Edward syndrome (trisomy 18, 47,XX+18 or 47,XY+18): numerical chromosomal abnormality,
autosomal trisomy.
Features are
Infants usually die in the first few weeks after birth
Delayed developmental milestones
Mental retardation
Prominent occiput
Short palpebral fissures
Narrow palatal arch
Micrognathia
Clenched hands with over-riding of fingers.
Short sternum
Umbilical or inguinal hernia
Congenital heart defects
Chromosome
Each chromosome is made up of condensed DNA which is tightly coiled many times around
proteins called histones and visible under metaphase stage.
Each chromosome has a constriction point called the centromere, which divides the chromosome
into two “arms.” The short arm of the chromosome is labeled the “p arm” and the long arm “q
arm.”
Depending on the position of centromere the chromosomes are classified morphologically into
o Metacentric- centromere is in the center of chromosome, where length of two arms is
equal. Chromosomes 1, 3, 16, 19
o Submetacentric- centromere is away from the center of chromosome, where one arm is
shorter than the other arm. Chromosomes 2, 4, 5, 6 to 12, 17, 18, X
o Acrocentric – centromere is towards one end of the chromosome, where one of the arms is
too short and the other arm is too long. Chromosomes 13, 14, 15, 20, 21, Y
Depending upon the length, position of centromere, bands, they are classified into 7 groups.
Group A- 1, 2, 3; group B- 4, 5; group C- 6-12, X; group D- 13, 14, 15; group E- 16, 17, 18; group F-
19, 20; group G- 21, 22, Y
autosomal trisomy.
Features are
Infants usually die in the first few weeks after birth
Delayed developmental milestones
Mental retardation
Prominent occiput
Short palpebral fissures
Narrow palatal arch
Micrognathia
Clenched hands with over-riding of fingers.
Short sternum
Umbilical or inguinal hernia
Congenital heart defects
Chromosome
Each chromosome is made up of condensed DNA which is tightly coiled many times around
proteins called histones and visible under metaphase stage.
Each chromosome has a constriction point called the centromere, which divides the chromosome
into two “arms.” The short arm of the chromosome is labeled the “p arm” and the long arm “q
arm.”
Depending on the position of centromere the chromosomes are classified morphologically into
o Metacentric- centromere is in the center of chromosome, where length of two arms is
equal. Chromosomes 1, 3, 16, 19
o Submetacentric- centromere is away from the center of chromosome, where one arm is
shorter than the other arm. Chromosomes 2, 4, 5, 6 to 12, 17, 18, X
o Acrocentric – centromere is towards one end of the chromosome, where one of the arms is
too short and the other arm is too long. Chromosomes 13, 14, 15, 20, 21, Y
Depending upon the length, position of centromere, bands, they are classified into 7 groups.
Group A- 1, 2, 3; group B- 4, 5; group C- 6-12, X; group D- 13, 14, 15; group E- 16, 17, 18; group F-
19, 20; group G- 21, 22, Y
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