I have a brother that was a PK child. Never mind what the acronym stands for, it amounts to his being unable to process certain proteins. He was born in a time when tests for PK were rare, and by the time his was caught it was too late. He suffered mental retardation as a result.
Mom might have aborted him had she known. Here's the odd thing though; since Dad died, the two of them live together in the house. Without him there I don't know what Mom would do. He is mentally 9-10 years-old, and is the sweetest soul I know. He is what would appear to be a hardship to some, but I see him as a blessing.