An unusual disorder, inherited in autosomal recessive manner, in which the body does not process and absorb adequate amounts of some amino acids (chemicals that make up proteins), especially tryptophan.
A lack of tryptophan can result in episodes of various symptoms, especially cerebellar ataxia (a badly co-ordinated, unsteady gait); symptoms like to those of pellagra: a scaly, red rash on skin exposed to the sun; depression and thought disorders. There can also be diarrhoea and headaches. Symptoms can be brought on by infections, exposure to sunlight, or stress, and last for up to four weeks. Flare-ups are usually followed by lengthy periods of remission.
The diagnosis can be made by testing the urine for unusually levels of amino acids. Treatment with nicotinic acid and a high-protein diet usually offers a good prognosis. The number of attacks often decreases with increasing age.