Deaf children born to signing parents begin to "babble" in sign at the same point in infancy that hearing infants babble speech, and proceed from there to learn a fully expressive language.
A significant number of children with mutism also have expressive language disorders, and a fairly large number come from a bilingual environment, which may add to a child's vulnerability to mutism.
In addition to language delay, apraxia often causes other expressive language disorders.
It relies on parents' reports and a very short test focusing on visual, receptive, and expressive language.
Prenatal care and good nutrition during pregnancy and early childhood may help prevent some expressive language delays.
