Pycnodysostosis: A Growth Hormone Responsive Skeletal Dysplasia

OBJECTIVE: Pycnodysostosis is commonly associated with growth hormone (GH) deficiency and responds well to GH therapy with achievement of normal or near-normal height and restoration of body proportions. CASE REPORT: A 22-month-old extremely short (−4.05 height standard deviation score) disproportionate boy with skeletal dysplasia presented to clinic. Skeletal survey, genetic panel, magnetic resonance imaging, and an insulin-like growth factor generation tests were performed. RESULTS: Skeletal survey showed increased bone density with classic features of pycnodysostosis, subsequently confirmed to be due to a deleterious homozygous frameshift mutation in CTSK. Uniquely among skeletal dysplasias, GH deficiency is a common association, secondary to pituitary hypoplasia. Magnetic resonance imaging confirmed pituitary hypoplasia and he subsequently underwent an insulin-like growth factor generation test that demonstrated biochemical responsiveness to GH therapy. This was thought to be safer than a classic GH stimulation test, in view of his very small size. Subsequently, his height has markedly improved on GH therapy. His height is now −2.25 SD, with an annualized growth velocity of 9.65 cm/y over a period of 18 months . CONCLUSION: It is important to consider GH therapy in children with pycnodysostosis, with the greatest benefit seen in children started at a young age.