Mevalonate kinase (MK) is the first enzyme after 3-hydroxy-3-methylglutaryl-CoA reductase in the biosynthesis of cholesterol and nonsterol isoprenes. In 1986, Hoffmann reported a patient with mevalonic aciduria due to mevalonate kinase deficiency, failure to thrive, severe psychomotor retardation, dysmorphic features and cataract. Few other patients have subsequently been described; they have variable degree of neurological impairment, but in all recurrent crisis of high fever, lymphoadenomegaly, hepatosplenomegaly and diarrhoea are reported (Hoffmann et al 1993).

Recently another group of patient with mevalonate kinase deficiency has been identified: they have a disease known as hyperimmunoglobulinaemia D and periodic fever (HIDS; McKusick 260920)(Drenth et al., 1999; Houten et al., 1999). HIDS is characterized by recurrent febrile attacks usually with very early onset (under 1 year), associated with abdominal pain, diarrhoea, arthralgias, lymphoadenopathy and splenomegaly. Neurological and physical development are normal. Persistently elevated serum IgD is reprted as a specific marker.