The 4-hydroxybutyricaciduria deficiency is a metabolic disorder with a neurological presentation ranging from mild to severe. It is a rare disease with around 350 cases reported. The most frequent symptoms are psychomotor retardation, delayed speech development, hypotonia and ataxia. Transmission is autosomal recessive and mutations in the SSADH (Succinic Semialdehyde Dehydrogenase NAD(+)-Dependant) gene, located on chromosome 6p22, have been reported. The key biochemical feature is an accumulation of gamma-hydroxybutyrate in urine, plasma and cerebro-spinal fluid. There is no efficient treatment available.