FGFR3 mutations cause wide spectrum of disorders ranging from skeletal dysplasias (hypochondroplasia, achondroplasia, and thanatophoric dysplasia), benign skin tumors (epidermal nevi, seborrhaeic keratosis, and acanthosis nigricans), and epithelial malignancies (multiple myeloma and prostate and bladder carcinoma). Hypochondroplasia is the most common type of short-limb dwarfism in children resulting from fibroblast growth factor receptor 3 (FGFR3) mutation. Acanthosis nigricans might be seen in severe skeletal dysplasia, including thanatophoric dysplasia and SADDAN syndrome, without a biochemical evidence of hyperinsulinemia. Insulin insensitivity and acanthosis nigricans are uncommonly seen in hypochondroplasia patients with FGFR3 mutations which may represent a new association. We aim to describe the association of hypochondroplasia, acanthosis nigricans, and insulin resistance in a child harboring FGFR3 mutation. To our knowledge, this is the first case report associating the p.N540 with acanthosis nigricans and the second to describe hyperinsulinemia in hypochondroplasia. This finding demonstrates the possible coexistence of insulin insensitivity and acanthosis nigricans in hypochondroplasia patients.
The localization of FGFR3 mutations causing thanatophoric dysplasia type I differentially affects phosphorylation, processing and ubiquitylation of the receptor
