Table 4 Allele frequencies for polymorphisms in TCERG1 and GRIN2A.

Gene	Allele number or genotype	Presumed (Gln‐Ala)n repeat number	Population allele frequency (%)	Mean age of onset
TCERG1	289	35	2.5	29.3
	294	36	0.8	41.4
	300	37	0.2	38.5
	306	38	95.4	34.8
	318	40	0.7	26.3
	328	41.5	0.3	–
GRIN2A	C/C		4.7	33.8
	C/T		39.5	32.3
	T/T		55.8	36.2

TCERG1 genotypes were determined for 728 people (410 of whom are affected with Huntington's disease). No affected people had a TCERG1 328 allele. Repeat length was inferred on the basis of the length of the amplified PCR products and the published sequence. GRIN2A genotypes were determined for 731 people (405 of whom were affected with Huntington's disease). Allele frequencies are calculated from all people. Mean age of onset is calculated from affected people.