These are diseases and disorders affecting more than one system of the body.  They are typically but not always genetically linked. 

Social Security has a specific listing for one of these disorders, i.e., non-mosaic Down syndrome.  However, there are many others that can cause deviation from or interruption of the normal functions of the body or interfere with development.  They include a variety of congenital anolmalies, chromosomal disorders, dysmorphic syndromes, metabolic disorders and perinatal infectious diseases.  Examples of such disorders include triple X (XXX) syndrome, fragile X syndrome, phenylketonuria (PKU), caudal regression syndrome and fetal alcohol syndrome.  

Social Security evaluates the specific effects of these disorders under the listing criteria of any affected body system.  If no listing is met, disability is determined based on the extent to which the symptoms associated with a given disorder limit an individual's ability to meet the physical and mental aspects of competitive work.