Unraveling the mysteries of Duchenne and Becker muscular dystrophy.

Through a process that has come to be known as reverse genetics, the gene and gene product involved in Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) have been identified. The DMD/BMD gene is over 2 million base pairs in size and over 50% of DMD/BMD patients harbor submicroscopic deletions for portions of the gene. The gene product, named dystrophin, is 400 Kd in size. Dystrophin is present in skeletal, cardiac, and smooth muscles, as well as brain. The protein is absent or altered in DMD/BMD patient muscle. The normal function of dystrophin and the reasons why its alteration results in the DMD/BMD phenotypes are presently unknown. The discoveries to date, however, provide a starting point for investigating the fundamental pathogenetic mechanisms involved in DMD/BMD.

Scapuloperoneal neuropathy: a distinct clinicopathologic entity.

Peripheral neuropathy as a cause for the scapuloperoneal syndrome continues to be controversial. This report provides further evidence in support of a scapuloperoneal neuropathy as a separate nosologic entity. Three men had a slowly progressive disorder of 5-17 years duration with prominent weakness and atrophy of scapular stabilizer, shoulder girdle and distal lower extremity muscles accompanied by a distal pan-modality sensory loss. Electrodiagnostic studies and sural nerve biopsies indicated a primary axonal neuropathy with secondary demyelination and remyelination.

Recent advances in Duchenne and Becker muscular dystrophy.

The recent identification of the gene and gene product altered in Duchenne and Becker dystrophy has opened up new and exciting avenues to an understanding of these diseases. This article presents the clinical features, pathology, genetics, and management of Duchenne and Becker muscular dystrophy. These issues are discussed in light of the rapidly accumulating knowledge concerning the molecular basis for the two disorders.

Genetic heterogeneity in Duchenne dystrophy.

We evaluated 173 patients in the Clinical Investigation of Duchenne Dystrophy study to determine if patients from the same kindred were more alike clinically than patients within the study population as a whole. A high intrafamilial correlation was noted for age-adjusted muscle strength scores. While noninherited factors could, in part, explain the results, it seems likely that genetic heterogeneity may contribute to the observed similarity within Duchenne dystrophy kindreds.

Carrier assessment for mothers and sisters of isolated Duchenne dystrophy cases: the importance of serum enzyme determinations.

DNA studies (restriction fragment length polymorphism linkage analysis and deletion analysis with pERT87) and serum creatine kinase/pyruvate kinase (CK/PK) measurements were done to determine the carrier status of 59 mothers and sisters of isolated Duchenne dystrophy (DD) cases. The results of DNA studies modified the carrier risks for 34 of the 59 (58%), but the derived risks often did not differ importantly from risks calculated by conventional methods. Elevated CK/PK provided strong evidence of the carrier state for 24 of the 59 (41%), and CK/PK frequently provided data unavailable through DNA studies. Serum enzyme determinations remain an important means of evaluating DD carrier suspects and are especially valuable in isolated-case families. Enzyme testing should be combined with DNA studies to achieve the best estimate of carrier risk.

Three cases of amyotrophic lateral sclerosis in a common occupational environment.

Three unrelated school teachers taught in the same school classroom for 2-5 years and subsequently developed amyotrophic lateral sclerosis (ALS) over an 18-year period. This clustering was not accompanied by an increased death rate for ALS in the county where the teachers lived and worked. Statistical analysis revealed that ALS as the cause of death for three teachers from the same school would be highly improbable as a random event. These findings suggest that the patient's shared school environment may have been a source of exposure to an agent pathogenetically significant in the development of their disease.

Monozygotic female twin carriers discordant for the clinical manifestations of Duchenne muscular dystrophy.

We studied twin sisters, in their sixth decade, who were obligate carriers of Duchenne dystrophy. One had a slowly progressing limb-girdle myopathy since her mid-20s. The other sister showed no evidence of neuromuscular disease by history or on physical examination but had high serum CK values and degeneration and regeneration of fibers in a muscle biopsy. Otherwise, they were phenotypically identical, karyotypically normal females with cytogenetically normal X-chromosomes. Based on red cell and HLA loci antigen determinations, there was a 99.2% probability that they were monozygotic. The mutant gene segregating in the family is probably linked to the Xp21 DNA marker pERT87.

Use of serum creatine kinase, pyruvate kinase, and genetic linkage for carrier detection in Duchenne and Becker dystrophy.

Carrier detection in Duchenne dystrophy (DD) and Becker dystrophy (BD) can be achieved with DNA probes that recognize restriction fragment length polymorphisms (RFLPs). In 22 families, we found that 16 of 23 females at risk for being DD or BD carriers could be provided with more definitive indications of carrier status beyond the use of creatine kinase/pyruvate kinase and pedigree analysis. RFLP analysis was not possible for six individuals despite potentially informative probes, because family members critical to the analysis were unavailable. In only one instance were all eight probes uninformative.

Status epilepticus after baclofen withdrawal.

Baclofen is widely used in the treatment of spasticity of spinal origin. It is relatively free of side effects or toxic actions on the nervous system or other organs. Agitation, personality change, and auditory and visual hallucinations have been described following its abrupt withdrawal. One patient with generalized seizures and one with complex partial seizures after baclofen withdrawal have been reported. This paper presents a patient who developed status epilepticus after baclofen withdrawal, and who sustained hypoxic cerebral injury. This observation further emphasizes the possibility of infrequent complications of baclofen therapy, and the advisability of gradual changes in baclofen dosage.

Myoclonus induced by metoclopramide therapy.

Metoclopramide hydrochloride is increasingly used as an antiemetic agent. Clinical and experimental studies have demonstrated dopamine antagonism, and extrapyramidal side effects have been reported in patients given the drug for gastrointestinal disorders. Multifocal myoclonic jerking developed in our patient after he received metoclopramide therapy for gastroparesis due to renal failure. He had had no previous neurologic symptoms, and no evidence of CNS abnormality was found; the myoclonic jerking subsided when metoclopramide therapy was discontinued. Multifocal myoclonus must be differentiated from seizure activity in patients with renal failure and other metabolic encephalopathies. Metoclopramide clearance is reduced in renal failure, and myoclonus or other neurologic complications may be precipitated in such patients by usual doses of this drug.