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Autism is a brain development disorder that impairs social interaction and communication, and causes restricted and repetitive behavior, takes a steady course with no relapses or remissions. Autism is highly heritable, although the genetics of autism are complex and it is generally unclear which genes are responsible Autism affects many parts of the brain; how this occurs is poorly understood. Parents usually notice signs in the first two years of their child's life Each child diagnosed with an autistic disorder differs from every other and so general descriptions of autistic behavior and characteristics do not apply equally to every child. Still, the common impairments in social interaction, communication and imagination, and rigid, repetitive behaviors make it possible to recognize children with these disorders, as they differ markedly from healthy children in many ways Many parents of autistic children sense that something is not quite right even when their children are infants. The infants may have feeding problems, dislike being changed or bathed, or fuss over any change in routine. They may hold their bodies rigid, making it difficult for parents to cuddle them. Or, they may fail to anticipate being lifted, lying passively while the parent reaches for them, rather than holding their arms up in return. Most parents of autistic children become aware of the strangeness of these and other behaviors only gradually.