PKU is a recessive disorder.  It is caused by inheriting two defective
copies of the gene for phenylalanine hydroxylase, thereby having and
absence of this liver enzyme.  Children without PH are unable to
metabolize phenylalanine into tyrosine, and the phenylalanine builds up
to toxic levels in the nervous system, causing mental retardation and
other problems.

Human milk contains lower levels of phenylalanine than does formula, so
infants with PKU can be given some human milk and some special
phenylalanine free formula, the balance to be determined by blood
tests.  People with PKU used to be maintained on a low phe diet until
about age 10, but now the diet is recommended for life.

There is NO defect in the mother's ability to produce phenylalanine in
her milk, whether she is heterozygous or homozygous for PKU herself.

I hope this answers your question.
--
Catherine Watson Genna, IBCLC  New York City  mailto:[log in to unmask]

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