Pycnodysostosis With Papilledema and Isolated Low Parathyroid Hormone Levels in an Eight-Year-Old Girl: A Genetically...

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia resulting from pathogenic variants in the CTSK gene, which encodes cathepsin K, a lysosomal cysteine protease expressed in osteoclasts. Deficiency of this enzyme leads to defective bone resorption and generalized osteosclerosis. We report an 8-year-old girl, the firstborn of a third-degree consanguineous marriage, who presented with poor height and weight gain since birth and delayed developmental milestones, including independent walking at 2 years of age. Physical examination revealed proportionate short stature with microcephaly and brachycephaly. Craniofacial findings included frontal bossing, beaked nose, low-set posteriorly rotated ears, micrognathia and a high-arched fissured palate with dental crowding and supernumerary teeth. Thickened palmar skin, pectus carinatum, and saddle toe deformity were also seen. Fundoscopic examination demonstrated bilateral papilledema. Radiographic evaluation showed diffuse cranial sclerosis, wormian bones, hypoplastic clavicles, acro-osteolysis, and generalized increased bone density. Endocrine assessment revealed isolated low parathyroid hormone levels, an exceptionally rare association. Molecular genetic testing by clinical exome sequencing (CES) identified a homozygous pathogenic variant in exon 6 of the CTSK gene, establishing the diagnosis of pycnodysostosis. The patient was initiated on recombinant growth hormone therapy and referred for multidisciplinary follow-up, including endocrinology, dentistry, orthopedics, and ophthalmology. This case underscores both classical manifestations and unusual findings such as papilledema and low PTH levels. Early diagnosis through careful clinical evaluation and genetic confirmation enables timely initiation of appropriate interventions. Growth hormone therapy demonstrated consistent improvement in linear growth, emphasizing the potential for better long-term outcomes. A coordinated multidisciplinary approach remains essential to enhance prognosis and overall quality of life in children with this rare skeletal dysplasia.