International Board of Certified Lactation Consultant (IBCLC) Practice Exam

Which of the following conditions can lead to adverse effects with a complete diet of breastmilk due to its amino acid toxicity?

1. Galactosemia

2. Phenylketonuria

3. Lactose intolerance

4. Hyperbilirubinemia

The correct answer is: Phenylketonuria

Phenylketonuria (PKU) is a genetic disorder that results in the inability to metabolize phenylalanine, an amino acid found in many protein-containing foods, including breastmilk. Individuals with PKU cannot convert phenylalanine into tyrosine due to a deficiency in the enzyme phenylalanine hydroxylase. As a result, if an infant with PKU consumes breastmilk, the high levels of phenylalanine can accumulate in the bloodstream, leading to toxic effects, including serious neurological damage. In contrast, while galactosemia involves the inability to metabolize galactose, lactose intolerance primarily affects the digestive system and does not lead to amino acid toxicity. Hyperbilirubinemia, related to liver function and bilirubin levels, also does not pertain to amino acid metabolism. Therefore, among the given options, phenylketonuria is the condition most directly associated with adverse effects due to amino acid toxicity from a complete diet of breastmilk.