A newborn presents with cleft lip and palate, extra fingers (polydactyly), a small head (microcephaly) accompanied by holoprosencephaly, and an ectodermal defect on the scalp. Which chromosomal abnormality is most likely responsible for these findings?

Explanation

The combination of cleft lip and palate, polydactyly, microcephaly with holoprosencephaly, and ectodermal scalp defects is characteristic of Patau syndrome (Trisomy 13). Down syndrome (Trisomy 21) and Edwards syndrome (Trisomy 18) have different clinical features, while Turner syndrome affects females with monosomy X and does not present with these anomalies.