ABSTRACT
This chapter discusses non-amyotrophic lateral sclerosis (ALS) forms of motor neuron degeneration that have a genetic basis. The conditions covered include the spinal muscular atrophies (SMAs), the hereditary motor neuropathies (HMNs), Kennedy’s disease and the hereditary spastic paraplegias (HSPs). SMA was first described independently by Werdnig and Hoffman in 1891. The term SMA encompasses a group of genetically determined pure lower motor neuron disorders. Nascent pre-mRNA transcripts are processed in the nucleus to produce mature mRNA by removal of introns. SMA with arthrogryposis and bone fractures is characterized by a pattern of weakness indistinguishable from SMA type 1, and congenital long-bone fractures. Distal muscle wasting in a scapuloperoneal distribution may be myopathic or neurogenic in origin. Patients frequently have mild androgen insensitivity, causing gynecomastia, testicular atrophy, oligospermia and erectile dysfunction. Clinical features of androgen insensitivity suggested a defect in androgen-reoeptor function.
