Kosaki overgrowth syndrome: A newly identified entity caused by pathogenic variants in platelet‐derived growth factor receptor‐beta

Specific classes of de novo heterozygous gain‐of‐function pathogenic variants of the PDGFRB (platelet‐derived growth factor receptor‐beta) cause a distinctive overgrowth syndrome, named the Kosaki overgrowth syndrome (KOGS) (OMIM #616592). Until now, six patients with this condition have been reported in the literature. In addition to skeletal overgrowth, these patients exhibit hyperelastic, translucent, and fragile skin, scoliosis, progressive loss of subcutaneous adipose tissue, skull deformity, infantile myofibromas, neuropsychiatric symptoms, and arachnoid cysts in the posterior fossa and periventricular white matter signal abnormalities on neuroimaging. This constellation of phenotypes clearly distinguishes KOGS from other PDGFRB ‐related disorders, including idiopathic basal ganglia calcification, infantile myofibroma, and Penttinen‐type premature aging syndrome. From a molecular standpoint, PDGFRB is a dimeric receptor tyrosine kinase that plays critical roles in cell growth and tumorigenesis. The two known types of pathogenic variants (p.(Pro584Arg) and p.(Trp566Arg)) of the PDGFRB that cause KOGS are exclusively located in the juxtaglomerular domain that regulates autoactivation/inhibition of PDGFRB. In‐vitro evidence suggests that p.(Pro584Arg) represents a gain‐of‐function pathogenic variant. Inhibition of PDGFRB activity using multi‐kinase inhibitors appears to be a potentially promising therapeutic approach. Investigation of the molecular mechanisms underlying the pathogenesis of this disease using induced pluripotent stem cells is under way. Presence of skeletal overgrowth, distinctive facial features, characteristic hyperelastic and fragile skin, and cerebral white matter lesions with neuropsychiatric symptoms should prompt genetic analysis of the PDGFRB .