Trisomy 18 is a chromosomal condition associated with severe intellectual disability and abnormalities in many parts of the body. Affected individuals often have a low birth weight; a small, abnormally shaped head; a small jaw and mouth; clenched fists with overlapping fingers; heart defects; and abnormalities of other organs.^[1] Due to the presence of several life-threatening medical problems, fifty percent of infants with this condition do not survive beyond the first week of life. Some children have survived to teenage years, but with serious medical and developmental problems.^[2] Most cases of Trisomy 18 result from having three copies of chromosome 18 in each cell in the body instead of the usual two copies. Most causes are not inherited and occur by chance.^[1]

• Genetics Home Reference (GHR) contains information on Trisomy 18. Click on the link to go to GHR and review the information.
• MedlinePlus, a Web site designed by the National Library of Medicine to help you research your health questions, provides more information about this topic. Click on the link to view this information.
• Medscape Reference provides information on this topic. Click on the link to view this information. You may need to register to view the medical textbook, but registration is free.
• The National Organization for Rare Disorders (NORD) is a federation of more than 130 nonprofit voluntary health organizations serving people with rare disorders. Click on the link to view information on this topic.
• Orphanet is a European reference portal for information on rare diseases and orphan drugs.  Access to this database is free of charge.  Click on the link to read information on this topic.
• PubMed is a searchable database of medical literature and lists journal articles that discuss Trisomy 18. Click on the link to view a sample search on this topic.

• The Social Security Administration has included this condition in their Compassionate Allowances Initiative. This initiative speeds up the processing of disability claims for applicants with certain medical conditions that cause severe disability. More information about Compassionate Allowances and applying for Social Security disability is available online.