Ascertainment bias causes false signal of anticipation in genetic prion disease.

Am J Hum Genet
Authors
Keywords
Abstract

Anticipation is the phenomenon whereby age of onset in genetic disease decreases in successive generations. Three independent reports have claimed anticipation in Creutzfeldt-Jakob disease (CJD) caused by the c.598G > A mutation in PRNP encoding a p.Glu200Lys (E200K) substitution in the prion protein. If confirmed, this finding would carry clear implications for genetic counseling. We analyzed pedigrees with this mutation from four prion centers worldwide (n = 217 individuals with the mutation) to analyze age of onset and death in affected and censored individuals. We show through simulation that selective ascertainment of individuals whose onset falls within the historical window since the mutation's 1989 discovery is sufficient to create robust false signals both of anticipation and of heritability of age of onset. In our data set, the number of years of anticipation observed depends upon how strictly the data are limited by the ascertainment window. Among individuals whose disease was directly observed at a study center, a 28-year difference between parent and child age of onset is observed (p = 0.002), but including individuals ascertained retrospectively through family history reduces this figure to 7 years (p = 0.005). Applying survival analysis to the most thoroughly ascertained subset of data eliminates the signal of anticipation. Moreover, even non-CJD deaths exhibit 16 years anticipation (p = 0.002), indicating that ascertainment bias can entirely explain observed anticipation. We suggest that reports of anticipation in genetic prion disease are driven entirely by ascertainment bias. Guidelines for future studies claiming statistical evidence for anticipation are suggested.

Year of Publication
2014
Journal
Am J Hum Genet
Volume
95
Issue
4
Pages
371-82
Date Published
2014 Oct 02
ISSN
1537-6605
DOI
10.1016/j.ajhg.2014.09.003
PubMed ID
25279981
PubMed Central ID
PMC4185115
Links
Grant list
P50 AG023501 / AG / NIA NIH HHS / United States
MC_U123160651 / Medical Research Council / United Kingdom
P50AG023501 / AG / NIA NIH HHS / United States
Medical Research Council / United Kingdom
UL1 RR024131 / RR / NCRR NIH HHS / United States
P01 AG021601 / AG / NIA NIH HHS / United States
AG021601 / AG / NIA NIH HHS / United States
R01 AG031189 / AG / NIA NIH HHS / United States
K23 AG021989 / AG / NIA NIH HHS / United States
N01-NS-0-2328 / NS / NINDS NIH HHS / United States
R01 AG-031189 / AG / NIA NIH HHS / United States
UL1 TR000004 / TR / NCATS NIH HHS / United States