Syndrome with characteristics of intellectual deficit, early-onset hypotonia, ataxia, delayed motor development, hearing impairment and loss of vision due to optic atrophy. Other manifestations included floppiness, susceptibility to infections and later flaccid tetraplegia and areflexia. It is caused by missense mutations in the phosphoribosyl pyrophosphate synthetase 1 gene (PRPS1) localized to Xq22.1-q24, leading to impaired purine biosynthesis. Transmitted as an X-linked recessive trait. The disease has a fatal course during childhood (the majority of patients die before the age of 5 years) due to the high susceptibility of the patients to infections, especially of the upper respiratory tract.