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Huntington’s Disease (HD) is a neurodegenerative disease which is progressive and produced by 36 or more repetitions of a specific triplet which is CAG. These repetitions are capable to encode a polyglutamate sequence. This abnormal sequence is produced by the alteration of huntingtin gene (HTT) which is found on the chromosome 4. HD is easily transmitted from sick parents to children, it means that is an autosomal dominant condition. For the following reason, this condition has 50% of probability to transmit the abnormal gene1. The symptoms of HD are manifested in the patients depending on their age because most cases, the appearance of symptoms begin between 30 and 50 years old2. At the same time, HD can be divided into three parts depending on their symptoms. There are three phases: early, middle and late. In the early stage, patients present involuntary movements, coordination problems, difficulty to think and depression in low quantities but these symptoms cannot affect completely their daily activities so, they maintain their autonomy. In the middle stage, their coordination and their capacity to think are seriously affected, so, they need help to realize normal activities. In the late stage, patients are confined to bed, need assistance and have difficulties to communicate1. Nowadays, using the CRISPR/Cas9 technique, scientist have achieved alleviate motor deficits and, in another case, they could inactivate permanently the mutant gene that causes HD. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and the endonuclease protein Cas, constitute a mechanism that acts like immune system in prokaryotes, generating a resistance against foreign DNA. This technique is used to edit genomes through insertion, change or deletion of genes using Cas9 that acts like molecular scissors that cut a specific sequence3. CRISPR/Cas9 system works with following components: sgRNA with a guide sequence, Cas9 protein and Protospacer Adjacent Motif (PAM). Scientists create a guide RNA that join with Cas9. Then, PAM triplet which is adjacent to the target site, help to ubicate the Cas9 and bind the guide sequence with the corresponding target sequence. This linkage represents the part of the genome that Cas9 is going to cut. For this, is important to consider that for each organism is needed a specific PAM triplet and a Cas9 protein according to the function that the system must achieve4. Huntington’s disease is a dominant disorder because the mutant protein (Huntingtin) which is the factor that provokes the disease. For this reason, current investigations using CRISPR/Cas9 have the objective to avoid the expression of the mutant. The present work contains a review of two cases in which the CRISPR/Cas9 technique is used to produce a reduction and permanent inactivation of mutant gene expression5, 6.

Application of the technique CRISPR/Cas9 in the reduction and permanent inactivation of Huntington’s Disease