where the source of enzymes is believed to be skeletal muscle. These include the dystrophies, various types of trauma, exercise, drug- and poison-induced causes including alcohol, malignant hyperthermia, inflammatory diseases, and miscellaneous causes. Tissue and serum activities are summarized for the commonly performed serum enzymes, i.e., CK, LD, AST, and aldolase. An extensive tabular and current description of the various types of dystrophies is given along with serum CK and pyruvate kinase activities.

Detection of carriers of X-linked gene for Duchenne muscular dystrophy by levels of creatine kinase and pyruvate kinase

Creatine kinase (CK) is the enzyme most often utilized for the detection of carriers of the gene for X-linked muscular dystrophies. In 1974, pyruvate kinase (PK) levels were also found to be increased in these carriers. The objective of the present study, carried out on 77 women related to patients with Duchenne muscular dystrophy (DMD), was to compare the efficiency of the two enzymes in the detection process. Of the 11 obligate heterozygotes for the DMD gene in the group, 8 exhibited elevated mean CK levels, 6 had elevated mean PK levels, and 9 had elevated mean levels of at least one of the enzymes. Among the mothers of isolated patients, 2/13 had elevated mean CK levels, 3/13 had elevated mean PK levels, and 5/13 had elevated mean levels of at least one of these enzymes. Thus, the study confirms data obtained by other investigators indicating that the use of PK can increase the detection rate of carriers of the gene for X-linked muscular dystrophies.

Prospective study of X-linked progressive muscular dystrophy in Campania

Within the Campania region of southern Italy a prospective study on X-linked progressive muscular dystrophy was conducted over a period of 12 years from 1969 to 1980, inclusive. The mean incidence rate was 21.7 per 100,000 male livebirths for Duchenne muscular dystrophy (DMD) cases and 3.2 per 100,000 male livebirths for Becker muscular dystrophy (BMD) cases. The familial cases were 38.5% among the DMD patients and 50% among the BMD patients. Myocardial involvement appeared in DMD patients at about 6 years of age in a high percentage of cases and increased progressively until the last years of life, when cardiac damage occurred in 95% of cases. The percentage of myocardial involvement in BMD patients was very low before 13 years of age, but increased progressively until 20 years, when cardiac damage occurred in 80% of cases studied; severe cardiomyopathy did not occur before the age of 21. The data reported also include the effects of age on physical performance, serum creatine kinase activity and serum myoglobin levels, the types of cardiac damage, and the causes of death.

Possible manifestation of the dystrophic X chromosome in muscle cultures from carriers of Duchenne muscular dystrophy

Multilayer cell clusters have been observed before confluence and before myotube formation in muscle cell cultures derived from open biopsies of 7 of 14 (50%) female carriers of Duchenne muscular dystrophy, and in a high percentage of other dystrophic cultures. By contrast, this abnormality was seen in only 12 of 204 (6%) muscle biopsies from patients with other neuromuscular disorders. It appears that cluster formation is independent of the amount of connective tissue present in vivo, because histopathological analysis of the carrier biopsies showed increased endomysial connective tissue in only two cases. These results suggest that cluster formation is an expression of a myogenic defect and that it may be a manifestation of the genetic abnormality in X-linked muscular dystrophy.

Severe autosomal recessive muscular dystrophy in an extended Sudanese kindred

The clinical manifestations, biochemical, electrocardiographic, histological and histochemical features of a severe autosomal recessive muscular dystrophy (MD)--as seen in 15 members of a large Sudanese kindred, both male and female--are reported and discussed. The age of onset ranged from three to five years, the pattern of muscular weakness was similar to that of Duchenne MD and pseudohypertrophy was a remarkable feature. Both sexes became completely dependent by 16 years, and died at or before 20 years of age. The clinical picture in this family and the histological features are compared with those of Duchenne MD and with cases reported from Tunisia, Qatar and Libya. Certain clinical and histological features distinguish all of these types from each other and from the milder autosomal recessive MD of childhood which is more usual in the United Kingdom, Europe, Australia and North America.

Complex segregation analysis and computer-assisted genetic risk assessment for Duchenne muscular dystrophy

Two hundred forty-four Toronto pedigrees of Duchenne muscular dystrophy patients have been partitioned into nuclear families with pointers for complex segregation analysis under a mixed model. The model takes into account the major X-linked locus and a multifactorial transmissible component for creatine kinase activity in females. The incidence in the province of Ontario is estimated to be 292 per million male births. The proportion of sporadic cases is 1/3, demonstrating equal mutation rates in males and females. A multifactorial component (H = 0.379) contributes to family resemblance for creatine kinase measurements. Examples are presented of the application of a computer program, COUNSEL, to derive genetic risks for genetic counseling with consideration of the multifactorial component.

Duchenne muscular dystrophy carrier detection using logistic discrimination: serum creatine kinase, hemopexin, pyruvate kinase, and lactate dehydrogenase in combination

In the absence of an unambiguous test for identifying Duchenne muscular dystrophy (DMD) heterozygotes, methods are needed for combination of the results of individually equivocal tests as effectively and rationally as possible. Tw used logistic discrimination to assess the effectiveness of measurements of serum creatine kinase, hemopexin, pyruvate kinase, and lactate dehydrogenase alone and in various combinations in identifying DMD carriers. We analyzed 127 serum samples from 63 normal female controls (20-40 years old) and 67 from 38 obligate DMD carriers. The best two tests to use in combination were creatine kinase and hemopexin, and these two, with lactate dehydrogenase, were the best three. t the 95% level (with 5% of controls misclassified), 54% of the carriers were identified by CK alone, whereas 88% were identified by means of the four tests. Although a small proportion of known carriers still cannot be identified, application of the four tests to a group of 45 possible carrier mothers of isolated cases of DMD resolves the population into fairly discrete "normal" and "abnormal" subgroups. Thus, if bias of selection can be eliminated, application of logistic discrimination may permit a direct estimate of the proportion of mothers of affected boys who are homozygous normal.

The effect of parental age on rate of mutation for Duchenne Muscular dystrophy

The effect of parental age on mutation rates at the Duchenne Muscular Dystrophy (DMD) locus was studied in 514 male probands who constitute two thirds of the known patients in Japan. We were unable to detect an effect of maternal age at birth of proband or maternal grandfather's age at birth of the mother of the proband on the rate of DMD mutations. The result supports an observation on the hemophilia gene.

Creatine kinase activity in the detection of carriers of Duchenne muscular dystrophy: comparison of two methods

Serum creatine kinase activity was estimated in 48 control women and 22 female carriers of Duchenne muscular dystrophy by two different methods. One method is based on the colorimetric determination of creatine liberated from creatine phosphate; the other, an N-acetyl cysteine activated UV system, was used in an automated mode. The two methods were equally efficient in carrier detection, and results were closely correlated over the range of values encountered in controls and carriers. Log creatine kinase values appeared to be normally distributed in controls, but the distribution in carriers appeared skewed towards its upper end. If both distributions are assumed to be Normal, the probability, together with its standard error, that a consultand is a carrier, can be calculated from her creatine kinase value, and if the latter is expressed in standard deviation units of the control log creatine kinase distribution, probability estimates can be compared between laboratories.

Prenatal diagnosis of Duchenne muscular dystrophy: failure of amniotic fluid and maternal serum N tau-methylhistidine analyses to detect affected fetuses

N tau-Methylhistidine (MH) and creatinine levels were determined in amniotic fluid and maternal serum from 81 women undergoing midtrimester amniocentesis for reasons other than the diagnosis of neuromuscular disease. Samples were also examined in three pregnancies with male fetuses who were subsequently found to have Duchenne muscular dystrophy (DMD). Between 16 and 20 weeks' gestation, amniotic fluid and maternal serum MH levels averaged 3.22 and 1.94 mumoles/L, respectively. No significant differences were found between the control and affected fetuses for MH and creatinine levels or for MH/creatinine ratios from amniotic fluid or maternal serum. Determination of amniotic fluid MH level thus has no apparent value in the prenatal diagnosis of DMD.

Serum creatine kinase in the detection of Duchenne muscular dystrophy carriers: effects of season and multiple testing

The usefulness of serum creatine kinase (CK) activity in the detection of Duchenne muscular dystrophy (DMD) carriers is dependent upon a reliable control distribution. In controls there is a small but reproducible seasonal variation in CK activity, with a statistically significant variation in the upper 95th percentile (78 IU/liter in May, 53 IU/liter in November, as compared with 67 IU/liter for the whole calendar year). Because CK values in DMD heterozygotes are higher in November than in May, the carrier detection rate may be highest in November. Failure to consider this seasonal variation in controls may cause misclassification of too many normal subjects. If tests are conducted throughout the year, however, the seasonal influence can be reduced by serial testing at intervals of several months. In this case, use of the highest of the results obtained in 3 tests compared with the normal range of single measurements misclassifies too many normal subjects. Use of the mean of 3 determinations provides more accurate classification.

Erythrocyte spectrin in Duchenne muscular dystrophy

The primary structure of erythrocyte spectrin bands I and II from controls and patients with Duchenne muscular dystrophy was compared by 2-dimensional peptide mapping. 125I-labelling was done either by the chloramine-T method or using the Bolton and Hunter reagent followed by treatment with trypsin or chymotrypsin, resulting in four different peptide maps from each band of spectrin. Although all the peptide maps of band I were considerably different to those of band II, there were no consistent differences in the maps of bands I and II from controls compared to the corresponding maps from patients with Duchenne muscular dystrophy.

Translocation (X;6) in a female with Duchenne muscular dystrophy: implications for the localisation of the DMD locus

A female with Duchenne muscular dystrophy who was a carrier of a balanced translocation t(X;6)(p21;q21) is reported. Four other previously described (X;A) translocations associated with DMD share with the present case a breakpoint at Xp21. The extremely low probability of five independent (X;A) translocations having a breakpoint at Xp21 points to a non-rand association of this site with the DMD phenotype. A DMD locus at Xp21 could be damaged by the translocation, giving rise to Duchenne muscular dystrophy. Alternatively, a pre-existing DMD gene could weaken the chromosome, favouring breaks at Xp21.

Activity of creatine kinase in sera from healthy women, carriers of Duchenne muscular dystrophy and cord blood, determined by the "European" recommended method with NAC-EDTA activation

Creatine kinase activity has been measured at 37 degrees C in sera from healthy women, carriers of Duchenne muscular dystrophy and cord blood, with activation by N-acetyl cysteine (NAC) and EDTA as recommended by several European committees on standardisation. The upper limit of the reference range for healty women was found to be 170 U/l. The distributions of creatine kinase activities in healthy and carrier women have been used to calculate probability of carrier status as a function of creatine kinase activity. Although the range of creatine kinase activities in normal cord blood is wide, the data provide a basis for interpretation when Duchenne muscular dystrophy is suspected.

Serum myoglobin in muscular dystrophy and carrier detection

Serum myoglobin was measured by radioimmunoassay in 143 patients with various muscle diseases including 55 boys with Duchenne dystrophy, 56 carriers of the Duchenne dystrophy gene, 8 carriers of the Becker dystrophy gene, 60 first-degree relatives of patients with sporadic (non-genetically transmitted) muscle diseases and 85 normal controls. A significant difference (P less than 0.001) was found between the serum myoglobin levels in normal control men (x = 31.7 range 10-70 microgram/l) and those in women (x = 17.2 range 4-27 microgram/l) but no difference was found between the controls and relatives of patients with muscle disease. Up to the age of 60 years, no correlation was found between age and serum myoglobin levels in controls. However, levels in boys with Duchenne dystrophy were found to increase slightly up to the age of 10 years and to decrease thereafter. No correlation was found between serum myoglobin and creatine kinase activity in these boys but in Duchenne carriers correlation was close (P less than 0.001). Eighteen of 23 definite and 13 of 33 possible carriers of Duchenne dystrophy had myoglobin concentrations above the equivalent normal range. Of those carriers with elevated myoglobin levels, 7 definite and 4 possible carriers had normal serum creatine kinase activity. This was equivalent to an improvement in "detection" of 31% and 12% in these groups of carriers. Of the 8 Becker dystrophy carriers, 6 had elevated myoglobin but all had normal creatine kinase levels. It appears that measurement of serum myoglobin as well as creatine kinase activity may be of great benefit to carrier detection programmers, but the need to establish accurately the extent of normal variation in women is emphasized.

Calf hypertrophy and asymmetry in female carriers of X-linked Duchenne muscular dystrophy: an over-diagnosed clinical manifestation

The height, weight and calf sizes of 19 carriers of X-linked Duchenne muscular dystrophy were compared with 32 normal female controls of comparable age. Whereas the regression of the sum of right and left calf sizes on weight was highly significant in both groups, the difference between right and left calf size showed no significant association with weight, height or age. There was no significant difference between carriers and controls in the sum of calf sizes either before or after correction for weight by Analysis of Covariance and no significant difference between the two groups in the degree of asymmetry of right and left calf size.