Final answer:
The most distinguishing symptom before age 2 is hypotonia, which refers to decreased muscle tone. This can make it difficult for infants and young children to sit, stand, or walk independently.
Step-by-step explanation:
The most distinguishing symptom before age 2 is hypotonia. Hypotonia refers to decreased muscle tone, which can result in decreased strength and movement.
This can make it difficult for infants and young children to sit, stand, or walk independently. For example, a baby with hypotonia may have trouble holding their head up or may appear floppy when picked up.