That is, unlike the carbon-only ring like in benzene and napthalene, there are other elements in the backbone, such as in pyrimidine and purine.
... Acrodermatitis[?] Acrodysostosis[?] Acrodysplasia scoliosis[?] Acrofacial dysostosis ambiguous genitalia[?] Acrofacial dysostosis atypical postaxial[?] ...