*2.4.1 Chromosomal abnormalities observed in endometriotic cells, loss of heterozygosity*

For decades, it has been a challenge to obtain consistent results on genetic abnormalities in endometriosis cells. The information produced by conventional cytogenetic and karyotypic studies is limited. The culture of pure endometriotic cells is hampered by the mixture of epithelial and stromal cells in addition to the inflammatory infiltrate containing fibroblasts and histiocytic cells; in addition, there may be excessive growth of normal cells [24].

Despite the difficulties, cytogenetic analysis plays an important role in the understanding of endometriosis, being the only technique that has the capacity to identify new chromosomal translocations, monosomies, and trisomies in chromosomes 11, 16, and 17.

Somatic genetic changes have been detected, distributed along several chromosomes, including chromosome 9p, 11q, and 22q. There have been allelic imbalances in 82% of endometriotic lesions diagnosed simultaneously with ovarian carcinoma.

These genetic studies have the limitation of having an adequate amount of endometriosis tissue from the patient and a simile of normal tissue to be used as control tissue, and in turn they have been limited to evaluating specific areas of the genome (detect loss of part of a chromosomal arm). But even so, they have been sufficiently useful to define the importance, in the development of endometriosis, of the inactivation of one or more suppressor genes [24–28].

### *2.4.2 Genetic aberrations by FISH: fluorescent in situ and hybridization comparative genomic hybridization*

FISH is a technology that uses DNA probes labeled with a fluorophore to detect or confirm gene or chromosomal abnormalities that are generally beyond the resolution capability of routine cytogenetics. First, the DNA sample (metaphase chromosomes or interphase nuclei) is denatured, a process that separates the complementary strands of the double-stranded structure in the DNA double helix. To the denatured sample is then added the probe of interest, which will be associated to the DNA of the sample at the target site, in the process called hybridization, where a double helix is re-formed. The probe is covalently linked (labeled) with a fluorophore, which emits an observable signal through a fluorescence microscope; thus the DNA sample can be classified according to the presence or absence of the signal, which reveals the presence or absence of the target sequence in the chromosomal DNA.

Comparing the genetic analysis with the FISH analysis, we can see that the FISH, by not requiring endometriosis cell culture and avoiding the inconveniences of cellular heterogeneity, has been more effective in revealing clonal aberrations such as

**15**

*The Role of the Molecular Genetic Approach in the Pathogenesis of Endometriosis*

covered, 700 microRNAs, and the entire mitochondrial genome [38, 39].

tissues was 3.1 per injury, which is low compared to malignant tissues [21].

monosomy for chromosomes 16 and 17 and an increase in the number of cells with

The comparative genomic hybridization by arrays (CGH-a) allows to realize a molecular karyotype and detect alterations inferior to 10 Mb throughout the genome. The genomic DNA of the sample and a control sample are differentially labeled with fluorescent dyes and hybridized with the oligonucleotides. The results are analyzed using quantitative methods with analysis software to determine the number of copies. It will not detect low-level mosaicism, balanced translocations, inversions, or point mutations that may be responsible for the clinical phenotype. This microarray analysis uses approximately 180,000 oligonucleotides that cover the entire genome at an average resolution of 30 KB, 1714 genes with all the exons

Through CGH-a, primary endometriotic lesions have been examined for gains and/or chromosomal losses. The losses that predominated over the gains showed a grouping in certain chromosomal regions that suggests a recurrent non-random

The average number of alterations of the copy in our series of endometriotic

The most common regions of loss of genomic material have been located in 1p involving at least 1p32–36 (50%), 5p (33%), 6q (27%), 7p14-p22ter (22%), 16qter (22%), and 22q12.3-qter (50%) segments. The other less common changes in the number of copies included the loss involving the arms of chromosomes 9q (22%), 16q

Chromosome 1 deletions were particularly common in all types and stages of endometriosis tissues, including peritoneal implants, endometriomas, and umbilical nodules. The gains were found less frequently and were located on chromosomes 6q and 17q. Several novel regions located on chromosomes 1p, 6q, and 22q that could harbor single or multiple tumor suppressor genes involved in the pathogen-

Chromosomal instability in endometrial lesions is the alteration of the chromosomal constitution that takes place in diverse pathological conditions: fundamental characteristic of the neoplasic cells (the majority of the malignant and benign tumors), precancerous lesions (dysplasia, leukoplakia, and cystically altered tissues), chronic inflammatory conditions, infectious diseases, and diseases induced

Genomic instability is mainly caused by chromosomal alterations in nonneoplastic precursor lesions and mutation of the P53 gene, and in errors in DNA replication detected by the instability of microsatellites (deficiency in the repair

Endometriosis tissues present this instability, through the presence of chromosomal copies, numerical changes, chromosomal deletions, translocations, the presence of endomitosis, premature centromeric dislocations, and the presence of micronuclei. The loss of essential genes or even of whole chromosomes explains the high invasive potential of endometriotic cells. The genomic alterations (rearrangements) initiated can be a primary event that facilitates the initiation and dissemination of endometriosis. It is the alteration of the chromosomal constitution that takes place in diverse pathological conditions: fundamental characteristic of the neoplasic cells (the majority of the malignant and benign tumors), precancerous lesions (dysplasia, leukoplakia, and cystically altered tissues), chronic inflammatory conditions, infectious diseases, and diseases induced by viruses (herpes, HPV, EBV, etc.) [34–37].

*DOI: http://dx.doi.org/10.5772/intechopen.81598*

pattern of chromosomal alterations.

(22%), and 17q [21, 22, 24–29, 33].

by viruses (herpes, HPV, EBV, etc.).

mechanism of DNA mismatch) [34, 35].

esis of endometriosis have been identified [38, 39].

*2.4.3 Chromosomal instability in endometrial lesions*

trisomy 11 [29–33].

*The Role of the Molecular Genetic Approach in the Pathogenesis of Endometriosis DOI: http://dx.doi.org/10.5772/intechopen.81598*

monosomy for chromosomes 16 and 17 and an increase in the number of cells with trisomy 11 [29–33].

The comparative genomic hybridization by arrays (CGH-a) allows to realize a molecular karyotype and detect alterations inferior to 10 Mb throughout the genome. The genomic DNA of the sample and a control sample are differentially labeled with fluorescent dyes and hybridized with the oligonucleotides. The results are analyzed using quantitative methods with analysis software to determine the number of copies. It will not detect low-level mosaicism, balanced translocations, inversions, or point mutations that may be responsible for the clinical phenotype.

This microarray analysis uses approximately 180,000 oligonucleotides that cover the entire genome at an average resolution of 30 KB, 1714 genes with all the exons covered, 700 microRNAs, and the entire mitochondrial genome [38, 39].

Through CGH-a, primary endometriotic lesions have been examined for gains and/or chromosomal losses. The losses that predominated over the gains showed a grouping in certain chromosomal regions that suggests a recurrent non-random pattern of chromosomal alterations.

The average number of alterations of the copy in our series of endometriotic tissues was 3.1 per injury, which is low compared to malignant tissues [21].

The most common regions of loss of genomic material have been located in 1p involving at least 1p32–36 (50%), 5p (33%), 6q (27%), 7p14-p22ter (22%), 16qter (22%), and 22q12.3-qter (50%) segments. The other less common changes in the number of copies included the loss involving the arms of chromosomes 9q (22%), 16q (22%), and 17q [21, 22, 24–29, 33].

Chromosome 1 deletions were particularly common in all types and stages of endometriosis tissues, including peritoneal implants, endometriomas, and umbilical nodules. The gains were found less frequently and were located on chromosomes 6q and 17q. Several novel regions located on chromosomes 1p, 6q, and 22q that could harbor single or multiple tumor suppressor genes involved in the pathogenesis of endometriosis have been identified [38, 39].

#### *2.4.3 Chromosomal instability in endometrial lesions*

Chromosomal instability in endometrial lesions is the alteration of the chromosomal constitution that takes place in diverse pathological conditions: fundamental characteristic of the neoplasic cells (the majority of the malignant and benign tumors), precancerous lesions (dysplasia, leukoplakia, and cystically altered tissues), chronic inflammatory conditions, infectious diseases, and diseases induced by viruses (herpes, HPV, EBV, etc.).

Genomic instability is mainly caused by chromosomal alterations in nonneoplastic precursor lesions and mutation of the P53 gene, and in errors in DNA replication detected by the instability of microsatellites (deficiency in the repair mechanism of DNA mismatch) [34, 35].

Endometriosis tissues present this instability, through the presence of chromosomal copies, numerical changes, chromosomal deletions, translocations, the presence of endomitosis, premature centromeric dislocations, and the presence of micronuclei.

The loss of essential genes or even of whole chromosomes explains the high invasive potential of endometriotic cells. The genomic alterations (rearrangements) initiated can be a primary event that facilitates the initiation and dissemination of endometriosis. It is the alteration of the chromosomal constitution that takes place in diverse pathological conditions: fundamental characteristic of the neoplasic cells (the majority of the malignant and benign tumors), precancerous lesions (dysplasia, leukoplakia, and cystically altered tissues), chronic inflammatory conditions, infectious diseases, and diseases induced by viruses (herpes, HPV, EBV, etc.) [34–37].

*Molecular Bases of Endometriosis - The Integration Between Research and Clinical Practice*

*2.4.1 Chromosomal abnormalities observed in endometriotic cells, loss of* 

there may be excessive growth of normal cells [24].

of the inactivation of one or more suppressor genes [24–28].

*comparative genomic hybridization*

*2.4.2 Genetic aberrations by FISH: fluorescent in situ and hybridization* 

presence or absence of the target sequence in the chromosomal DNA.

For decades, it has been a challenge to obtain consistent results on genetic abnormalities in endometriosis cells. The information produced by conventional cytogenetic and karyotypic studies is limited. The culture of pure endometriotic cells is hampered by the mixture of epithelial and stromal cells in addition to the inflammatory infiltrate containing fibroblasts and histiocytic cells; in addition,

Despite the difficulties, cytogenetic analysis plays an important role in the understanding of endometriosis, being the only technique that has the capacity to identify new chromosomal translocations, monosomies, and trisomies in chromo-

Somatic genetic changes have been detected, distributed along several chromosomes, including chromosome 9p, 11q, and 22q. There have been allelic imbalances in 82% of endometriotic lesions diagnosed simultaneously with ovarian carcinoma. These genetic studies have the limitation of having an adequate amount of endometriosis tissue from the patient and a simile of normal tissue to be used as control tissue, and in turn they have been limited to evaluating specific areas of the genome (detect loss of part of a chromosomal arm). But even so, they have been sufficiently useful to define the importance, in the development of endometriosis,

FISH is a technology that uses DNA probes labeled with a fluorophore to detect or confirm gene or chromosomal abnormalities that are generally beyond the resolution capability of routine cytogenetics. First, the DNA sample (metaphase chromosomes or interphase nuclei) is denatured, a process that separates the complementary strands of the double-stranded structure in the DNA double helix. To the denatured sample is then added the probe of interest, which will be associated to the DNA of the sample at the target site, in the process called hybridization, where a double helix is re-formed. The probe is covalently linked (labeled) with a fluorophore, which emits an observable signal through a fluorescence microscope; thus the DNA sample can be classified according to the presence or absence of the signal, which reveals the

Comparing the genetic analysis with the FISH analysis, we can see that the FISH, by not requiring endometriosis cell culture and avoiding the inconveniences of cellular heterogeneity, has been more effective in revealing clonal aberrations such as

endometriosis cells.

population [21–23].

*heterozygosity*

somes 11, 16, and 17.

immunoreactive with the anti-progesterone receptor (PR) antibody which shows a brown nuclear stain produced by the diaminobenzidine colorimetric reaction. Less than 15% are immunoreactive with the anti-androgen receptor antibody. Cytokeratins such as vimentin were expressed in endometriotic stromal cells. Therefore, most of the phenotypic characteristics of the normal endometrium are conserved in the

The existence of genomic aberrations in the tissues of endometriosis is probably related to genes involved in the development of the disease. Most genetic changes occur as germ line defects that can result in a hereditary predisposition to the development of endometriosis with a genetic basis for endometriosis. The prevalence of the disease is higher in first-degree relatives of affected women than in the general

**14**
