The nosology of the spinal muscular atrophies

A family of juvenile proximal spinal muscular atrophy with dominant inheritance

A family with juvenile proximal spinal muscular atrophy with dominant inheritance and complete penetrance is reported. The disease occurred in three generations and showed high variations in the age of onset and progression among the affected members. A characteristic feature was the constant involvement of facial nuclei.

Cerebellar hypoplasia in Werdnig-Hoffmann disease

The case of an infant with Werding-Hoffmann disease, who died at the age of 4 1/2 days, is reported. At autopsy there was severe cerebellar hypoplasia, associated with degenerative changes in the brain-stem nuclei. This case supports the concept that cerebellar hypoplasia may develop as a manifestation of the neuronal abiotrophy of Werdnig-Hoffmann disease. A similarity has been noted between the cerebellar lesion found in the child reported here and that produced by viral infection in experimental animals.

Ultrastructural aspects of muscle and nerve in Werdnig-Hoffmann disease

The authors describe in biopsies from 6 cases of Werdnig-Hoffmann disease, including 2 of the more benign type, the ultrastructural typical aspects of denervation. They compare their findings with those of other workers. The striking points are the great variation in the diameter of the muscle fibres and the myofibrils, the disorganisation of the myofibrils, the sarcomeres and the filaments, with persistance of the relations between thick and thin filaments at various levels, the modifications of the Z-band and the triads in chains. The folds and the basement membrane are examined. Centrioles are present in a muscle fibre and in a satellite. Glycogen is very abundant. The nerves seem normal but some Schwann cells contain pi granules which are not observed usually at the age of the patient. The end plates and a muscle spindle are normal.

A neurogenic component in muscular dystrophy

Evidence for a neurogenic component in mouse and human muscular dystrophy is briefly reviewed. Such evidence comes from certain clinical observations, electrophysiological studies, muscle pathology, nervous system pathology, transplantation experiments in animals, and tissue culture studies. The evidence is at present rather conflicting though the results of recent tissue culture experiments are more convincing. If there is a neurogenic component in dystrophy then the basic defect may have to be sought in the central nervous system rather than in the muscle itself. It is argued, however, that a neurogenic component in dystrophy cannot be simply a defect in the anterior horn cells of the spinal cord since the clinical features and the laboratory and pathological findings are quite different from those in spinal muscular atrophy.

Chronic generalized spinal muscular atrophy of infancy and childhood. Arrested Werdnig-Hoffman disease

Recent studies have shown that the acute fatal form of infantile spinal muscular atrophy (acute Werdnig-Hoffmann disease or spinal muscular atrophy Type I) is a distinct genetic and clinical entity. This has prompted clinical re-examination of the disease known as `arrested Werdnig-Hoffmann disease' which hitherto was thought to be a spectrum variant of the acute fatal form. A total of 18 such patients with the chronic generalized form of spinal muscular atrophy has been known to The Hospital for Sick Children over the past 10 years. Patients with this characteristic clinical syndrome comprise approximately one-fifth of children with chronic spinal muscular atrophy. Clinically, no patient was even able to crawl normally or progress further with motor milestones. Median age of clinical onset is 6 months of age, and life expectancy ranges from 2 years to the third decade. Inevitable spinal and joint deformities occur by the second decade of life. Management should be based on vigorous antibiotic therapy, orthopaedic and neurological surveillance, and a carefully planned educational programme aimed at realistic employment in late adolescence.

The gene frequency of acute Werdnig-Hoffmann disease (SMA type 1). A total population survey in North-East England

A retrospective total population study of acute Werdnig-Hoffmann disease (spinal muscular atrophy type 1) has been undertaken in three counties of North-East England (Northumberland, Newcastle upon Tyne, and Durham). The gene frequency for the disease is q=0·00625 with a carrier frequency for this part of the English population of 1 in 80. The data suggest that there may be differences in gene frequency within the region sampled, a finding in keeping with other investigations of variations in gene frequency in this region. The suggestion that this disease is the second most common fatal autosomal recessive disease of childhood in Britain is confirmed. An hypothesis of heterozygote advantage due to relative resistance to epidemic poliomyelitis is presented to account for the high gene frequency observed.

Acute Werdnig-Hoffmann disease: acute infantile spinal muscular atrophy

76 cases of acute Werdnig-Hoffmann disease (acute infantile spinal muscular atrophy) have been reviewed. The cases comprise an unselected consecutive series in which rigid diagnostic criteria have been applied. The natural history of the disease has been investigated. In at least one-third of cases the disease is manifest before or at delivery. All cases have shown delayed milestones by 5 months of age: 95% are dead by 18 months. Cumulative frequency curves for age at onset and age at death figures are presented for use both as prognostic guidelines and as aids in the management of sibs of index cases. Diagnosis, management, and genetic implications are discussed.

Electromyographic studies in parents of children with spinal muscular atrophy

Electromyographic studies have been carried out on the quadriceps and deltoid muscles of a number of healthy parents of children with infantile spinal muscular atrophy (types I and II) and the results compared with those obtained in healthy controls of the same sex. The results indicated an increase in mean amplitude of action potentials in quadriceps and deltoid muscles in both fathers and mothers (statistically significant in the quadriceps in the latter) of children with type I spinal muscular atrophy (Werdnig-Hoffmann disease). Increase in the mean amplitude in the quadriceps and deltoid muscles in mothers of children with type II spinal muscular atrophy and the mean duration of action potentials in the quadriceps muscle in mothers of children with type I and type II spinal muscular atrophy were also observed, but the differences from controls were not significant.