CHROMOSOMAL

ABNORMALITIES

What are chromosomal abnormalities?

• These alterations can be detected by studying the affected person´s karyotype.

• There are many types of chromosomal abnormalities. However, they can be organized into two basic groups:

▫ Numerical abnormalities:

▫ Structural abnormalities

Normal karyotype

• There are 46 chromosomes (23 homologous ones)

• Homologous chromosomes are evenly banded)

Changes in the number of chromosomes of a karyotype.

Numerical abnormalities

• Monosomy: an individual is missing one of the chromosomes from a pair.

• Trisomy: an individual has three chromosomes instead of a pair

Numerical abnormalities. MONOSOMY

• Turner´s syndrome (XO):

▫ Disorder affecting women

▫ An only X chromosome in pair 23 (sex chromosomes)

▫ Clinical symptoms:

Sterility and underdeveloped genitals

Short height

▫ Frequency: 1 / 3300 birhts

• Turner´s syndrome (XO):

Numerical abnormalities. TRISOMY

• Klinefelter´s syndrome (XXY):

▫ Disorder affecting men

▫ Two X chromosomes and one Y chromosome in pair23 (sex chromosomes)

▫ Clinical symptoms:

Small genitals and sterility in some cases

Mild learning disabilities

▫ Frequency: 1.4 / 1000 births

• Klinefelter´s syndrome (XXY):

Numerical abnormalities. TRISOMY

• Triple X syndrome (XXX) = super female

▫ Disorder affecting women

▫ Three X chromosomes in pair 23 (sex chromosomes)

▫ Clinical symptoms:

Mild learning disabilities

Delayed development of speech and motor skills

▫ Frequency: 1 / 1000 births

• Triple X syndrome (XXX):

Numerical abnormalities. TRISOMY

• XYY syndrome:

▫ Disorder affecting men

▫ One X chromosome and two YY in pair 23 (sex chromosomes)

▫ Clinical symptoms:

Skeleton malformations (very tall)

Moderate learning disabilities and aggressiveness

▫ Frequency: 1 / 2000 births

• XYY syndrome:

Numerical abnormalities. TRISOMY

• Down´s syndrome:

▫ Disorder affecting women or men (not sex-linked)

▫ Three chromosomes in pair 21

▫ Clinical symptoms:

Varying degrees of intellectual disability

Flat head syndrome (brachycephaly)

Unusually small chin, skin folds at the edge of the eyes, round face, shorter limbs.

Various problems with eyesight and heart.

▫ Frequency: 1.5 / 1000 births

• Down´s syndrome:

Numerical abnormalities. TRISOMY

• Edwards´s syndrome:

▫ Disorder affecting women and men (not sex-linked)

▫ Three chromosomes in pair 18

▫ Clinical symptoms:

Severe intellectual disability

Kidney and heart malformations

Arrested growth and abnormal development of limbs

Short neck and sternum

▫ Frequency: 1 / 6766 births

• Edwards´s syndrome:

Numerical abnormalities. TRISOMY

• Patau´s syndrome:

▫ disorder affecting women and men (not sex-linked)

▫ Three X chromosomse in pair 13

▫ Clinical symptoms:

Intellectual disability

Heart, genital, finger and brain malformations

Missing palate

Deformed feet

▫ Frequency: 1 / 4600 births

• Patau´s syndrome:

Changes located in the structure of every single chromosome

Structural abnormalities

• Deletions: A portion of the chromosome is missing or deleted.

Structural abnormalities

• Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material.

Structural abnormalities

• Translocations:A portion of one chromosome is transferred to another chromosome.

Structural abnormalities

• Inversions: A portion of the chromosome has broken off, turned upside down, and reattached. As a result, the genetic material is inverted.

References

• http://www.genome.gov/11508982#al-5

• http://www.dnaftb.org/#classical

• http://learn.genetics.utah.edu/content/disorders/chromosomal/

• Cabrera. A. et al. 2012. 4 ESO. Biology and Geology. Oxford Education