Familial/bilateral and sporadic testicular germ cell tumors show frequent genetic changes at loci with suggestive linkage evidence

Familial Occurrence of a Severe Phenotype of Central Serous Chorioretinopathy in Two Brothers

We report the familial occurrence of a severe phenotype of central serous chorioretinopathy (CSC). A 62-year-old man was referred to our institute to treat a macular lesion in his right eye. Best-corrected visual acuity (BCVA) in his right eye was 0.05 (decimal format). On the initial visit, swept-source optical coherence tomography (SS-OCT) demonstrated subretinal hyperreflective material (SHRM) and subretinal fluid involving the central macula in the right eye and a descending tract on fundus autofluorescence (FAF) in the left eye, and fluorescein angiography revealed focal leakage corresponding to choroidal vascular hyperpermeability (CVH) on indocyanine green angiography (ICGA) of the right eye. He received photodynamic therapy (PDT) for the right eye and exudation disappeared. His 66-year-old elder brother had a medical history of CSC in both eyes and had received treatment at our hospital at 61 years old. On the initial presentation, ICGA showed multiple CVH in both eyes, and FAF showed hypofluorescence corresponding to retinal pigment epithelium (RPE) tears and RPE atrophy in both eyes. Bullous retinal detachment (RD) developed inferiorly in both eyes, and a vitrectomy was performed for the right eye to repair RD. The baseline BCVA was 0.3 in both eyes. Two years after the initial visit, recurrent serous RD developed in his left eye, and multiple PDT sessions were performed during the six-year follow-up. A severe phenotype of CSC may be associated with a genetic background.

DISTINCT CHARACTERISTICS OF SIMPLE VERSUS COMPLEX CENTRAL SEROUS CHORIORETINOPATHY

PURPOSE

To compare the clinical and genetic characteristics of simple and complex central serous chorioretinopathy using central serous chorioretinopathy international group criteria.

METHODS

Patients with idiopathic central serous chorioretinopathy were included. Depending on the presence or absence of retinal pigment alterations greater than 2-disc areas in either eye, patients were classified into complex or simple types. Demographic factors and clinical findings were compared between groups. CFH variants, including rs800292 and rs1329428, were genotyped using TaqMan technology.

RESULTS

A total of 319 consecutive patients were evaluated at the initial presentation. Of them, 53 (16.6%) had the complex type. The complex type was exclusively seen in men (100% vs. 79.0%, P = 2.0 × 10 -4 ) and demonstrated a significantly higher proportion of bilateral involvement (75.5% vs. 17.7%, P = 6.2 × 10 -18 ) and descending tract(s) (83.0% vs. 0%, P = 1.2 × 10 -57 ) than the simple type. Increased choroidal thickness (425 ± 131 vs. 382 ± 110, P = 0.02) and decreased central retinal thickness (274 ± 151 vs. 337 ± 136, P = 2.9 × 10 -4 ) were observed for the complex versus simple type. The risk allele frequencies of both variants were significantly higher in the complex versus simple type (rs800292: 61.3% vs. 48.7%, P = 0.018; rs1329428: 65.1% vs. 54.3%, P = 0.04).

CONCLUSION

In this new classification system, the complex type has distinct genetic and clinical characteristics compared with the simple type.

Exome sequencing of bilateral testicular germ cell tumors suggests independent development lineages

Intratubular germ cell neoplasia, the precursor of testicular germ cell tumors (TGCTs), is hypothesized to arise during embryogenesis from developmentally arrested primordial germ cells (PGCs) or gonocytes. In early embryonal life, the PGCs migrate from the yolk sac to the dorsal body wall where the cell population separates before colonizing the genital ridges. However, whether the malignant transformation takes place before or after this separation is controversial. We have explored the somatic exome-wide mutational spectra of bilateral TGCT to provide novel insight into the in utero critical time frame of malignant transformation and TGCT pathogenesis. Exome sequencing was performed in five patients with bilateral TGCT (eight tumors), of these three patients in whom both tumors were available (six tumors) and two patients each with only one available tumor (two tumors). Selected loci were explored by Sanger sequencing in 71 patients with bilateral TGCT. From the exome-wide mutational spectra, no identical mutations in any of the three bilateral tumor pairs were identified. Exome sequencing of all eight tumors revealed 87 somatic non-synonymous mutations (median 10 per tumor; range 5-21), some in already known cancer genes such as CIITA, NEB, platelet-derived growth factor receptor α (PDGFRA), and WHSC1. SUPT6H was found recurrently mutated in two tumors. We suggest independent development lineages of bilateral TGCT. Thus, malignant transformation into intratubular germ cell neoplasia is likely to occur after the migration of PGCs. We reveal possible drivers of TGCT pathogenesis, such as mutated PDGFRA, potentially with therapeutic implications for TGCT patients.

Hiwi downregulation, mediated by shRNA, reduces the proliferation and migration of human hepatocellular carcinoma cells

The Piwi subfamily is one of two Argonaute family proteins, which are characterized by the presence of Piwi and Piwi‑Argonaute‑Zwille domains, and are well known for their role in RNA silencing. Hiwi, a human member of the Piwi subfamily, is restricted to the germ line, where it binds Piwi‑interacting RNAs and functions in stem cell self‑renewal and gametogenesis. Previous reports have indicated that abnormal Hiwi expression may be associated with a poor prognosis of numerous types of human cancer, including hepatocellular carcinoma (HCC). However, little is currently known about the oncogenic role of Hiwi in HCC. In the present study, it was confirmed that Hiwi is overexpressed at both the mRNA and protein level, in HCC specimens, as well as in MHCC97L and MHCC97H HCC cell lines. A lentivirus‑mediated small hairpin rna (shRNA) targeting Hiwi was constructed and used to infect MHCC97L and MHCC97H cells. Relative Hiwi mRNA and protein expression levels were determined by quantitative polymerase chain reaction and western blot analysis, respectively. Cell proliferation, migration and invasion were determined using cell count, scratch and Transwell assays, respectively. Hiwi mRNA and protein expression was significantly downregulated in HCC cells in response to transduction with the lentivirus‑mediated shRNA. Furthermore, the proliferative, migrative and invasive properties of the shRNA‑transduced cells were significantly decreased. Therefore, Hiwi downregulation mediated by shRNA, may reduce the proliferation and migration of HCC cells. These results indicate that Hiwi may have an important role in the progression of HCC and may be a target for anticancer therapy.

Role of complement factor H I62V and age-related maculopathy susceptibility 2 A69S variants in the clinical expression of polypoidal choroidal vasculopathy

PURPOSE

To investigate the role of complement factor H (CFH) I62V (rs800292) and age-related maculopathy susceptibility 2 (ARMS2) A69S (rs10490924) variants in the clinical characteristics of polypoidal choroidal vasculopathy (PCV).

DESIGN

Cross-sectional study.

PARTICIPANTS

A total of 226 Japanese patients with PCV in both eyes (44 cases) or in 1 eye (182 cases).

METHODS

Genotyping was performed in all cases for CFH I62V using TaqMan technology and for ARMS2 A69S by denaturing high-performance chromatography. The incidence of 5 characteristic funduscopic findings was studied, including serous retinal detachment, subretinal hemorrhage, serous pigment epithelial detachment (PED), hemorrhagic PED, and classic choroidal neovascularization (CNV).

MAIN OUTCOME MEASURES

The association of clinical phenotypes, including the incidence of each of 5 specific fundus findings, bilaterality of the disease, and age at onset, with variants of CFH I62V or ARMS2 A69S.

RESULTS

Although there was no association of CFH I62V variants with any of the phenotypes in PCV, at-risk variants of ARMS2 A69S were associated with higher incidences of subretinal hemorrhage, serous PED, and hemorrhagic PED. In particular, the at-risk allele homozygosity of ARMS2 A69S increased the likelihood for hemorrhagic PED by 12.4-fold compared with non-carriers of the allele (confidence interval, 1.60-95.1, P = 0.0001). However, the at-risk allele of ARMS2 A69S was associated with a lower incidence of serous retinal detachment (P = 0.0092). Classic CNV was not associated with either variant. The mean age at the onset of PCV was significantly younger (68.8 years) in those with homozygosity of the at-risk allele of ARMS2 A69S than in those with heterozygosity (71.6 years) or in non-carriers (72.6 years) (P = 0.026). Moreover, the at-risk allele frequencies of the ARMS2 A69S were significantly higher in bilateral cases than in unilateral cases (75.0% vs. 59.3%, P = 0.007).

CONCLUSIONS

ARMS2 A69S variants were significantly associated with hemorrhagic or subpigment epithelium lesions of PCV, and with earlier onset and bilateral involvement. The genotyping of ARMS2 A69S is more informative than that of CFH I62V in understanding the clinical features in patients with PCV.

Chromosome X modulates incidence of testicular germ cell tumors in Ter mice

Germ cell tumor development in humans has been proposed to be part of testicular dysgenesis syndrome (TDS), which manifests as undescended testes, sterility, hypospadias, and, in extreme cases, as germ cell tumors. Males of the Ter mouse strain show interesting parallels to TDS because they either lack germ cells and are sterile or develop testicular germ cell tumors. We found that these defects in Ter mice are due to mutational inactivation of the Dead-end (Dnd1) gene. Here we report that chromosome X modulates germ cell tumor development in Ter mice. We tested whether the X or the Y chromosome influences tumor incidence. We used chromosome substitution strains to generate two new mouse strains: 129-Ter/Ter that carry either a C57BL/6J (B6)-derived chromosome (Chr) X or Y. We found that Ter/Ter males with B6-Chr X, but not B6-Chr Y, showed a significant shift in propensity from testicular tumor development to sterile testes phenotype. Thus, our studies provide unambiguous evidence that genetic factors from Chr X modulate the incidence of germ cell tumors in mice with inactivated Dnd1.

The role of dead-end in germ-cell tumor development

Testicular germ-cell tumors occur in human males of all age groups, from infants to men over 50 years old. Most commonly, germ-cell tumors (generally known as testicular cancer) occur in young males between the ages of 15 to 35 years. The tumor tissues are usually histologically diverse, and testicular tumors that occur in the different age groups tend to be of specific histological subtypes. Most germ-cell tumors originate from primordial germ cells during embryonic development, although the progression and eventual detection of the disease occurs decades later in humans. Mouse strains spontaneously develop a specific subtype of testicular germ-cell tumors, the type I germ-cell tumors, and these tumors are similar to the germ-cell tumors (or teratomas) that occur in human infants. Some mouse strains, such as the 129-Ter strain, have extremely high germ-cell tumor incidences, making such strains ideal for genetic and biological studies of germ cell-tumor development. Here a brief overview of the recently identified genetic defect in the Ter strain, inactivation of the dead-end (Dnd1) gene, and the ongoing studies on Dnd1 to understand its role in germ-cell and germ cell-tumor development, are provided.

Repression of Vascular Endothelial Growth Factor Expression by the Zinc Finger Transcription Factor ZNF24

Vascular endothelial growth factor (VEGF) is a potent stimulator of angiogenesis. Although many positive regulators of VEGF have been identified, relatively little is known regarding the negative regulation of VEGF expression. We identified a zinc finger transcription factor, ZNF24, that may repress VEGF transcription. An inverse correlation between expression of VEGF and ZNF24 was observed in a series of independent studies. ZNF24 was up-regulated in angiogenic tumor nodules where VEGF expression is significantly decreased compared with preangiogenic nodules. In human breast carcinoma cells cultured under normoxic conditions, ZNF24 levels were significantly up-regulated whereas VEGF levels were low. In contrast, VEGF was significantly increased in hypoxic cells whereas ZNF24 was down-regulated. The same inverse correlation between ZNF24 and VEGF was also observed in 70% of matched cDNA pairs of normal and malignant tissues from human colon and breast biopsies. Overexpression of ZNF24 resulted in a significant down-regulation of VEGF, whereas silencing of ZNF24 with small interfering RNA led to increased VEGF expression. Cotransfection of ZNF24 and a VEGF promoter luciferase reporter construct in MDA-MB-231 cells resulted in a significant decrease in VEGF promoter activity. Taken together, these data suggest that ZNF24 is involved in negative regulation of VEGF and may represent a novel repressor of VEGF transcription.

Identification of a novel prostate cancer-associated tumor antigen

BACKGROUND

The identification of antigens that distinguish cancer cells from normal cells is of major importance for the definition of therapeutic targets in human malignancies. Using sera from cancer patients, we have previously reported on the identification of immunologically recognized proteins that belong to the family of cancer testis antigens (CTAs).

METHODS

A normal testicular cDNA library was screened with pooled allogeneic sera from patients with prostate cancer using a modified SEREX approach. Subsequently we have identified and characterized a novel antigen, T21, with an expression pattern similar to that of CTAs. mRNA expression of T21 was determined using a panel of whole tissues and prostate cell lines using Q-RT-PCR. For laser microdissection, fresh prostate cancer and benign tissue was obtained using our novel validated harvesting technique. Protein expression and cellular localization of T21 were assessed in prostate cell lines using Western blotting, confocal microscopy and flow cytometry.

RESULTS

T21 showed tissue-restricted mRNA expression in gastric, kidney and prostate cancers, and in normal testis and prostate tissues. Following laser microdissection, T21 was significantly over-expressed in malignant compared to benign prostatic epithelium. We have demonstrated expression of T21 at the protein level and confocal microscopy on PC3 cells probed with a T21-monospecific antibody revealed cytoplasmic localization of T21 protein.

CONCLUSIONS

The highly restricted expression pattern of T21 makes it an attractive vaccine target for prostate cancer. Several CTAs reportedly induce cytotoxic T-lymphocyte responses, therefore it is reasonable to assume that T21 will be a valuable target for cancer immunotherapy.

Expression of SpanX proteins in normal testes and in testicular germ cell tumours

We investigated the expression of the SpanX protein family in cells of normal testes and in testicular germ cell tumours, mainly seminomas and embryonal carcinomas, using an immunohistochemical approach. Most of the normal germ cells, belonging to spermatogonial and primary spermatocytic classes, showed a strong nuclear positivity. In contrast, post-meiotic germ cells showed diffused cytoplasmic and sometimes also perinuclear localization of the signal. The vast majority of cells were also positive in eight seminomas, six embryonal cell carcinomas and one teratocarcinoma. In all seminomas, nuclei were either exclusively or preferentially labelled; whereas, the nuclear signal intensity decreased in parallel with the appearance of some cytoplasmic staining in embryonal carcinomas. In conclusion, these data suggest that the SpanX protein family is not exclusively expressed post-meiotically and that seminomas and embryonal carcinomas may originate from SpanX-positive carcinoma-in-situ cell.

Testicular germ cell tumours: the paradigm of chemo-sensitive solid tumours

Testicular germ cell tumours (TGCTs) are the most frequent solid malignant tumour in men 20-40 years of age and the most frequent cause of death from solid tumours in this age group. Up to 50% of the patients suffer from metastatic disease at diagnosis. The majority of metastatic testicular cancer patients, in contrast to most other metastatic solid tumours, can be cured with highly effective cisplatin-based chemotherapy. From a genetic point of view, almost all TGCTs in contrast to solid tumours are characterised by the presence of wild type p53. High p53 expression levels are associated with elevated Mdm2 levels and a loss of p21(Waf1/Cip1) expression suggesting a changed functionality of p53. Expression levels of other proteins involved in the regulation of cell cycle progression indicate a deregulated G1-S phase checkpoint in TGCTs. After cisplatin-induced DNA damage, the increasing levels of p53 lead to the trans-activation of a number of genes but not of p21(Waf1/Cip1), preferentially directing TGCT cells into apoptosis or programmed cell death, both via the mitochondrial and the death receptor apoptosis pathways. The sensitivity of TGCTs to chemotherapeutic drugs may lay in the susceptibility of germ cells to apoptosis. Taken together, this provides TGCT as a tumour type model to investigate and understand the molecular determinants of chemotherapy sensitivity of solid tumours. This review aims to summarise the current knowledge on the biological basis of cisplatin-induced apoptosis and response to chemotherapy in TGCTs.

Exploring the functions of RNA interference pathway proteins: some functions are more RISCy than others?

PPD (PAZ Piwi domain) proteins and the Dicer family have been the subjects of intense study over the last 6 years. These proteins have well-established roles in RNAi (RNA interference), a process that relies on siRNAs (small interfering RNAs) or miRNAs (microRNAs) to mediate specificity. The development of techniques for applying RNAi as a laboratory tool and a molecular therapeutic technique has rapidly outpaced our understanding of the biology of this process. However, over the last 2 years, great strides have been made towards elucidating how PPD proteins and Dicer regulate gene-silencing at the pre- and post-transcriptional levels. In addition, evidence is beginning to emerge that suggests that these proteins have additional siRNA-independent roles as cell-cycle regulators. In the present review, we summarize the well-known roles of these two classes of proteins in gene-silencing pathways, as well as explore the evidence for novel roles of PPD and Dicer proteins.

Defining minimum genomic regions of imbalance involved in testicular germ cell tumors of adolescents and adults through genome wide microarray analysis of cDNA clones

Identifying changes in DNA copy number can pinpoint genes that may be involved in tumor development. Here we have defined the smallest overlapping regions of imbalance (SORI) in testicular germ cell tumors other than the 12p region, which has been previously investigated. Definition of the regions was achieved through comparative genomic hybridization (CGH) analysis of a 4559 cDNA clone microarray. A total of 14 SORI were identified, which involved at least five of the 11 samples analysed. Many of these refined regions were previously reported using chromosomal or allelic imbalance studies. The SORI included gain of material from the regions 4q12, 17q21.3, 22q11.23 and Xq22, and loss from 5q33, 11q12.1, 16q22.3 and 22q11. Comparison with parallel chromosomal CGH data supported involvement of most regions. The various SORI span between one and 20 genes and highlight potential oncogenes/tumor suppressor genes to be investigated further.

Familial primary mediastinal nonseminomatous germ-cell tumors

In this article, we describe the case of 4 brothers, 2 of which had primary mediastinal nonseminomatous germ cell tumors (PMNSGCT), while the other 2 had benign mediastinal disease. We discuss the relationship between these diseases of the mediastinum and the thymic microenvironment. Additionally, we suggest that a genetic predisposition for germ-cell tumors (GCT) may be involved since the parents were relatives.

Testicular, Other Genital, and Breast Cancers in First-Degree Relatives of Testicular Cancer Patients and Controls

Previous studies showed an increased prevalence of testicular cancer among fathers and brothers of testicular cancer patients. We examined whether testicular, other genital, and breast cancers aggregate in parents and siblings of testicular cancer patients in a population-based case-control study, including males, ages 15 to 69 years at diagnosis, with primary malignant tumors of the testes or extragonadal germ cell tumors. Controls were ascertained through the mandatory registries of residents and frequency matched to the cases by age and region of residence. In a face-to-face interview, 269 cases and 797 controls provided health-related information on parents and siblings. We calculated odds ratios (OR) and corresponding 95% confidence intervals (95% CI) based on the generalized estimating equations technique, adjusting for the matching variables and relatives' age. Three (1.1%) fathers and eight (3.2%) brothers of cases were affected with testicular cancer compared with four (0.5%) fathers and two (0.2%) brothers of controls. The OR (95% CI) of familial testicular cancer was 6.6 (2.35-18.77). Only nonseminoma patients had fathers with testicular cancer, whereas the affected brothers were all related to seminoma patients. Overall, we found an increased risk for genital other than testicular cancers (OR 2.5, 95% CI 1.43-4.43). For breast cancer, we detected an increased risk in sisters (OR 9.5, 95% CI 2.01-45.16, adjusted for age of study participant and age of sister) but not in mothers. Our findings support the hypothesis that testicular and other genital cancers have a common familial component that may be due to genetic and shared exogenous factors such as estrogen exposure during fetal development.

Chromosomes, genes, and development of testicular germ cell tumors

A literature review found 265 articles on testicular germ cell tumors (TGCTs) detailing the copy number of chromosomal regions and expression of 245 genes. An initial precursor stage, intratubular germ cell neoplasia (IGCN), is characterized by triploidization and an upregulation of KIT, ALPP, CCDN2, and ZNF354A, and a downregulation of CDKN2D. TGCT regularly have a series of chromosomal aberrations: a decrease in copy number at 4q21 approximately qter and 5q14 approximately qter; an increase at 7p21 approximately pter, 7q21 approximately q33, and 8q12 approximately q23 (especially high increase in seminoma); a decrease at 11p11 approximately p15 and 11q14 approximately q24; an increase at 12p11 approximately pter; a decrease at 13q14 approximately q31; an increase of 17q11 approximately q21 (only for nonseminoma); a decrease of 18q12 approximately qter; and an increase at 21q21 approximately qter, 22q11 approximately qter (only for seminoma), and Xq. Macroscopically overt TGCT is associated with a characteristic series of abnormalities in the retinoblastoma pathway including upregulation of cyclin D2 and p27 and downregulation of RB1 and the cyclin-dependent kinase inhibitors p16, p18, p19, and p21. TGCT thus has a synergistic pattern in gene expressions of the retinoblastoma pathway that is rare in other malignancies.

Bilateral germ-cell tumours: 22-year experience at the Institut Gustave Roussy

The aim of this study was to describe the incidence, clinical and histological characteristics, treatment and long-term follow-up of bilateral germ-cell tumours (BGCT) of the testis in order to determine in what respects they differ significantly from unilateral germ-cell tumours. In all, 31 patients with BGCT had metachronous tumours and 14 had synchronous tumours. Among the metachronous tumours, 61% occurred more than 5 years after the first tumour. The overall incidence of BGCT in patients with testicular germ-cell tumours (TGCT) was 1.9%. The incidence was 3.2% in patients presenting with a seminoma and 1.4 % in patients presenting with a nonseminomatous germ-cell tumour (NSGCT). Patients under 30 years of age at the time of the initial diagnosis had a higher incidence of bilateral tumours compared with older men. The outcome of BGCT was excellent. A high association was found between BGCT, sterility and suspected genetic risk factors for TGCT. These results argue against a systematic contralateral biopsy at diagnosis of first TGCT in all patients, but emphasise the importance of patient education and of the need to better identify patients at risk for a second TGCT. Therapeutic indications for synchronous BGCT, including conservative treatment, need to be better defined.

Genetic evidence for a novel human desmosomal cadherin, desmoglein 4

Desmosomes are essential adhesion structures in most epithelia that link the intermediate filament network of one cell to its neighbor, thereby forming a strong bond. The molecular components of desmosomes belong to the cadherin superfamily, the plakin family, and the armadillo repeat protein family. The desmosomal cadherins are calcium-dependent transmembrane adhesion molecules and comprise the desmogleins and desmocollins. To date, three human desmoglein isoforms have been characterized, namely desmogleins 1, 2, and 3 that are expressed in a tissue- and differentiation-specific manner. Here we have identified and characterized, at the genetic level, a novel human desmoglein cDNA sharing homology with desmogleins 1, 2, 3 and we name this desmoglein 4. The human desmoglein 4 cDNA (3.6 kb) contains an open reading frame of 3120 bp that encodes a precursor protein of 1040 amino acids. The predicted mature protein comprises 991 amino acids with a molecular weight of 107822 Da at pI 4.38. Human desmoglein 4 shares 41% identity with human desmoglein 1, 37% with human desmoglein 2, and 50% with human desmoglein 3. Analysis of the exon/intron organization of the human desmoglein 4 gene (DSG4) demonstrates that it is composed of 16 exons spanning approximately 37 kb of 18q12 and is situated between DSG1 and DSG3. We have demonstrated using RT-PCR on multiple tissue cDNA samples that desmoglein 4 has very specific tissue expression in salivary gland, testis, prostate, and skin.

The testicular germ cell tumour genome

Human testicular germ cell tumour (TGCT) of adolescents and young adults develop from precursor lesions called carcinoma in situ (CIS), which is believed to originate from diploid primordial germ cells during foetal life. CIS is initiated by an aneuploidisation event accompanied by extensive chromosome instability. The further transformation of CIS into invasive TGCT (seminomas and nonseminomas) is associated with increased copy number of chromosome arm 12p, most often seen as isochromosome 12p. Despite the morphological distinctions between seminomatous and nonseminomatous TGCTs, they have many of the same regional genomic disruptions, although frequencies may vary. However, the two histological subtypes have quite distinct epigenomes, which is further evident from their different gene expression patterns. CIS develops from cells with erased parental imprinting, and the seminoma genome is under-methylated compared to that of the nonseminoma genome. High throughput microarray technologies have already pinpointed several genes important to TGCT, and will further unravel secrets of how specific genes and pathways are regulated and deregulated throughout the different stages of TGCT tumourigenesis. In addition to acquiring new insights into the molecular mechanisms of TGCT development, understanding the TGCT genome will also provide clues to the genetics of human embryonic development and of chemotherapy response, as TGCT is a good model system to both.

Frequent promoter hypermethylation of the O6-Methylguanine-DNA Methyltransferase (MGMT) gene in testicular cancer

Testicular germ cell tumours are classified into two major histological subgroups, seminomas and nonseminomas. All tumours display several recurrent chromosomal aberrations, but few target genes have been identified. Previous studies have shown that genome-wide hypermethylation of CpG islands is significantly more prevalent in nonseminomas than in seminomas. We have studied two potential target genes in testicular cancer. A series of 70 tumours were analysed for methylation of CpG sites in the O(6)-methylguanine-DNA methyltransferase (MGMT) gene promoter, and in exon 1alpha of the cyclin-dependent kinase inhibitor 2A gene (CDKN2A). In addition, eight microsatellite markers within and flanking these genes at chromosome arms 10q and 9p, respectively, were analysed for allelic imbalances. Allele alterations were frequently seen at 9p loci (47 out of 70, 67%), but none of the tumours (none out of 55) showed methylation of CDKN2A. On the other hand, a high frequency of MGMT promoter methylation (32 out of 69, 46%) was found, as well as allelic imbalances at 10q markers (50 out of 70, 71%). A significantly higher methylation frequency was found in nonseminomas (24 out of 35, 69%) compared to seminomas (eight out of 33, 24%) (P=0.0003, Fisher's exact test). Immunohistochemical analysis of the MGMT protein in a subgroup (n=20) of the testicular tumours supported the hypothesis of gene silencing being the functional consequence of the promoter methylation. In summary, our data suggest that inactivation of MGMT contributes to development of nonseminomatous testicular cancer.

Testicular carcinoma and HLA Class II genes

BACKGROUND

The association with histocompatibility antigens (HLA), in particular Class II genes (DQB1, DRB1), has recently been suggested to be one of the genetic factors involved in testicular germ cell tumor (TGCT) development. The current study, which uses genotyping of microsatellite markers, was designed to replicate previous associations.

METHODS

In 151 patients, along with controls comprising parents or spouses, the HLA region (particularly Class II) on chromosome 6p21 was genotyped for a set of 15 closely linked microsatellite markers.

RESULTS

In both patients and controls, strong linkage disequilibrium was observed in the genotyped region, indicating that similar haplotypes are likely to be identical by descent. However, association analysis and the transmission disequilibrium test did not show significant results. Haplotype sharing statistics, a haplotype method that derives extra information from phase and single marker tests, did not show differences in haplotype sharing between patients and controls.

CONCLUSION

The current genotyping study did not confirm the previously reported association between HLA Class II genes and TGCT. As the HLA alleles for which associations were reported are also prevalent in the Dutch populations, these associations are likely to be nonexistent or much weaker than previously reported.