Table 2.

Construct validity in polyQ models

Animal model properties	Higher construct validity (arbitrary)	Lower construct validity (arbitrary)
Mutation	Pure CAG tract	Mixed CAA/CAG tract
Adult length of polyQ	As in human	Longer than in human
Juvenile length of polyQ	As in human	Longer than in human
Gene context	Human gene	Nonhuman gene
Translated sequence (exons)	Full gene models	Fragment models
5′UTR, 3′UTR, introns	Full gene models	Fragment and cDNA models;
Promoter	PolyQ promoter	Non-polyQ promoter
polyQ mRNA and protein	Level equal to level of non-mutant gene of a host	Much higher or much lower expression level
Number of transgene copies	1	2 or more
Single allele or biallelic	Two alleles with various CAG tract (like in patients)	Single allele
Model generation process	Targeted	Random
Host species	Primates > swine > mouse ≈ rat	Fruit fly > C. elegans > yeast