Our observation suggests that homozygosity for the Arg-261-Gln mutation can indeed result in "mild" PKU with little or perhaps no mental retardation, but also indicates that in such women, who may go unrecognized if not screened for, blood phenylalanine is elevated enough to cause the maternal PKU syndrome in their offspring.
A 31 year old MPKU female with classical PKU (mutations P281L/P281L), diagnosed by newborn screening, had a lifelong history of poor metabolic control.