Physical mapping of the uterine leiomyoma t(12;14)(q13-15;q24.1) breakpoint on chromosome 14 between SPTB and D14S77

An update on clonality: what smooth muscle cell type makes up the atherosclerotic plaque?

Almost 50 years ago, Earl Benditt and his son John described the clonality of the atherosclerotic plaque. This led Benditt to propose that the atherosclerotic lesion was a smooth muscle neoplasm, similar to the leiomyomata seen in the uterus of most women. Although the observation of clonality has been confirmed many times, interest in the idea that atherosclerosis might be a form of neoplasia waned because of the clinical success of treatments for hyperlipemia and because animal models have made great progress in understanding how lipid accumulates in the plaque and may lead to plaque rupture. Four advances have made it important to reconsider Benditt's observations. First, we now know that clonality is a property of normal tissue development. Second, this is even true in the vessel wall, where we now know that formation of clonal patches in that wall is part of the development of smooth muscle cells that make up the tunica media of arteries. Third, we know that the intima, the "soil" for development of the human atherosclerotic lesion, develops before the fatty lesions appear. Fourth, while the cells comprising this intima have been called "smooth muscle cells", we do not have a clear definition of cell type nor do we know if the initial accumulation is clonal. As a result, Benditt's hypothesis needs to be revisited in terms of changes in how we define smooth muscle cells and the quite distinct developmental origins of the cells that comprise the muscular coats of all arterial walls. Finally, since clonality of the lesions is real, the obvious questions are do these human tumors precede the development of atherosclerosis, how do the clones develop, what cell type gives rise to the clones, and in what ways do the clones provide the soil for development and natural history of atherosclerosis?

Whole exome sequencing in a random sample of North American women with leiomyomas identifies MED12 mutations in majority of uterine leiomyomas

Uterine leiomyomas (uterine fibroids) arise from smooth muscle tissue in the majority of women by age 45. It is common for these clonal tumors to develop from multiple locations within the uterus, leading to a variety of symptoms such as pelvic pain, abnormal uterine bleeding, and infertility. We performed whole exome sequencing on genomic DNA from five pairs of leiomyomas and corresponding normal myometrium to determine genetic variations unique to leiomyomas. Whole exome sequencing revealed that the gene encoding transcription factor MED12 (Mediator complex subunit 12) harbored heterozygous missense mutations caused by single nucleotide variants in highly conserved codon 44 of exon 2 in two of five leiomyomas. Sanger re-sequencing of MED12 among these five leiomyomas confirmed the two single nucleotide variants and detected a 42 base-pair deletion within exon 2 of MED12 in a third leiomyoma. MED12 was sequenced in an additional 143 leiomyomas and 73 normal myometrial tissues. 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/insertion-deletions spanning the intron 1-exon 2 boundary which affected the splice acceptor site. Mutations were not detected in MED12 in normal myometrial tissue. MED12 mutations were equally distributed among karyotypically normal and abnormal uterine leiomyomas and were identified in leiomyomas from both black and white American women. Our studies show an association between MED12 mutations and leiomyomas in ethnically and racially diverse American women.

Incidence, aetiology and epidemiology of uterine fibroids

Uterine fibroids are the most common benign tumour of the female genital tract. However, their true prevalence is probably under-estimated, as the incidence at histology is more than double the clinical incidence. Recent longitudinal studies have estimated that the lifetime risk of fibroids in a woman over the age of 45 years is more than 60%, with incidence higher in blacks than in whites. The cause of fibroids remains unclear and their biology poorly understood. No single candidate gene has been detected for commonly occurring uterine fibroids. However, the occurrence of rare uterine fibroid syndromes, such as multiple cutaneous and uterine leiomyomatosis, has been traced to the gene that codes for the mitochondrial enzyme, fumarate hydratase. Cytogenetic abnormalities, particularly deletions of chromosome 7, which are found in up to 50% of fibroid specimens, seem to be secondary rather than primary events, and investigations into the role of tumour suppressor genes have yielded conflicting results. The key regulators of fibroid growth are ovarian steroids, both oestrogen and progestogen, growth factors and angiogenesis, and the process of apoptosis. Black race, heredity, nulliparity, obesity, polycystic ovary syndrome, diabetes and hypertension are associated with increased risk of fibroids, and there is emerging evidence that familial predisposition to fibroids is associated with a distinct pattern of clinical and molecular features compared with fibroids in families without this prevalence.

The genetic heterogeneity of uterine leiomyomata

Research investigating the genetics of UL has already been successful in gathering epidemiologic evidence for heritability, establishing the clonal and mosaic nature of these tumors, correlating genotypic and phenotypic characteristics, defining cytogenetic subgroups, and identifying specific genes involved in tumorigenesis. Although UL are known to be benign tumors, the impact they have on the lives of so many women can only be described as "malignant". For this reason, continuing the quest to ascertain the genes, functions, and mechanisms integral to UL development is absolutely imperative. Genetic tests for personalized medical management of women with fibroids is at the threshold for providing the most appropriate treatments (Fig. 3), and combined with developing less invasive therapies portends a brighter future for a major health problem for women.

hREC2, a RAD51-like gene, is disrupted by t(12;14) (q15;q24.1) in a uterine leiomyoma

A balanced translocation between chromosomes 12 and 14 is commonly seen in uterine leiomyoma (UL). We have previously cloned and characterized a 2 Mb segment of human chromosomal subband 14q24.1, and have shown that the t(12;14)(q15;q24.1) breakpoints from several ULs map within this region. Exon trapping of DNA clones spanning one such breakpoint revealed coding sequences from hREC2, a gene that shows significant amino acid sequence identity to the double-strand break repair enzyme RAD51. We report here that this breakpoint is located within a 19 kb intron of the hREC2 gene and that the translocation results in the premature truncation of the major hREC2 transcript. Mapping and sequence analyses show that alternative transcripts of the hREC2 gene, including novel isoforms identified in testis and uterus, are not interrupted by the translocation.

Genomic and functional map of the chromosome 14 t(12;14) breakpoint cluster region in uterine leiomyoma

A translocation involving chromosomes 12 and 14 [t(12;14)(q15;24.1)] is commonly seen in benign smooth muscle tumor as uterine leiomyoma (UL). A contig of P1-derived artificial chromosome and bacterial artificial chromosome clones on chromosome 14, encompassing a t(12;14) breakpoint cluster region (BCR) in UL, was generated principally using the recently developed HAPPY map of chromosome 14 as a framework (P. H. Dear et al., 1998, Genomics 48: 232-241). Three UL t(12;14) breakpoints have been localized within this contig, showing that a BCR of at least 400 kb exists on chromosome 14. Other studies of tumors with t(12;14) rearrangements similarly show breakpoints within a 475-kb multiple aberration region on chromosome 12. Thus t(12;14) is an example of a translocation in which the breakpoints are located within a BCR on both chromosome 12 and chromosome 14, justifying the identification of expressed sequences that are altered in these BCR regions. A total of four expressed sequences were identified in the BCR on chromosome 14. Two of these were novel cDNAs (D14S1460E and D14S1461E). The chromosome 14 cDNAs were expressed in multiple adult tissues. The identification of a large breakpoint cluster region on chromosome 14 suggests that translocations in this region mediate their effects at a distance and also that elements that predispose this region to recurrent chromosomal translocation may be widely distributed.

Cloning of a breakpoint cluster region on chromosome 14 in uterine leiomyoma

A recurrent reciprocal chromosomal translocation, t(12;14)(q15;q24) is frequently observed in uterine leiomyoma. Chromosome 12 breakpoints have been shown to occur in a region of approximately 150 kb that contains the gene for a high mobility group protein (HMGI-C). The breakpoint region on chromosome 14 has not been precisely defined. We have generated a contig of overlapping yeast artificial chromosome (YAC) clones approximately 3 Mb in size. Fluorescence in situ hybridization (FISH) analysis showed that this contig spanned the t(12;14) breakpoints in three uterine leiomyomas and that the breakpoints in these tumors occurred within a 1 Mb region. A 30 kb cosmid spanning one of the breakpoints was isolated to set the stage for identifying regions on chromosome 14 that may cause this region to be a preferential site for chromosomal translocation.

Precise mapping of t(12;14) leiomyoma breakpoint on chromosome 14 between D14S298 and D14S540

Uterine leiomyoma is a common tumor of smooth muscle cell origin often characterized by the presence of a balanced t(12;14)(q13-15;q24.1) chromosomal translocation. This breakpoint on chromosome 14 had previously been placed between the markers SPTB and D14S77, a region estimated to span 7 cM. In this study we have used a meiotic breakpoint mapping panel to construct a high resolution genetic map of this interval. Markers that mapped within this interval were used to analyze DNA from a somatic cell hybrid containing the t(12;14) translocated chromosome. The results of this analysis localize the t(12;14) breakpoint on chromosome 14 between D14S298 and D14S540, between which no meiotic recombination was detected. This sets the stage for identifying the gene(s) disrupted by the chromosomal translocation by defining the markers that flank the translocation breakpoint.