A syndrome with facial anomalies including a thin upper lip, growth delay and developmental disabilities is likely to result from either a teratogenic congenital malformation, a single gene defect (Mendelian) or a chromosomal disorder. A trait is called polygenic if multiple genes are thought to contribute to the phenotype and includes conditions like diabetes and hypertension. A polygenic disorder is the least likely diagnosis amongst the options provided and the single best answer of exclusion.