Aplasia cutis congenita in a CDC42-related developmental phenotype.

Cell division cycle 42 (CDC42) is a small Rho GTPase, which serves as a fundamental intracellular signal node regulating actin cytoskeletal dynamics and several other integral cellular processes. CDC42-associated disorders encompass a broad clinical spectrum including Takenouchi-Kosaki syndrome, autoinflammatory syndromes and neurodevelopmental phenotypes mimicking RASopathies. Dysregulation of CDC42 signaling by genetic defects in either DOCK6 or ARHGAP31 is also considered to play a role in the pathogenesis of Adams-Oliver syndrome (AOS). Here, we report a mother and her child carrying the previously reported pathogenic CDC42 variant c.511G>A (p.Glu171Lys). Both affected individuals presented with short stature, distinctive craniofacial features, pectus deformity as well as heart and eye anomalies, similar to the recently described Noonan syndrome-like phenotype associated with this variant. Remarkably, one of the patients additionally exhibited aplasia cutis congenita of the scalp. Multi-gene panel sequencing of the known AOS-causative genes and whole exome sequencing revealed no second pathogenic variant in any disease-associated gene explaining the aplasia cutis phenotype in our patient. This observation further expands the phenotypic spectrum of CDC42-associated disorders and underscores the role of CDC42 dysregulation in the pathogenesis of aplasia cutis congenita.