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Difficulty: HardPediatric Neurologic Disorders

During a routine health maintenance visit, a physician evaluates a 2-year-old girl due to parental concerns regarding significant behavioral changes. The parents state that she achieved all early developmental milestones appropriately, including sitting unassisted at 6 months and saying single words at 12 months. However, over the past 8 months, she has lost her vocabulary and no longer makes purposeful reaching movements with her hands. Instead, she continuously claps and wrings her hands together. The parents also report intermittent episodes where she breathes very rapidly and forcefully, occasionally leading to mild wheezing, followed by periods of breath-holding. Physical examination reveals an alert child who avoids eye contact. Her head circumference has dropped from the 50th percentile at age 6 months to the 5th percentile currently. She exhibits no signs of acute distress and remains afebrile. Based on the most likely underlying condition, which of the following is the most appropriate next step in management or evaluation?

  1. A
    Schedule a follow-up in 6 months, as temporary regressions in language and motor skills are common in healthy toddlers
  2. B
    Obtain blood and cerebrospinal fluid cultures, then administer broad-spectrum intravenous antibiotics
  3. Order molecular genetic testing for an X-linked dominant mutationAnswer
  4. D
    Initiate an inhaled short-acting beta-agonist to manage the episodes of wheezing and rapid breathing
  5. E
    Immediately notify child protective services regarding suspected physical abuse based on the hand findings

Answer

Order molecular genetic testing for an X-linked dominant mutation
The patient's clinical presentation is highly characteristic of Rett syndrome, a neurodevelopmental disorder that occurs almost exclusively in girls. It is characterized by normal development for the first 6 to 18 months of life, followed by a severe regression in language and motor milestones. Hallmark features include acquired microcephaly (evidenced by the deceleration of head growth from the 50th to the 5th percentile), loss of purposeful hand movements, the development of stereotypic hand movements (such as continuous wringing or clapping), and autonomic breathing abnormalities (hyperventilation alternating with breath-holding). The condition is caused by a de novo X-linked dominant mutation in the MECP2 gene. Therefore, molecular genetic testing is the most appropriate next step to confirm the diagnosis.

Step-by-Step Solution

1
Analyze the developmental timeline.
Normal early development followed by severe regression (loss of language and purposeful hand use) starting around 18 months of age.
Identifying the pattern of milestone acquisition and loss is critical for differentiating neurodevelopmental disorders.
2
Identify hallmark physical and behavioral signs.
Acquired microcephaly (drop in head circumference percentiles), stereotypic hand-wringing, and autonomic breathing abnormalities.
These specific signs narrow the differential diagnosis from general developmental delay to a specific neurogenetic syndrome.
3
Determine the underlying diagnosis and appropriate diagnostic test.
The clinical picture is classic for Rett syndrome. The next step is genetic testing for a mutation in the MECP2 gene, which has an X-linked dominant inheritance pattern.
Rett syndrome is diagnosed clinically but confirmed definitively via molecular genetic testing.

Key Concept

Rett syndrome is characterized by normal early development followed by regression, acquired microcephaly, stereotypic hand movements, and autonomic breathing abnormalities, and is confirmed via MECP2 gene testing.
Estimated Time:1m 30s
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Topics

Pediatric Neurologic Disorders

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