Pycnodysostosis: clinical, radiologic, and endocrine evaluation and linear growth after growth hormone therapy

Abstract

Pycnodysostosis is a rare hereditary bone abnormality with an autosomal recessive mode of inheritance. We report the clinical, radiologic, and endocrine status of 8 children with this rare disease. All patients had the characteristic phenotype of the disorder including short stature (8 of 8), increased bone density (7 of 8), separated cranial sutures (8 of 8), large fontanel with delayed closure (8 of 8), obtuse mandibular angle (8 of 8), delayed teeth eruption (8 of 8), enamel hypoplasia (7 of 8), dysplastic acromial ends of the clavicles (6 of 8), frontal bossing (6 of 8), ocular proptosis (8 of 8), and dysplastic nails (8 of 8). Developmental evaluation according to the revised Denever developmental screening showed normal motor, fine motor-adaptive language, and personal social abilities in all the children. All had normal hepatic and renal functions. Serum calcium and phosphorus concentrations were normal. Two children had low serum alkaline phosphatase concentration. Short stature is a characteristic feature of pycnodysostosis. Seven of the 8 children were born short (length standard deviation score [SDS] = -3 to -1.5). Deceleration of linear growth was significant during the first 3 years of life. All the children had height SDS below -3 at the end of their third year of life. Although short stature is a feature of this genetic disorder, defective growth hormone (GH) secretion in response to provocation with clonidine and glucagon was found in 4 of the 8 patients. These 4 patients had pituitary hypoplasia on the magnetic resonance imaging (MRI) of their brain. In addition, 3 of these 4 patients had demyelination of the cerebrum. Patients with pycnodysostosis (n = 8) had low circulating concentrations of insulin-like growth factor-1 (IGF-1) compared with normal age-matched short children with constitutional short stature (CSS). IGF-I increased significantly after injecting GH for 3 days in these patients. Physiologic replacement with GH (18 U/m(2)/week) divided in daily evening doses subcutaneously increased IGF-1 concentration and improved linear growth velocity and height standard deviation scores (HtSDS) in the 4 children with GH deficiency. These data ruled out GH resistance and proved the usefulness of GH therapy in the management of short stature in these patients. In summary, some patients with pycnodysostosis have partial GH deficiency and low IGF-1 concentration. GH therapy markedly increases IGF-I secretion and improves their linear growth. MRI study of the brain including the hypothalamic-pituitary area is recommended in these children because of the high incidence of pituitary hypoplasia and cerebral demyelination.