A 2-year old male child presents with pellagra like lesions with passage of amino acids in urine. In the family, out of 4 siblings, two are having similar symptoms with two normal siblings and parents are not affected. Most likely diagnosis is:
**Core Concept**
Pellagra-like lesions and the passage of amino acids in urine suggest a disorder of tryptophan metabolism. Tryptophan is an essential amino acid that serves as a precursor for the synthesis of niacin (vitamin B3) and serotonin. A defect in the metabolism of tryptophan can lead to the accumulation of toxic intermediates, causing a range of clinical symptoms.
**Why the Correct Answer is Right**
The correct diagnosis is Hartnup disease, a rare autosomal recessive disorder caused by mutations in the SLC6A19 gene. This gene encodes a neutral amino acid transporter responsible for the reabsorption of tryptophan and other neutral amino acids in the kidneys and intestines. In Hartnup disease, the impaired reabsorption of tryptophan leads to its excessive excretion in the urine, causing a range of clinical symptoms, including pellagra-like lesions, due to the decreased availability of niacin. The passage of amino acids in the urine is a hallmark of this disease.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the clinical presentation described in the question. While there are several disorders that cause amino aciduria, Hartnup disease is the most likely diagnosis given the combination of pellagra-like lesions and passage of amino acids in urine.
**Option B:** This option is incorrect because it does not accurately describe the inheritance pattern of Hartnup disease. Hartnup disease is an autosomal recessive disorder, meaning that affected individuals are homozygous for the mutated gene.
**Option C:** This option is incorrect because it is not a known disorder that causes pellagra-like lesions and passage of amino acids in urine.
**Clinical Pearl / High-Yield Fact**
Hartnup disease is a rare disorder that highlights the importance of tryptophan metabolism in human health. The impaired reabsorption of tryptophan in Hartnup disease can lead to a range of clinical symptoms, including pellagra-like lesions, due to the decreased availability of niacin. This disorder is a classic example of how a defect in a single enzyme or transporter can have far-reaching consequences for human health.
**Correct Answer:** C.