Which characteristic does NOT apply to adult polycystic kidney disease?

Adult polycystic kidney disease (APKD) is primarily characterized by the development of numerous cysts in the kidneys, which typically leads to kidney enlargement rather than small kidneys. In fact, one of the hallmark features of APKD is the gradual increase in kidney size due to cyst formation, especially in the early stages of the disease. As the disease progresses, the kidneys can become significantly enlarged, and this enlargement is often associated with increased echogenicity on ultrasound due to the cystic changes.

The other characteristics accurately reflect the nature of APKD: it is indeed an autosomal dominant inheritance pattern (meaning that only one copy of the mutated gene from an affected parent is required for a child to inherit the disease), can be associated with cysts in other organs such as the liver and pancreas, and symptoms commonly do not appear until the third or fourth decade of life. Hence, the statement regarding bilateral small, echogenic kidneys does not apply to adult polycystic kidney disease.