A newborn female presents with edema of the hands and feet and a cytic mass in the neck. What condition is likely indicated by a 45XO karyotype?

A karyotype of 45XO indicates the presence of Turner syndrome, a condition resulting from the complete or partial absence of one of the X chromosomes in females. In newborns, Turner syndrome typically presents with physical anomalies such as swelling (lymphedema) of the hands and feet, which is often noticed at birth. Additionally, these individuals may have congenital abnormalities, including neck masses often associated with cystic hygromas due to lymphatic malformations.

In this case, the presentation of hand and foot edema, along with the neck mass, aligns well with the classic findings of Turner syndrome. This condition primarily affects females and is characterized by short stature, ovarian failure, and various physical findings that can include neck webbing and cardiac anomalies.

The other syndromes mentioned are associated with different karyotypes and physical manifestations. Down syndrome (trisomy 21) typically presents with distinct facial features and possible heart defects, while Edwards syndrome (trisomy 18) and Klinefelter syndrome (47XXY) have their unique presentations that do not match the symptoms described in the question.