Microcephaly, blue eyes, fair skin, and mental retardation in a 4 year old girl with a positive ferric chloride test is indicative of which of the following?
**Core Concept**
Microcephaly, blue eyes, fair skin, and mental retardation in a child can be indicative of a genetic disorder that affects multiple systems, including the skin, eyes, and central nervous system. This combination of features is often associated with a condition that involves a defect in the metabolism of a particular amino acid.
**Why the Correct Answer is Right**
The positive ferric chloride test is a key diagnostic clue in this case. The test detects the presence of phenylketonuria (PKU), a genetic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase (PAH). This enzyme is responsible for converting the amino acid phenylalanine to tyrosine. In PKU, phenylalanine builds up in the body and can cause a range of symptoms, including microcephaly, blue eyes, fair skin, and mental retardation. The positive ferric chloride test is a rapid screening test for PKU that detects the presence of phenylketones in the urine.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not mention PKU, which is the most likely diagnosis based on the symptoms and positive ferric chloride test.
**Option B:** This option is incorrect because it does not provide a clear diagnosis or connection to the symptoms and positive ferric chloride test.
**Clinical Pearl / High-Yield Fact**
PKU is a classic example of a genetic disorder that can be prevented or treated with dietary restrictions. Early detection through newborn screening programs and a strict diet that limits phenylalanine intake can prevent the development of symptoms and improve outcomes.
**Correct Answer:** C. Phenylketonuria (PKU)