Autosomal Aneuploidy – Cytogenetic Abnormalities

Kok Siong Chen — Tue, 22 Dec 2009 14:20:31 +0000

Cytogenetic abnormalities are what I have learnt during my internship in Hospital Kuala Lumpur. Today, I’m going to introduce Autosomal Aneuploidy in this Cytogenetics and Cancer Research blog.

In Cytogenetics, the term aneuploidy refers to cytogenetic abnormalities in which all or part of one or more chromosomes is added or deleted. Autosomal aneuploidy is the abnormality that does not involve the sex chromosomes. Sometimes, the abnormalities can be either numerical or structural. Normally we only have pair of chromosomes which are structurally similar. Other than that, it can be recognized as abnormal. Those cytogenetic abnormalities can be present only in some cells which we called mosaicism or in all cells.

Meiotic Nondisjunction Causes Autosomal Aneuploidy

The origin of autosomal aneuploidy is because of meiotic nondisjunction. The meiotic nondisjunction is random for all autosomes except for chromosome 21. Chromosome 21 has shown the highest frequency of autosomal aneuploidy.

According to cytogenetic studies, the incidence of autosomal aneuploidy in spontaneous abortuses (die before birth) is much higher than incidences in newborns. So, what is the case for aneuploidy actually observed in spontaneous abortuses or liveborns? All trisomies for all autosomes have been reported in spontaneous abortuses. The fetal only can survive if and only if the trisomies are in mosaic form. However, there are still many exceptions for the trisomies 13, 18 and 21. Some of the foetus still can survive even though the trisomies 13, 18 or 21 are in nonmosaic form.

Why the frequencies of trisomy for each chromosome might be similar at the time of conception but differ greatly among abortuses and liveborns especially for trisomy 21? It can be explained by the devastating effect of chromosomal imbalance. Most of the autosomal aneuploidies are very deleterious and lethal in the pre-embryonic stage. As a result, those abnormalities are unrecognized and, therefore, unstudied spontaneous abortions.

Furthermore, the lethality of a particular autosomal aneuploidy is related to the gene content of the particular chromosome. Aneuploidies for the gene rich chromosomes are less likely to survive. However, the less gene rich chromosomes like chromosome 13, 18 and 21 are more likely to survive to term.

Anyway, we will just focus on those observed in liveborns for the autosomal aneuploidy in Cytogenetics. I will talk more details about the monosomies and trisomies in my future post. Stay tuned!

Autosomal Aneuploidy – Cytogenetic Abnormalities is a post from: Cytogenetics and Cancer Research

Cytogenetic Studies in Malignancy Cancer

Kok Siong Chen — Thu, 03 Dec 2009 13:56:12 +0000

I think I never mention about the relationship between cytogenetics and cancer research in this blog. Cytogenetic studies are proven that can assist to define the diagnosis and deliver clear prognostic differences in cancer. There are many cytogenetic studies of malignancy have been gone through and most of them are related to hematologic disorders. However, those studies constitute only small percentage of all cancer malignancies.

Clinical Value of Cytogenetic Studies in Malignancy Cancer

Recently, there has been a significant progress in knowledge of the recurrent abnormalities in many of solid tumors as well as hematologic malignancies. Consequently, the clinical value of cytogenetic studies in cancer malignancy has been appreciated after the cytogenetic studies of some solid tumors moving out of cancer research environment.

Apart from this, there would be little clinical value in doing cytogenetic studies in cancer malignancy if all the patients with a particular cancer died. The researchers only manage to probe the origins of cancer for those patients. However, after researching in all tumors type by using cytogenetic technique, the presence or absence of many of the genetic abnormalities found has been related to different responses to treatment. Since that, the genetic and cytogenetic studies start to be recognized as important and one of the best choices of treatment for a cancer patient.

Cytogenetic Studies Helps Diagnostic Investigation in Malignancy Cancer

Consequently, cytogenetic analysis of cancer malignancy is considered to provide rapid, accurate and specific results to aid the clinical professionals. This can help to choose the most appropriate type of treatment to the cancer patient in shorter time. However, John Swansbury stated that the diagnosis of a malignancy can be traumatic, and an accurate and early indication of every patient’s prognosis is valuable.

In conclusion, a cytogenetic study remains an essential part of diagnostic investigations of every patient with hematologic malignancy and certain solid tumors without denying the valuable contributions made by other genetic assays.

Reference: Methods in Molecular Biology, vol. 220: Cancer Cytogenetics: Methods and Protocols. Edited by: John Swansbury © Humana Press Inc., Totowa, NJ

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Cytogenetic Studies in Malignancy Cancer is a post from: Cytogenetics and Cancer Research

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