Receptive Language the ability to comprehend words and sentences. Begins as early as birth and increases with each stage in development. By 12 months a child begins to understand words and responds to his name and may respond to familiar words in context. By 18 to 20 months a child identifies familiar people by looking when named (e.g., Where’s mommy?), gives familiar objects when named (e.g., Where’s the ball?), and points to a few body parts (e.g., Where’s your nose?). These skills commonly emerge slightly ahead of expressive language skills. ¹⁶¹

Relationship Development Intervention (RDI) is a treatment program for autism spectrum disorders (ASD), based on the belief that the development of dynamic intelligence is the key to improving the quality of life for individuals with autism. RDI focuses on cultivating the building blocks of social connection -- such as referencing, emotion sharing, coregulation, and experience sharing -- that normally develop in infancy and early childhood. RDI is a family-based program, where trained consultants support families to alter their interaction and communication styles. ¹⁶³

Rett Syndrome is a very rare disorder in which patient has symptoms associated with PDD along with problems with physical development. They generally lose many motor, or movement, skills – such as walking and use of hands – and develop poor coordination. Condition has been linked to defect on the X chromosome, so it almost always affects girls. ¹⁶⁵