Pycnodysostosis: A Growth Hormone Responsive Skeletal Dyspla
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.

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.

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 .

Conclusively, it is important to consider GH therapy in children with pycnodysostosis, with the greatest benefit seen in children started at a young age.