Question: What is (are) Hartnup disease ?
Answer: Hartnup disease is a metabolic disorder characterized by abnormal transport of certain amino acids in the kidney and gastrointestinal system. It is a type of aminoaciduria. The condition may be diagnosed based on the results of newborn screening tests. Most people with the condition have no symptoms (asymptomatic). For those who do show symptoms, the onset of the disease is usually between the ages of 3 and 9; occasionally the disease may present in adulthood. Mental development is usually normal, though a few cases with intellectual impairment have been reported. The signs and symptoms of Hartnup disease incude skin photosensitivity, neurologic findings, psychiatric symptoms, and ocular (eye) findings. Hartnup disease is caused by mutations in the SLC6A19 gene and is inherited in an autosomal recessive manner.[1][2] People with Hartnup disease may benefit from a high-protein diet, protection from sunlight, vitamin supplementation, and avoidance of certain drugs/medications. In some cases, treatment with nicotinamide supplements and tryptophan ethyl ester may be indicated.
Source: GARD

Question: What are the symptoms of Hartnup disease ?
Answer: What are the signs and symptoms of Hartnup disease? The signs and symptoms of Hartnup disease may vary and include the following: Skin findings: sensitivity to sunlight Neurologic symptoms: ataxia, spasticity, headaches,and hypotonia Psychiatric symptoms: anxiety, emotional instability, mood changes Ocular findings: double vision, nystagmus, strabismus, photophobia Symptoms may be triggered by sunlight exposure, fever, drugs, and emotional or physical stress. The episodes of skin and neurologic findings may last for 1-4 weeks before spontaneous remission occurs. The Human Phenotype Ontology provides the following list of signs and symptoms for Hartnup disease. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Cutaneous photosensitivity 90% EEG abnormality 90% Hallucinations 90% Hyperreflexia 90% Incoordination 90% Migraine 90% Muscular hypotonia 90% Malabsorption 50% Nystagmus 50% Photophobia 50% Short stature 50% Skin rash 50% Strabismus 50% Abnormal blistering of the skin 7.5% Cognitive impairment 7.5% Encephalitis 7.5% Gingivitis 7.5% Glossitis 7.5% Hypopigmented skin patches 7.5% Irregular hyperpigmentation 7.5% Seizures 7.5% Autosomal recessive inheritance - Emotional lability - Episodic ataxia - Hypertonia - Neutral hyperaminoaciduria - Psychosis - The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.
Source: GARD