Arly, PKU is autosomal recessive. THe baby would not be affected unless the father was also a carrier or had PKU. If dad and mom both had pku, each baby has 100% chance of having PKU. If dad is a carrier, and mom has pku (or vice versa), each baby has a 50% chance of having pku, and a 50% chance of being a carrier (heterozygous). If dad is not a carrier, each child will be a carrier but not affected. Lawrence states that the amino acid profile of the milk of mothers with PKU being controlled by diet are normal. I have been able to find nothing about phe levels in milk of mothers who are not on the phe free diet. I wonder if the normal baby would be able to convert the phe to tyrosine fast enough to avoid brain damage? Not an experiment I would want to perform, the stakes being what they are... Catherine Watson GEnna, IBCLC (who once considered being a genetic counsellor) NYC [log in to unmask]