 However, there is some controversy in the terminology because virtually any malformation will involve neuroblast migration, either primarily or secondarily.Symptoms vary according to the abnormality, but often feature poor muscle tone and motor function, seizures, developmental delays, mental retardation, failure to grow and thrive, difficulties with feeding, swelling in the extremities, and a smaller than normal head.Most infants with an NMD appear normal, but some disorders have characteristic facial or skull features that can be recognized by a neurologist.