What is a hallmark feature of Patau syndrome?

Patau syndrome, also known as trisomy 13, is characterized by the presence of an extra chromosome 13 in an individual's genetic makeup. This condition leads to a range of severe developmental and physical abnormalities. Patients with Patau syndrome often exhibit specific features such as holoprosencephaly (a brain malformation), cleft lip and/or palate, polydactyly (extra fingers or toes), and congenital heart defects. The presence of the additional chromosome 13 disrupts the normal development of various organ systems, which is why the correlation between the genetic anomaly and the phenotypic manifestations is critical in diagnosing this syndrome.

In contrast, the other choices refer to different chromosomal abnormalities associated with other syndromes. For instance, trisomy 18 pertains to Edwards syndrome and is characterized by its own distinct set of features. Trisomy 21 indicates Down syndrome, which presents different clinical manifestations. Lastly, a deletion of chromosome 5p is associated with Cri du chat syndrome, which also has its specific characteristics. Thus, the diagnosis of Patau syndrome is specifically linked to trisomy 13, making it the hallmark feature of this condition.