Webster's New World Medical Dictionary

trimethylaminuria
See 
fish-odor syndrome.
triple X
See 
XXX syndrome.
triploid
Having three full sets of chromosomes: 3
copies of each autosomal chromosome plus 3 sex
chromosomes. In humans, triploid is equal to 69
chromosomes.
triplo-X
See 
XXX syndrome.
trismus pseudocamptodactyly syndrome
See
Hecht syndrome.
trisomy
The presence of three copies of a chro-
mosome rather than the normal two. The most com-
mon trisomies in newborns are trisomy 13 (Patau
syndrome), trisomy 18 (Edwards syndrome), and
trisomy 21 (Down syndrome).
trisomy 13 syndrome
The presence of three
copies of chromosome 13, rather than the normal
two. Children with trisomy 13 syndrome are pro-
foundly mentally retarded and have multiple malfor-
mations, commonly including scalp defects,
hemangiomas (blood vessel malformations) of the
face and nape of the neck, cleft lip and palate, mal-
formations of the heart and abdominal organs, and
flexed fingers with extra digits. The majority of tri-
somy 13 babies die soon after birth or in infancy.
Also known as Patau syndrome.
trisomy 18 syndrome
The presence of three
copies of chromosome 18, rather than the normal
two. Children with trisomy 18 syndrome have multi-
ple malformations and mental retardation. They
characteristically have low birth weight, small head
(microcephaly), small jaw (micrognathia), malfor-
mations of the heart and kidneys, clenched fists with
abnormal finger positioning, and malformed feet.
The mental retardation is profound, and the IQ is
too low to even measure. Nineteen out of 20 chil-
dren with trisomy 18 syndrome die before their first
birthday. Also called Edwards syndrome.