Pharmacogenetic hypersensitivity to somatropin in a child with severe growth hormone deficiency and MC4R p.V166I variant.
Ertugrul Sancak, Muammer Büyükinan, Ahmet Fatih Yılmaz et al.
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Case in brief
A boy with multiple pituitary hormone deficiencies and severe growth hormone deficiency began somatropin at 57 months of age, when his height and growth velocity were low. He carried a heterozygous MC4R p.V166I variant. At 0.03 mg/kg/day, IGF-1 rose from -3.35 SDS to +8.00 SDS, height velocity accelerated to 16 cm/year, and bone age advanced by approximately 4 years over 23 months, with mandibular prognathism. The authors considered the response suggestive of an interaction between MC4R signaling and the GH/IGF-1 axis.
What made this case unusual
The striking response occurred despite severe, biochemically confirmed growth hormone deficiency: marked IGF-1 elevation accompanied rapid linear growth, advanced bone age, and mandibular prognathism in a child with MC4R p.V166I.
Diagnostic / clinical pearl
In a child with MC4R p.V166I receiving somatropin, the authors suggest careful dose titration and close IGF-1 monitoring because responsiveness may be unusually pronounced.