Cytogenetic Nomenclature & abbreviations

“Cytogenetics traditionally refers to the study of chromosomes by microscopy following the application of banding techniques, permitting identification of abnormalities of chromosome number, loss or gain of chromosomal material or positional changes”. Standardized nomenclature is critical for the accurate and consistent description of genomic changes as identified by karyotyping, fluorescence in situ hybridization and microarray. The International System for Human Cytogenomic Nomenclature (ISCN) is the central reference for the description of karyotyping, FISH, and microarray results, and provides rules for describing cytogenetic and molecular cytogenetic findings in laboratory reports. These laboratory reports are documents to the referring clinician, and should be clear, accurate and contain all information relevant for good interpretation of the cytogenetic findings.

1. Cytogenetic Nomenclature & Abbreviations By: Manahil khanum (B-MMG-17-42)

2. Cytogenetics Cytogenetics traditionally refers to the study of chromosomes by microscopy following the application of banding techniques, permitting identification of abnormalities of chromosome number, loss or gain of chromosomal material or positional changes.

3. THE NORMAL HUMAN KARYOTYPE p (petit) pter for the short arm and q qter for the long arm The International System for Human Cytogenetic Nomenclature (ISCN) was established in 1978. A normal human karyotype  contains 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes, generally arranged in order from largest to smallest. A karyotype can be used to visualize abnormalities in the chromosomes, such as an incorrect number of chromosomes, deletions, insertions, or translocations of DNA. The main landmarks of each chromosome are the centromere , cen , Satellite chromosomes  or SAT- chromosomes  are  chromosomes  that contain secondary constructs that serve as identifying markers. In addition to the centromere , one or more secondary constrictions can be observed in some  chromosomes  at metaphase. These  chromosomes  are called  satellite chromosomes . Any subdivision of a  chromosome  along its length. Chromosomal regions  include parts that are not part of the chromatin .Each region is further subdivided into bands and subands .

4. Bands & Sub Bands Chromosome  banding refers to alternating light and dark regions along the length of a  chromosome , produced after staining with a dye. A  band  is defined as the part of a  chromosome  that is clearly distinguishable from its adjacent segments by appearing darker or lighter with the use of one or more banding techniques. To clarify more the study of chromosome(position) Sub bands which are Sub divisions of bands are used. The cytogenetic bands are labeled p1, p2, p3, q1, q2, q3, etc., counting from the centromere out toward the telomeres. ... The sub-bands are also numbered from the centromere out toward the telomere.

5. How to Write Karyotypes Place a comma behind the first number. This is followed by identifying the sex chromosomes XX (female) or XY (male), write the appropriate sex. ( eg . 46,XX is female; 46, XY is male) Match the homologous chromosomes according to their size (descending order), centromere position and banding pattern. These three indicators will serve as a guide for properly matching the chromosomes creating your karyotype .. Write the total number of chromosomes for the test subject used (humans, dogs, pigs. etc. have different numbers of chromosomes). For people the number is 46, unless there are defective or additional chromosomes . A dd a plus or minus sign to the affected chromosome number for an abnormal karyotype , placing it behind a comma after the sex chromosome. The plus or minus sign signifies there is an added chromosome or missing chromosome (or a chromosome can be missing parts). For a male with an extra number 19 chromosome, the karyotype would be displayed as 47,XY,+19 as one chromosome was added to the total of 46; +19 is displayed at the end, identifying the additional chromosome.

6. How to Write Karyotypes Make another set of parenthesis directly after the first set of parenthesis. Within the parenthesis write a 'p' for the short arm of the chromosome or a 'q' for the long arm. This establishes which part (or arm) of the chromosome is missing. Add (or subtract) one to or from your total number in the first set of numbers for the abnormal karyotype . If there is only a part of the chromosome missing or added, the first set of total numbers will not be affected. Write 'del' when a chromosome is missing only parts. Del is written in a third set of numbers (replacing the plus and minus sign and affected chromosome) before a set of parenthesis. Within the parenthesis write the number of the affected chromosome incurring change. Find the 'break point' of the change indicating the chromosome in the second set of parenthesis. Put the p or q before the break point chromosome. Example, a female missing the bottom arm of a chromosome 5 would be expressed as 46,XX, del(5)(q16). 'Del' says the chromosome is missing something. (5) delineates the origin of the problem. 'Q' indicates the missing part of the chromosome is the long arm. '16' identifies the break point chromosome .

7. Cytogenetic Nomenclature Abbreviation Meaning Example Condition 46, XX Normal Female Karyotype 46, XY Normal Male Karyotype cen Centromere del Deletion 46,XX,del(5p) Female with cri du chat syndrome due to deletion of part of short arm of one chromosome 5 der derivative chromosome der (1) Translocation chromosome derived from chromosome 1 and containing the centromere of chromosome 1 dic dicentric chromosome dic (X;Y) Translocation chromosome containing centromeres from both the X and the Y chromosomes dup Duplication fra fragile site 46, Y fag(X)(q27.3) Male with fragile X chromosome i isochromosome 46,X,i( Xq ) Female with isochromosome fro the long arm of the X chromosome. ins Insertion inv Inversion inv(3)(p25:q21) Pericentric inversion of chromosome 3 mar marker chromosome 47,XX,+mar Female with an extra unidentified chromosome.

8. mat maternal origin 47,XY,der(1)mat male with additional der(1) translocation chromosome inherited from his mother. p short arm of chromosome pat paternal origin q long arm of chromosome r ring chromosome 46,X,r(X) Female with ring X chromosome rcp reciprocal  translocation rob Robertsonian translocation t Translocation 46,XX,t(2;8)(q21;p13) Female with balanced translocation between chromosome 2 and chromosome 8, with breaks in 2q21 and 8p13 ter Terminus 46, X,Xq-(pter-->q21:) Female with partial deletion of the long arm from Xq21 to Xqter (nomenclature shows the portion of the chromosome that is present) + gain of 47,XX,+21 Female with trisomy 21 - loss of 45,XX,-14,-21,+t(14q21q) Normal female carrier of a robertsonian translocation between the long arms of chromosomes 14 and 21; karyotype is missing a normal 14 and a normal 21 4p- Chromosome 4 with a on of the short arm  deleted. : Break 5qter -->5p15: deleted chromosome 5 in a patient with cri du chat syndrome, with a deletion breakpoint in band p15 :: break and join 2pter-->2q21::8p13-->8pter Description of der (2) portion of t(2,8) / Mosaicism 46,XX/47,XX,+8 Female with two populations of cells, a normal karyotype and one with trisomy 8 Cytogenetic Nomenclature

9. THANK YOU…