Medical Genetics - V. M. Zaporozhan 2005

Etiology of Hereditary Diseases
Types of Mutations Caused by Changes in Chromosome Number and Structure
Recording Normal and Altered Human Karyotypes

According to the international cytogenetic nomenclature (ISCN, 1995), a normal Human Karyotype

is written as follows: 46,XX for a normal female karyotype, and 46,XY for a normal male karyotype. The first two digits indicate the total number of Chromosomes in humans, followed by a comma and the sex chromosomes.

Karyotype in polyploidy: 69,XXX; 69,XXY for triploidy; 92,XXXX; 92,XXXY for tetraploidy.

Karyotype in monosomy: 45,X is the only viable monosomy in humans (Turner syndrome).

Karyotype in autosomal trisomies:

47,XX,+13 or 47,XY,+13 for trisomy 13 (Patau syndrome);

47,XX,+18 or 47,XY,+18 for trisomy 18 (Edwards syndrome);

47,XX,+21 or 47,XY,+21 for trisomy 21 (Down syndrome).

Karyotype in sex chromosome trisomies:

47,XXX for Triple X syndrome in females;

47,XYY for XYY syndrome in males;

47,XXY for Klinefelter syndrome.

Tetrasomies and pentasomies of the sex chromosomes:

48,XXXX for X tetrasomy;

49,XXXXX for X pentasomy;

48,XXXY; 49,XXXXY as variants of Klinefelter syndrome;

48,XYYY; 49,XYYYY as variants of Y-polysomy in males.

Karyotype in mosaicism:

46,XX/47,XX,+21 represents a female with mosaic Down syndrome; some Cells have a normal karyotype, while others exhibit trisomy 21;

45,X/46,XX represents mosaic Turner syndrome, where some cells have a normal karyotype (46,XX) and others show monosomy X (45,X).

Karyotype in Chromosomal aberrations

A system of Abbreviations is used to describe chromosomal aberrations. Some accepted symbols are presented in Table 2.5.