Complex sentence: Moderate to severe defects may cause mental retardation, spastic quadriparesis, athetoid movements, endocrine disorders, epilepsy and other serious conditions; mild brain defects may only cause learning or behavior problems with few motor impairments.
Split into simpler sentences: Moderate to severe defects may cause mental retardation, spastic quadriparesis, athetoid movements, endocrine disorders, epilepsy and other serious conditions. Whereas, mild brain defects may only cause learning or behavior problems with few motor impairments.