Stock No. 027411 was formerly associated with CHDI Foundation colony Stock No. 370504 [CHDI-81003005].

Huntington's disease (HD) is an autosomally dominant, fatal neurodegenerative disorder characterized by uncontrolled movements, psychiatric disturbances and cognitive impairment. HD is caused by an unstable trinucleotide (polyglutamine) repeat expansion in the huntingtin gene (HTT; HD or Hdh).


The HdhQ20 knock-in allele (Hdh^Q20) has a chimeric mouse:human huntingtin exon 1 (Hdh:HD exon 1) encoding the human version of the polyglutamine/polyproline-rich segment with 18 CAG repeats [(CAG)₁₈CAACAG].
The polyglutamine stretch in the mutant huntingtin product, as denoted in the name of the Hdh^Q20 knock-in allele, is two residues longer than the number of CAG units in the repeat due to invariant, penultimate exon 1 CAA,CAG codons immediately downstream. The CAG repeat number in the Hdh^Q20 knock-in allele is reported to be stable (see note on CAG stability below). Mutant mice accurately express the mouse/human hybrid huntingtin protein. Homozygous and heterozygous mice are viable and fertile with normal lifespans.

This Huntington's disease mouse model is available by way of a collaborative effort between CHDI Foundation, Dr. Marcy E. MacDonald (Massachusetts General Hospital) and The Jackson Laboratory.

While pure CAG sequences in exon 1 may be subject to germline or somatic instability, and may expand or contract, the CAG repeat number in the Hdh^Q20 knock-in allele is reported to be stable. When using lines with unstable CAG repeat length, it is strongly recommended the CAG repeat number be quantified in all the experimental animals; all animals in all experimental groups should carry comparable CAG repeat sizes. CAG repeat sizing of HD mice should be done using high-resolution methods as assays based on agarose gel electrophoresis typically do not provide sufficient resolution to accurately measure CAG repeat numbers. If labs do not have access to the appropriate equipment for determining CAG repeat length, CAG repeats can be evaluated on a fee-for-service basis by Laragen, Inc.