Trisomy 13

Trisomy 13 is a type of chromosome disorder characterized by having 3 copies of chromosome 13 in cells of the body, instead of the usual 2 copies. In some people, only a portion of cells contains the extra chromosome 13 (called mosaic trisomy 13), whereas other cells contain the normal chromosome pair. Trisomy 13 causes severe intellectual disability and many physical abnormalities, such as congenital heart defects; brain or spinal cord abnormalities; very small or poorly developed eyes (microphthalmia); extra fingers or toes; cleft lip with or without cleft palate; and weak muscle tone (hypotonia). Most cases are not inherited and result from a random error during the formation of eggs or sperm in healthy parents. Trisomy 13 is diagnosed based on the symptoms, clinical exam, and confirmed by the results of a chromosome test. Due to various life-threatening medical problems, many infants with trisomy 13 do not survive past the first days or weeks of life.