How does transposition of the great arteries typically present in newborns?

Transposition of the great arteries (TGA) is a critical congenital heart defect where the pulmonary artery and aorta are switched. In newborns with TGA, the hallmark presentation is severe cyanosis soon after birth. This happens because the blood is circulated in two separate circuits: deoxygenated blood returns to the body without being oxygenated, leading to a significant drop in oxygen saturation levels.

While a heart murmur might be detected depending on any accompanying structural heart defects, it is not a defining feature of TGA. Difficulty in breathing can occur due to other complications or associated cardiac issues but is not the primary symptom of TGA. Hypotonia is generally not associated with this condition and does not relate specifically to the hemodynamic changes caused by TGA. Therefore, severe cyanosis shortly after birth is the critical and defining characteristic of this condition, making it the correct answer.