Clinical scenario:
A 2-year-old girl is brought with loss of previously acquired speech and hand skills. She was developing normally during infancy. Her head circumference was at the 90th centile at birth but has progressively crossed downwards and is now at the 50th centile. Examination shows reduced purposeful hand use with repetitive hand movements. Which of the following is the most likely diagnosis?
A. Achondroplasia
B. Benign familial macrocephaly
C. Fragile X syndrome
D. Rett syndrome
E. Sotos syndrome
Correct answer & Explanation:
Answer: D. Rett syndrome
Explanation
Rett syndrome is characterized by normal early development followed by developmental regression, particularly loss of acquired hand skills and language, with the development of stereotypic hand movements. A characteristic feature is postnatal deceleration of head growth, resulting in acquired microcephaly.
The other conditions are less consistent with this pattern. Sotos syndrome and benign familial macrocephaly are associated with larger head size, while Fragile X syndrome may cause developmental delay and macrocephaly but does not classically cause progressive deceleration of head growth. Achondroplasia has disproportionate short stature and characteristic skeletal features.
