To date, the reason is unknown for the high prevalence of phenylalanine hydroxylase (PAH) mutations causing phenylketonuria (PKU) in extant European populations. However, molecular genetic data generated over the last decade suggest that the concomitant excess of (unaffected) PKU carriers is at least in part the result of overdominant selection ("heterozygous advantage"). Such selection would have acted upon several different mutations in different historical populations. The exact nature of the underlying selective mechanism is unknown; its elucidation requires further investigation.
Copyright 2003 Wiley-Liss, Inc.