Studies have shown us that delayed motor development is present in 90%-100% of children with Prader-Willi Syndrome (PWS). The rule of thumb is that early milestones are reached in about double the "normal" age. For example, kids with PWS often sit at 12 months and walk at 24 months. The majority of children are able to walk and it is rare for a child to never walk. Of course, children may stop walking if their weight increases to the point that walking is very difficult.
The exact reason for delays in walking and sitting in children is not known, but there are two big theories right now. One is that the extreme floppiness (hypotonia) and muscle weakness causes the problems in sitting and walking. This weakness may be caused by the high amount of fat and low amount of muscle (even in underweight babies). The second theory is that children with PWS have fewer motor neurons at birth.
The good news is that there are several studies that show that use of growth hormone therapy in babies and children before age 3 combined with physical therapy helps kids in reaching their milestones faster by increasing muscle strength. There has also been an increase in speaking and cognitive skills shown that come as well. There is also evidence that growth hormone helps the motor neurons in the motor cortex work better.
To learn more about specific kids and therapy, reach out to one of the excellent PWS support groups like the Prader-Willi Syndrome association.
