Hartnup disease

L-tryptophan-skeletal

Hartnup disease is a rare autosomal recessive metabolic disorder that affects the absorption of certain amino acids, particularly tryptophan, in the intestines and kidneys. This condition is named after the Hartnup family, in which the disease was first identified.

Pathophysiology

Hartnup disease is caused by mutations in the SLC6A19 gene, which encodes a transporter protein responsible for the absorption of neutral amino acids in the renal tubules and intestinal epithelium. The defective transporter leads to increased excretion of these amino acids in the urine and decreased absorption from the diet, resulting in a deficiency of essential amino acids.

Symptoms

The symptoms of Hartnup disease can vary widely among affected individuals. Common symptoms include:

• Photosensitivity rash
• Ataxia
• Psychiatric symptoms such as depression and anxiety
• Pellagra-like symptoms due to tryptophan deficiency, which can lead to a deficiency in niacin (vitamin B3)

Diagnosis

Diagnosis of Hartnup disease is typically based on clinical symptoms and confirmed by laboratory tests showing increased levels of neutral amino acids in the urine. Genetic testing can identify mutations in the SLC6A19 gene.

Treatment

Treatment for Hartnup disease focuses on managing symptoms and preventing complications. This may include:

• High-protein diet to ensure adequate intake of essential amino acids
• Niacin supplements to prevent pellagra-like symptoms
• Avoidance of sun exposure to prevent photosensitivity rashes

Prognosis

With appropriate management, individuals with Hartnup disease can lead normal lives. However, untreated or poorly managed cases can result in significant complications, particularly related to the skin and nervous system.

See also

• Amino acid metabolism
• Autosomal recessive disorder
• Pellagra
• SLC6A19