Expansion of the phenotype of Kosaki overgrowth syndrome

Skeletal overgrowth is a characteristic of several genetic disorders that are linked to specific molecular signaling cascades. Recently, we established a novel overgrowth syndrome(Kosaki overgrowth syndrome, OMIM #616592) arising from a de novo mutationin PDGFRB, that is, c.1751C>G p.(Pro584Arg). Subsequently, other investigators provided in vitro molecular evidence that this specific mutation in the juxtamembrane domain of PDGFRBcauses an overgrowth phenotype and is the first gain-of- function pointmutation of PDGFRBto be reported in humans. Here, we report the identification of a mutation in PDGFRB, c.1696T>C p.(Trp566Arg), in two unrelated patients with skeletal overgrowth, further confirming the existence of PDGFRB-related overgrowth syndromearising from mutations in the juxtamembrane domain of PDGFRB. A review of all four of these patients with an overgrowth phenotype and PDGFRBmutations revealed postnatal skeletal overgrowth, premature aging, cognitive impairment, neurodegeneration, and a prominent connective tissue component to this complex phenotype. From a functional standpoint, hypermorphic mutations in PDGFRBlead to Kosaki overgrowth syndrome, infantile myofibromatosis(OMIM #228550), and Penttinen syndrome (OMIM #601812), whereas hypomorphic mutations lead to idiopathic basal ganglia calcification(OMIM #615007). In conclusion, a specific class of mutations in PDGFRBcauses a clinically recognizable syndromic form of skeletal overgrowth.