Hartnup was first described in four of the eight family members with aminoaciduria, a skin rash resembling pellagra and cerebellar ataxia by Baron and his colleagues.
The condition was discovered in a boy in Hartnup family who present with photosensitive rash, ataxia, hand tremors, and gait disturbances. The causative gene, SLC6A19, is located on a locus on short arm of chromosome 5 (band 5p15.33) which encodes a transporter.
On investigation of further family members, his other three siblings were also found to have the same syndrome with varying clinical symptoms.
The disease is due to a deficit in the intestines and kidneys, making it difficult for the body to break down and absorb dietary tryptophan (an essential amino acid that is utilized to synthesize niacin).
The National Organization for Rare Disorders reports that Hartnup disease is estimated to affect about one in 30,000 people in the United States. Symptoms normally start to appear in infancy or the first few years of life.
Discovery of Hartnup disease
