What specific physical feature can be indicative of Williams syndrome?

The presence of elfin facial features is a hallmark characteristic of Williams syndrome. Individuals with this condition often have a distinct facial appearance that includes prominent cheeks, a broad forehead, a small chin, and a full mouth that gives a friendly expression. This unique facial profile is frequently described as "elfin," which reflects a youthful and whimsical appearance.

In contrast, the other options represent physical traits or symptoms that are not specific to Williams syndrome. Shortened fingers and toes are not a recognized feature of the syndrome. Hypotonia, while sometimes observed in individuals with Williams syndrome, is also associated with a range of other conditions and therefore is not distinctive. Macrocephaly refers to enlarged head size, which does not correlate specifically with what is observed in Williams syndrome. Elfin facial features stand out precisely because they capture the unique physical traits associated with this genetic disorder, making them a key identifying feature.