Mutation in hanup disease:
**Core Concept**
Hanup disease, also known as Hartnup disease, is a rare genetic disorder affecting the metabolism of amino acids. It is caused by mutations in the SLC6A19 gene, which encodes the neutral amino acid transporter 1 (NAAT1). This transporter plays a crucial role in the reabsorption of neutral amino acids in the kidneys and intestines.
**Why the Correct Answer is Right**
The mutation in the SLC6A19 gene leads to impaired function of the NAAT1 transporter, resulting in the inability to reabsorb neutral amino acids properly. This causes an excessive excretion of these amino acids in the urine, leading to a range of clinical manifestations, including pellagra-like symptoms, ataxia, and psychiatric disturbances. The impaired amino acid transport also affects the levels of serotonin and other neurotransmitters, contributing to the neurological symptoms.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the gene responsible for Hanup disease. While the gene is crucial for understanding the disease, the question asks about the mutation itself, not the underlying genetic cause.
**Option B:** This option is incorrect because it refers to a different disease altogether. While both diseases involve genetic mutations, they are distinct conditions with different underlying mechanisms and clinical presentations.
**Option C:** This option is incorrect because it mentions a gene involved in a different metabolic pathway. While the gene is involved in amino acid transport, it is not the gene responsible for Hanup disease.
**Clinical Pearl / High-Yield Fact**
Hanup disease is a rare genetic disorder that highlights the importance of amino acid transport in maintaining proper neurotransmitter levels and preventing neurological symptoms. It also underscores the need for careful consideration of genetic factors in patients presenting with atypical symptoms.
**Correct Answer:** SLC6A19