Large testes in a male newborn may suggest which condition?

Large testes in a male newborn are most commonly associated with Klinefelter syndrome. Klinefelter syndrome is a genetic condition resulting from the presence of an extra X chromosome in males (47,XXY), which often leads to physical and developmental characteristics, including larger-than-normal testes (hypertrophy).

While fragile X syndrome involves an expansion of a specific gene that can lead to developmental issues and might present with other signs such as macroorchidism (larger than average testes) in older children and adolescents, it is not typically used to describe the newborn presentation.

Down syndrome and Turner syndrome have distinct characteristics that do not include large testes in male newborns. Down syndrome is characterized by features such as hypotonia and distinct facial features while Turner syndrome affects females, leading to traits such as short stature and absence of secondary sexual development.

Therefore, in the context of the initial question, large testes in a male newborn point towards Klinefelter syndrome as the most appropriate condition associated with this physical characteristic.