Symptoms and signs are due to niacinamide deficiency and resemble those of pellagra, particularly the rash on parts of the body exposed to the sun. Neurologic manifestations include cerebellar ataxia and psychologic abnormalities. Mental retardation, short stature, headache, and collapsing or fainting are common. Even though the disorder is present from birth, symptoms may present in infancy, childhood, or early adulthood. Symptoms may be precipitated by sunlight, fever, drugs, or other stresses.
Diagnosis is made by demonstrating the characteristic amino acid excretion pattern in the urine.
Indoles and other tryptophan degradation products in the urine provide supplementary evidence of the disease. The prognosis is good, and the frequency of attacks usually diminishes with age. An autosomal recessive benign defect in the renal tubular resorption of imino acids and glycine. Plasma levels of amino acids are normal. Intestinal absorption of proline may be impaired.