The classic disease is infantile in onset with hypotonia, titubation, weakness, stridor, respiratory problems, and even seizures often noted in the first weeks of life. Ataxia, spasticity and cognitive delay are soon apparent. Infants affected early and severely may never achieve normal motor or mental milestones whereas those less severely affected may at some point ambulate and acquire some language skills. However, acquired skills may be lost by adolescence. Survival to the sixth decade of life is common but those with the most severe form of disease may not live beyond the second decade.
This is an X-linked recessive disorder in which only males have the complete syndrome. However, multiple carrier females have been studied and many have subtle evidence of disease mainly in gait and motor control.