There are a number of things that can cause developmental disabilities. Some congenital anomalies resulting from genes can bring developmental disabilities in varying degrees. Down Syndrome is an example, but there are many with genetic causes.
Brain injury (including brain damage that results from oxygen deprivation or trauma) can be another cause. When brain injury is serious enough to interfere with the normal brain development that takes place during a child's early years, developmental disabilities may result. It is important to note that not all brain injuries in childhood result in developmental disabilities. It may also be worth noting that children are said to stand a better chance of recovering from some brain injuries compared with adults.
Another possible cause is extreme neglect of a child. Many of us have seen stories about healthy, young, children being confined to cribs (in places like orphanages or abusive homes); and eventually developing serious development disabilities.
In the first few years of life children's brains are developing connections (synapses). Without the kind of nurturing required for the right kind of brain development, neglected children's brains can lose the potential for developing the right kind of brain connections. Children require adequate nurturing and nutrition in order to develop properly.
Some children with Autism (not all) may become seriously developmentally delayed.