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Figure: Spread and stained chromosomal preparation
The human cell normally contains the entire genetic information in 46 chromosomes (22 pairs of autosomes (all chromosomes other than the sex chromosomes) and two sex chromosomes). The DNA during the majority of the cell cycle is loosely packed in coiled and bundled strands. Chromosome identification and analysis can only be done on the condensed structures as they appear in the cell division process (mitosis). For cells to divide, DNA undergoes replication, and then further condensation during the prometaphase and metaphase steps of the cell division process, followed by the separation of the two chromosome sets (anaphase), each going to a daughter cell being formed. In the laboratory, cells are stimulated to divide in the test tube in order to create cells in mitosis where the chromosomes can be visualized.
Chromosomal abnormalities such as, an extra or missing chromosome, deletions or additions to the normal structure of specific chromosomes, or translocations between two chromosomes have been identified and correlated with specific phenotypes of anatomical, developmental and physiological abnormalities. Roughly 10-15% of all patients submitted for such testing by infertility clinics have an abnormal chromosomal picture. While some are acquired by inheritance, the majority originate anew.
Chromosome abnormalities are a significant cause of recurrent miscarriage and/or infertility. After three miscarriages there is a 3-8% chance that one member of the couple carries a balanced chromosome rearrangement (i.e. translocation) that can become unbalanced in reproduction. These translocations may be responsible for either recurrent miscarriage or prolonged infertility. Chromosome analysis is recommended for those couples undergoing infertility evaluation, those with recurrent miscarriage, men with oligo-or azoospermia, women with primary amenorrhea, or those individuals with a family history of a chromosome abnormality or mental retardation. Chromosome analysis of products of conception (POC) is recommended for recurrent miscarriages as 50% of first trimester miscarriages are due to chromosome abnormalities. This analysis is helpful for the couple to discover the cause of miscarriages, to better calculate recurrence risks for chromosome abnormality, and to possibly preclude further evaluation of other causes of pregnancy loss.
Patients with normal results might further continue with additional diagnostic work-up with their physician. However those with abnormal analysis should consult a geneticist in order to understand better the prognosis for their attempts to procreate (chances of success in this process with or without ART (artificial reproductive technologies)) and the risks involved for both the mother and child. Counseling with a Board Certified Geneticist should follow every abnormal finding. The utility of further diagnostic work-up may be precluded in some specific cases of abnormal karyotype, and should also be discussed in the course of such counseling. Following below, are some of the more common aberrations related to infertility, retardation and recurrent pregnancy loss:
Turner's Syndrome: This is a genetically determined condition that is associated with the presence of only one complete X chromosome and no Y chromosome and that is characterized by a female phenotype with underdeveloped and infertile ovaries.
Trisomy: a cell with an extra chromosome. There are various types of trisomies depending on which chromosome is affected:
Kleinefelter Syndrome: a karyotype with XXY sex chromosome set, associated with azoospermia and male infertility.
Balanced translocations:Numerous translocations have been described that may be associated with infertility. The most common translocations are those between acrocentric chromosomes (Robertsonian translocations). Translocations including the sex chromosomes are also found.
The normal chromosomal analysis would show
46 XX for the female
46 XY for the male
0.5 - 1.0 cm of fetal tissues in 5 ml of culture mediaor saline solution.
Use 15 ml sterilized conical tubes
-shipped at room temperature. Collection time and day: Anytime
To visualize the chromosomal structure, peripheral blood lymphocytes are stimulated with phytohemaglutinin (PHA) for 2-3 days to induce mitosis. In the course of this cell division, the chromosomes condense and become visible in light microscopy. Cells are then burst open by hypotonic shock; the preparation is stained and visualized microscopically. The individual chromosomes are identified (by size, banding patterns and the location of the centromere), enumerated and then scanned visually for abnormal band pattern and size abnormalities. Additional techniques may be applied for more detailed analysis of specific chromosome regions.