Large testes in a male newborn may suggest which diagnosis?

Large testes in a male newborn can be indicative of Fragile X syndrome. This genetic condition is linked to the expansion of the CGG repeat in the FMR1 gene and is one of the most common causes of inherited intellectual disability. One of the physical features associated with Fragile X syndrome is macroorchidism, or enlarged testes, which often becomes apparent after puberty but can sometimes be noticed in infancy.

In neonates, identifying this symptom may lead healthcare providers to consider a genetic evaluation, especially if there's a family history of developmental disorders.

Other conditions such as Down syndrome and Turner syndrome are not associated with this characteristic, as they typically present with different set of clinical features. Similarly, Williams syndrome, which involves cardiovascular and other systemic anomalies, does not typically show an increase in testicular size in male infants. Therefore, regarding large testes in a male newborn, Fragile X syndrome is the most relevant diagnosis.