A life table for onset of Huntington's chorea.

Accurate quantitative assessment of risk in Huntington's chorea necessitates unbiased estimation of the distribution of age at onset. Previous studies have quoted the mean observed age at onset but this is biased, containing on contribution from heterozygotes who have not manifested, which takes due account of such censored heterozygotes; it demonstrates a considerably older median age onset than hitherto been reported.