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]