A short child with white bones

A 10-year-old boy presented with poor weight and height gain since early childhood without prior systemic illness or clinical features suggesting a specific etiology. He was born at full term through vaginal delivery with a birth weight of 2.5 kg and the perinatal and neonatal periods were unremarkable. The patient had a single right tibial fracture following a trivial trauma during early childhood.

Examination revealed frontal bossing, prominent eyes with blue sclerae, dental crowding [Figure 1a], brachydactyly with soft finger pads, and spoon-shaped nails [Figure 1b]. Anthropometric assessment showed proportionate short stature (upper segment to lower segment ratio of 1:1 and height Z score −2.61). The skeletal survey showed acro-osteolysis [Figure 1c], open posterior fontanelle [Figure 1d], osteosclerosis [Figure 1e], and notching of vertebrae [Figure 1f]. Growth hormone (GH) stimulation testing confirmed normal GH secretion. The clinical and imaging findings were consistent with pycnodysostosis (PYCD), a rare skeletal dysplasia. Genetics was planned, but could not be done due to financial constraints.

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Figure 1:

A 10-year-old boy with pycnodysostosis. (a) Dental crowding, (b) spoon-shaped nails (black arrows), (c) acro-osteolysis (white arrows), (d) open posterior fontanelle (white arrow), (e) osteosclerosis, and (f) notching of vertebrae (white arrow).

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PYCD is a rare autosomal recessive skeletal dysplasia caused by pathogenic cathepsin K (CTSK) gene variants, resulting in defective CTSK activity.^[1] Diagnosis relies on clinical features and pathognomonic radiographic findings of osteosclerosis with acro-osteolysis. Common morbidities include fracture risk, dental abnormalities, and growth failure.^[1,2] The differential diagnoses for PYCD include osteopetrosis, cleidocranial dysplasia, and idiopathic acro-osteolysis. Growth hormone stimulation testing is advised for severely stunted children as early treatment is advantageous.^[2] Early diagnosis is vital for tailored management, including fracture prevention, dental care, and growth monitoring.