Capping of lymphocytes for carrier detection in Duchenne muscular dystrophy: technical problems and a review of the literature

Lymphocytic beta-adrenergic receptors in X-linked muscular dystrophy

Lymphocytic beta-adrenoceptor levels, receptor binding affinity, lymphocytic basal and isoproterenol-stimulated cyclic AMP (cAMP) production and plasma catecholamine levels were studied in 49 patients with neuromuscular diseases and in 10 healthy subjects. Patients with X-linked muscular dystrophy (Duchenne, 13 patients; Becker, 4 patients) showed a significant reduction in lymphocytic beta-adrenoceptor densities (35.9 +/- 2.2 fmol/mg protein vs. 49.6 +/- 3.6 fmol/mg, controls; P less than 0.02), whereas the receptor levels for the patients with spinal muscular atrophy (15), polymyositis (10) and for Duchenne carriers (7) did not differ significantly from the corresponding levels for the control subjects. The reduction in the beta-adrenoceptor density was not correlated with the physical disability of the patients. Lymphocytic beta-adrenoceptor affinity (KD) and basal and isoproterenol-stimulated cAMP levels were all comparable to control subjects' values. Catecholamine levels showed mild inconsistent elevations in various patient groups. The results suggest that reduction in cellular beta-adrenoceptors is characteristic of X-linked muscular dystrophies. Its relationship to the basic gene defect is unknown.

Systemic membrane defect and the inhibition of lymphocyte capping in Duchenne muscular dystrophy

Eight reversible inhibitors were used to study decreases in lymphocyte capping in patients with Duchenne Muscular Dystrophy (DMD) when compared to controls. The inhibitors included hydrocortisone, chlorpromazine, calcium ionophore, Cytochalasin D, propranolol, dibucaine, fluoride and azide. All of these inhibitors disrupt cap formation. Mononuclear leukocytes from DMD patients and controls were isolated from whole blood, incubated with fluorescein-conjugated polyvalent antisera and inhibitor, induced to form caps, and the caps counted using a fluorescent microscope. Cell viabilities and morphology were assessed. After removal of inhibitor, the cells were recounted. All of the inhibitors significantly lowered capping in controls (p less than 0.001), but this effect was seen with only four out of the eight inhibitors in DMD patients. Dibucaine and azide were less inhibitory in patients (p less than 0.005, p greater than 0.05, and p greater than 0.05 respectively) while capping in patients was not inhibited by fluoride and hydrocortisone (p greater than 0.5). The lack of hydrocortisone inhibition suggests that the differences in capping between DMD patients and controls may lie within the membrane itself, rather than its associated components (i.e. cytoskeletal network), and that the defect occurs toward the beginning of the capping sequence.

Carrier detection in Duchenne muscular dystrophy: a review of current issues and approaches

The clinical chemistry laboratory has traditionally played a passive role in the application of technology to diagnostic interpretation. Recent developments offer the clinical laboratorian a renewed potential to enter the patient care arena as a consultant. Our lack of understanding of the disease processes in the muscular dystrophies places emphasis on prevention through carrier detection. This review summarizes the clinical progress of the disease, our present understanding of the genetics that control the mode of inheritance of the disease, and the analytical approaches to carrier detection, including their advantages and limitations. Recent advances allow the examination of the genetic material itself instead of concentrating on the phenotypic expression of biochemical abnormalities.

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 genetic status of mothers of isolated cases of Duchenne muscular dystrophy

Classical genetic theory, based on assumed equal mutation rates in males and females, predicts that one-third of all cases of Duchenne muscular dystrophy (DMD) in a generation are born as new mutants to non-carrier mothers. Furthermore, less than half the mothers of apparently isolated cases appear to be carriers on the basis of raised serum creatine kinase levels. We have analysed the pedigrees of 61 families of DMD boys seen in the Duke Neuromuscular Research Clinic and 45 DMD families followed at the University of Virginia. The frequency of affected boys among the next born male sibs of 37 initially isolated DMD cases in two clinic populations was significantly greater than predicted by Haldane's theory (p = 0.029) and the estimated proportion of new mutant cases in the combined clinic population of 106 families was 0.127 (SE 0.111). The absence of affected males in earlier generations in families of isolated cases may be explained in part by a high ratio of male to female stillbirths and infant deaths, which was more than three times that of the normal population in this study. These data suggest that new mutant cases are less common than expected and current predictions may underestimate genetic risks in mothers of isolated cases.

An evaluation of lymphocyte capping in Duchenne muscular dystrophy

There have been conflicting reports of lymphocyte capping abnormalities in Duchenne muscular dystrophy (DMD). We have evaluated the original method described by Verrill et al. in a "blind" study of 24 Duchenne muscular dystrophy boys and paired age-matched control boys. We found no differences in capping between the two groups but control boys had decreased capping compared to a group of normal adult males and females. It is concluded that the initial reports of decreased capping in DMD may have been due to differences in age between the test and control group.

Lymphocyte capping in muscular dystrophies

Since reports of lymphocyte capping in muscular dystrophies of various authors revealed controversial results, we investigated 47 patients and carriers with Duchenne or Becker-Kiener muscular dystrophy according to different methods. There was no significant reduction of cap formation compared to 64 healthy controls, both groups showing a mean of about 75% caps. Reduced numbers of caps, however, could be demonstrated in three otherwise healthy probands aged 70 years or more, two patients under interferon treatment, four patients under high dose methotrexate therapy as well as one patient with untreated chronic myeloic leukemia. Thus lymphocyte capping in our experience is far from being a valid method for carrier detection or prenatal diagnosis of muscular dystrophies.