You will be shown biomedical passages and your task is to the answer the provided question. Provide a concise and accurate response and do not include any additional text in the response other than the answer.

Question: What gene is mutated in Huntington's Disease patients?

Context: Huntington's disease (HD) is a fully penetrant neurodegenerative disease caused by a dominantly inherited CAG trinucleotide repeat expansion in the huntingtin gene on chromosome 4
Huntington's disease (HD) is caused by a CAG repeat expansion that encodes a polyglutamine (polyQ) expansion in the HD disease protein, huntingtin (HTT). PolyQ expansion promotes misfolding and aggregation of mutant HTT (mHTT) within neurons.
Huntington's disease (HD) is a neurodegenerative disorder that is caused by abnormal expansion of CAG repeats in the HTT gene.
Two decades ago, researchers identified that a CAG expansion mutation in the huntingtin (HTT) gene was involved in the pathogenesis of Huntington's disease (HD).
However, since the identification of the HTT gene, there has been no advance in the development of therapeutic strategies to prevent or reduce the progression of HD
Mutations in the HTT gene , consisting of expansion of CAG triplets , cause the Huntington 's disease ( HD) , one of the major neurodegenerative disorders .
Huntington 's disease is a neurodegenerative disorder of the brain that is caused by the mutation of the gene which produces a protein called huntingtin ( htt) .
Huntington 's disease ( HD ) is an autosomal dominant neurodegenerative disorder of the central nervous system ( CNS ) that is defined by a CAG expansion in exon 1 of the huntingtin gene leading to the production of mutant huntingtin ( mHtt) .
A mutation in the huntingtin ( Htt ) gene produces mutant Htt and Huntington 's disease ( HD) , a neurodegenerative disorder .
Huntington 's disease ( HD ) is a devastating neurodegenerative disorder that occurs in patients with a mutation in the huntingtin or IT15 gene.
Huntington's disease is an inherited disorder caused by expanded stretch of consecutive trinucleotides (cytosine-adenosine-guanine, CAG) within the first exon of the huntingtin (HTT) gene on chromosome 4 (p16.3).
Huntington's disease is an inherited disorder caused by expansion of a CAG trinucleotide repeat in the IT15 gene, which leads to expansion of a polyglutamine tract within the protein called huntingtin.
Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by high instability and extension of CAG sequences within the coding region of IT15 gene.
Huntington's disorder (HD), caused by mutations of the IT-15 gene, is an autosomal genetic disease that causes the breakdown of the nerve cells in the brain.
Huntington's disease is caused by an expanded trinucleotide CAG repeat in the HD gene on chromosome 4.
Positional cloning has shown that the Huntington disease (HD) mutation is an expanded trinucleotide repeat in the IT15 gene.
HTT gene encoding the protein huntingtin