Answer:
Down syndrome and fragile X syndrome
Step-by-step explanation:
The two most common genetic causes of intellectual disability are Down syndrome and fragile X syndrome.
Fragile X syndrome is an inherited condition that determines changes in intellectual development and behavior. Although considered to be the second most common cause of genetic disability - the first being Down syndrome - the disease is poorly known, as its findings are only around 30 years old. Unlike Down syndrome which is better known and widespread.