Molecularly proven hypochondroplasia with cloverleaf skull deformity: a novel association.

We report on a case of cloverleaf skull deformity in a patient with hypochondroplasia, a disorder which has not been previously associated with this anomaly. Hypochondroplasia is a bone dysplasia caused by mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. Cloverleaf skull is a trilobar skull deformity which is etiologically and genetically heterogeneous and occurs in association with a number of disorders which result from mutations in the fibroblast growth factor receptor genes. Our patient demonstrated one of the common FGFR3 mutations identified in hypochondroplasia, a C-to-A change at nucleotide 1620 (C1620A) in the tyrosine kinase domain. The occurrence of a cloverleaf skull deformity appears to represent an example of variable expressivity in hypochondroplasia and suggests that additional factors other than a specific mutation can modify the phenotype in this disorder. In addition, identification of another FGFR mutation associated with cloverleaf skull further illustrates the genetic heterogeneity of this anomaly.