Unless the condition is detected and treatment is initiated soon after birth, phenylalanine builds up in the blood and body tissues and is toxic to the brain, usually resulting in severe mental retardation. Treatment requires eliminating foods naturally high in protein to remove phenylalanine from the diet within the first weeks of life and maintaining a protein-restricted diet through adolescence and perhaps throughout life. Risks as a result of maternal PKU occur when a woman with PKU becomes pregnant after having discontinued the low phenylalanine diet. Discontinuing the diet during childhood or on entering adulthood was common practice until young women with PKU began to have babies with mental retardation. The medical community then realized that if the mother is not on a low phenylalanine diet, the fetus will be exposed to toxic levels of phenylalanine that may result in severe mental retardation or death.
Hypothyroidism results from an inadequate supply of the thyroid hormone, thyroxine.
Untreated, the child's growth will be stunted, and mental retardation will occur from lack of stimulation of the brain by the hormone thyroxine. All states now screen for hypothyroidism using the same filter paper blood spots as for PKU screening. The condition is treated by initiating thyroid hormone replacement treatment as soon as possible after birth. Galactose is the major sugar found in milk. It is normally converted to glucose, another simple sugar, but in galactosemia, the enzyme needed for this conversion is missing.