A study of environmental factors in relation to fatal infantile spinal muscular atrophy (SMA type I). An analysis of birth order and parental age effects, social class, seasonal influence, and clustering in time and place

A novel behavioral method to detect motoneuron disease in Wobbler mice aged three to seven days old

The Wobbler mouse possesses an inherited autosomal recessive form of motoneuron disease. The most characteristic abnormality is the degeneration of motoneurons, mostly in the cervical spinal cord, and in the brain stem cranial motor nuclei. The underlying pathology shows up as symptoms that are only detectable confidently around the time of weaning (age 3 weeks). We now report a new method designed to identify presymptomatic Wobbler mice by behavioral and statistical approaches. We measured body weight, righting reflex (RR) and gender to examine whether these parameters have an impact on the status of the disease before age 3 weeks. Using a total of 341 NFR/wr strain pups, we found a strong association between RR and the Wobbler disease status (p<0.0001) between postnatal days 3 to 7, and achieved greater than 97% correct classification of Wobblers. Therefore the measurement of RR allows the early detection of the affected Wobbler (wr/wr) mice with a minimum of error. This method has been used in our laboratory for immunocytochemical studies that show the early sprouting of immunoreactive serotonin and peptidergic fibers in the cervical spinal ventral horn by postnatal days 7 and 12 respectively. The early detection of Wobbler mice thus facilitates significant new understanding regarding the pathogenesis of motoneuron disease. We can now examine potentially therapeutic approaches which may be more effective than when administered in the symptomatic weanlings (work in progress).

Classification of spinal muscular atrophies

Clinical heterogeneity within the spinal muscular atrophies (SMA) has long been a source of confusion for questions of prognosis and genetic counselling. Comprehensive clinical and genetic analyses of 240 consecutive index cases from two English centres (The English SMA Study) have enabled some nosological questions to be resolved. The different SMA syndromes can be discriminated by (a) age at the first clinical signs of the disease, (b) pattern of muscle involvement, (c) age at death of other patients within an affected kindred, and (d) genetic evidence. Seven different SMA syndromes can be defined clinically and genetically; thirteen mutant genes are incriminated. Prevalence and incidence figures are presented. SMA type I (Werdnig-Hoffman disease) and chronic childhood SMA together comprise 74% of all SMA cases. The classification of the spinal muscular atrophies presented also provides the differential diagnosis for newly presenting cases.