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Difficulty: EasyPediatric Genetic and Metabolic Disorders

A 10-month-old boy is brought to the pediatrician by his parents for a well-child check. The parents are concerned because he is not yet sitting without support and has stopped babbling. They also report that his diapers have a distinct "musty" odor. On physical examination, the boy is noted to have very fair skin, blonde hair, and blue eyes, which contrasts significantly with his parents' dark complexions. An intensely itchy, erythematous, scaly rash is present on his cheeks and the extensor surfaces of his arms. A basic metabolic panel is unremarkable. Assuming the diagnosis is confirmed, which of the following is the most appropriate long-term management for this patient's underlying condition?

  1. A
    Reassurance and routine follow-up for isolated motor delay
  2. B
    Application of topical mupirocin to the face and arms
  3. C
    Initiation of daily levothyroxine therapy
  4. Restriction of dietary phenylalanineAnswer
  5. E
    Intravenous administration of sodium bicarbonate

Answer

The most appropriate long-term management is the restriction of dietary phenylalanine.
The correct answer directly addresses the underlying pathophysiology of Phenylketonuria (PKU). This patient's presentation of developmental delay, a distinct 'musty' or 'mousy' odor, fair skin and hair (due to lack of tyrosine for melanin synthesis), and an eczematous rash is the classic clinical vignette for PKU. The primary, essential treatment to prevent progressive and irreversible intellectual disability is a strict, lifelong diet restricted in phenylalanine.

Step-by-Step Solution

1
Identify the clinical syndrome based on the physical exam and history.
The patient has developmental delay, a 'musty' body odor, fair pigmentation (blonde hair, blue eyes), and eczema.
This specific combination of signs is the classic tetrad for Phenylketonuria (PKU).
2
Determine the underlying pathophysiology of the identified condition.
PKU is caused by a deficiency in the enzyme phenylalanine hydroxylase, leading to toxic accumulation of phenylalanine and decreased production of tyrosine (which causes the decreased melanin and fair pigmentation).
Understanding the biochemical defect dictates the therapeutic approach.
3
Select the most appropriate management.
The cornerstone of treatment is a lifelong diet restricted in phenylalanine, along with tyrosine supplementation.
This prevents further neurological damage and intellectual disability.

Key Concept

Phenylketonuria (PKU) presentation and management
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Topics

Pediatric Genetic and Metabolic Disorders

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