Gynecologic Disorders With a Genetic Causation




INTRODUCTION



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Case 1: Ms. Kolthoff is a 27-year-old G0 P0, who was evaluated for accelerated growth and advanced bone age in high school. She is currently married without children. She does not use birth control and despite sexual intercourse approximately a few times a week for the past 2 years, she has not conceived. She complains of having to shave her upper lip as well as hair on her back and abdomen. Her menstrual cycles are irregular and she sometimes will not have one for several months. She has experienced acne for which she took over-the-counter lotions for treatment with partial success, and was also given a short course of antibiotics by her physician. She has been told she has polycystic ovarian syndrome, and presents with concerns about her fertility. Her family history is unremarkable. She has three sisters who do not have hirsutism, and all three have children. The physical exam was significant for short stature, shaved upper lip, acne-related facial scarring, and significant abdominal and back hirsutism. Her external genitalia appeared normal and the pelvic exam was unremarkable. A basal 17-hydroxyprogesterone measure was 1850 ng/dL, while an ACTH stimulation test showed a 17-hydroxyprogesterone rise to 5300 ng/dL. What additional tests and evaluation would you consider for Ms. Kolthoff?




Gynecologic disorders can be heritable, such as polycystic ovarian syndrome, or can be due to sporadic somatic mutations that arise in individual organs, such as uterine leiomyomas. To date gene mutations have been associated with common gynecologic disorders, such as leiomyomas, polycystic ovarian syndrome, endometriosis, and menstrual dysfunction. We also know that specific genomic regions regulate important reproductive landmarks, such as menarche and menopause. In the future, genomic medicine will play a significant role in understanding the causation of gynecologic disorders and guiding individual therapies.




LEIOMYOMAS



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Leiomyomas, or fibroids, are common tumors arising from the myometrial layer of the uterus. They are clinically diagnosed in 25% of women, and are often associated with dysmenorrhea, menorrhagia, infertility, and abdominal discomfort. Subclinical leiomyomas are extremely common, and by age 50 more than 80% of black and 70% of white women have leiomyomas. Family history, black race, age, nulliparity, and obesity are known risk factors for the development of clinically significant leiomyomas. Family aggregation and twin studies show that genes contribute significantly to the genesis of leiomyomas.1 Common leiomyomas are monoclonal in origin, and 40% have associated chromosome abnormalities. Cytogenetic aberrations commonly include deletions in 7q, trisomy of chromosome 12, and various translocations between chromosomes 12 and 14 involving the high-mobility group AT-hook 2 (HMGA2) gene at 12q15, which encodes a transcriptional regulator. Cytogenetic abnormalities are likely a reflection of general genomic instability, as is true for other tumors. Individuals may have leiomyomas either due to germline mutations (rare) or due to somatic mutations that arise only in the uterus (common).



Heterozygous (present on one allele) germline mutations in fumarate hydratase (FH) predispose individuals to a rare disorder known as hereditary cutaneous and uterine leiomyomatosis with renal carcinoma (OMIM 150800).2 This disorder follows the classic Knudson “two-hit” model, where affected individuals carry a mutation in one allele in all tissues, and a second mutation is acquired in affected tissues to cause leiomyomatosis and renal cancer. Fumarate hydratase acts, therefore, as a tumor suppressor gene. However, fumarate hydratase mutations are not the cause of common leiomyomas.



Genomewide association studies have identified several genomic locations that associate with leiomyomas. Three loci on chromosomes 10q24.33, 22q13.1, and 11p15.5 were associated with clinically significant uterine fibroids in Japanese women,3 and seven loci on chromosomes 10p11, 3p21, 2q37, 5p13, 11p15, 12q14, and 17q25 were associated with leiomyomas in Caucasian women.4 The fatty acid synthase gene (FASN) is located on 17q25 and overexpressed in leiomyomas as compared to normal myometrium. FASN has been implicated in progression of other tumors, and possibly may provide a biologic link to leiomyomatous growth, although mechanistic evidence for it is lacking. Overall, it remains unclear how these loci influence leiomyomatous growth.



Somatic mutations in the MED12 gene (mediator complex subunit 12; located on Xq13.1) are associated with common leiomyomas.5,6 These mutations are present only in leiomyomas, but not in the surrounding, normal myometrial tissues. MED12 mutations cluster in exon 2, and the mechanisms by which these mutations arise in the myometrium are not well understood. Overall, MED12 was mutated in 100/148 (67%) of the genotyped leiomyomas: 79/148 (53%) leiomyomas exhibited heterozygous missense single nucleotide variants, 17/148 (11%) leiomyomas exhibited heterozygous in-frame deletions/insertion-deletions, 2/148 (1%) leiomyomas exhibited intronic heterozygous single nucleotide variants affecting splicing, and 2/148 (1%) leiomyomas exhibited heterozygous deletions/insertiondeletions spanning the intron 1 to exon 2 boundary which affected the splice acceptor site. The most commonly observed nonsynonymous SNP was the c.131G>A heterozygous mutation causing a glycine to aspartic acid amino acid change. MED12 mutations were equally distributed among karyotypically normal and abnormal uterine leiomyomas and were identified in leiomyomas from both black and white American women. It is, therefore, likely that MED12 variants deregulate the cell cycle in the normal myometrium, resulting in abnormal growth, genomic instability, and karyotype abnormalities in a subset of leiomyomas. The karyotype abnormalities are, therefore, a consequence of MED12 mutations, rather than cause of uterine leiomyomas. MED12 is a 250 kilodalton (kDa) protein, which is part of a large complex of mediator proteins, and is involved in transcriptional regulation of RNA polymerase II complex. This complex is highly conserved among all eukaryotes, and is involved in both repression and activation of DNA transcription as well as chromatin remodeling. MED12 is located on the X chromosome, and naturally occurring random X chromosome inactivation allows gene expression from only one of the X chromosomes. The X chromosome that carries the MED12 mutation is expressed in leiomyomas, meaning that altered MED12 protein is produced and causes tumorigenesis. Not all leiomyomas carry MED12 mutations, and therefore other mechanisms exist that lead to leiomyoma formation.


Jan 12, 2019 | Posted by in OBSTETRICS | Comments Off on Gynecologic Disorders With a Genetic Causation
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