Molecular identification of a partial hydatidiform mole

Molecular diagnosis of gestational trophoblastic disease

Gestational trophoblastic disease consists of well-defined diagnostic entities of proliferative disorder of the placenta, of which hydatidiform moles are common lesions. Even with available ancillary studies, including ploidy and immunohistochemistry analyses, histological diagnosis of molar pregnancies can be challenging in a significant percentage of the cases. Reliable diagnostic approaches with improved sensitivity and specificity are highly desirable. Recently, PCR-based short tandem repeat DNA genotyping has emerged as a powerful diagnostic measure in the workup of gestational trophoblastic disorders, particularly hydatidiform moles.

Genotypic analysis of hydatidiform mole: an accurate and practical method of diagnosis

Molar gestations are defined at the genetic level by their unique parental chromosomal compositions. Their diagnosis, however, currently relies largely on histologic features and on the occasional support of ancillary immunohistochemical and DNA ploidy analyses. We sought to validate DNA genotyping for the routine diagnosis and subtyping of hydatidiform moles (HMs) by analyzing 52 cases of molar pregnancy and their morphologic mimics. DNA was extracted from microdissected chorionic villi and paired maternal endometrial tissue from unstained paraffin sections and analyzed by AmpFlSTR Identifiler PCR Amplification system (Applied Biosystems, Inc). DNA genotyping was informative in all cases with input template DNA amounts ranging from 1.5 to 2.5 ng. Among 38 cases of HMs confirmed by DNA genotyping, there were 26 complete moles with diandric paternal-only genomes (24 homozygous and 2 heterozygous) and 12 partial moles with diandric, monogynic genomes (11 heterozygous and 1 homozygous). All nonmolar cases, including 10 cases of mimics of HM, demonstrated a balanced, biallelic profile of both maternal and paternal origin. Our study demonstrates the applicability of DNA genotyping, the molecular approach for the diagnosis, and subtyping of molar pregnancy, to the daily clinical practice.

Metastatic trophoblastic disease after an initial diagnosis of partial hydatidiform mole: genotyping and chromosome in situ hybridization analysis

BACKGROUND

Hydatidiform mole (HM) is classified into partial (PHM) and complete (CHM) subtypes according to histopathologic and genetic criteria. Traditionally, it is believed that PHM carries a better prognosis and rarely develops metastasis. However, making a distinction between PHM and CHM using histologic criteria alone may be difficult.

METHODS

The authors used fluorescent microsatellite genotyping following laser-capture microdissection and chromosome in situ hybridization (CISH) to perform a genetic analysis of six patients with histologically diagnosed PHM who subsequently developed metastatic gestational trophoblastic neoplasia.

RESULTS

Patients ranged in age from 25 years to 44 years (mean, 33.2 years). The gestational age of the molar pregnancies varied from 6 weeks to 20 weeks. All six patients had pulmonary metastases, with additional liver metastasis in two patients. Among the six patients with histologically diagnosed PHM, it was found that four patients had a diploid karyotype and no maternal alleles; thus, their neoplasms actually were CHM. Maternal genome was detected in the remaining two patients consistent with a biparental origin, and these patients had a triploid karyotype. CISH findings in all patients correlated with the genotyping findings. Triploid HM had maternally derived alleles, whereas diploid HMs were purely androgenetic.

CONCLUSIONS

In the current study, which may be the largest series of genetically analyzed metastatic PHMs to date, the difficulty of histologic distinction between PHM and CHM was confirmed. Molecular analysis may help to refine the classification of HM. Although the current findings support the belief that most aggressive trophoblastic diseases are derived from CHM, a small number of PHMs do progress to metastatic disease. Thus, the current study reaffirmed that all patients with HM should be followed closely irrespective of histologic subclassification.

Analysis of gestational trophoblastic disease by genotyping and chromosome in situ hybridization

Hydatidiform mole is classified into partial and complete subtypes according to histopathological and genetic criteria. Distinction between the two by histology alone may be difficult. Genetically, a complete mole is diploid without maternal contribution, whereas a partial mole is triploid with a maternal chromosome complement. To assess the accuracy of histological diagnosis by correlating with the genetic composition, we performed fluorescent microsatellite genotyping to detect the presence or absence of maternal genome in a hydatidiform mole and carried out chromosome in situ hybridization to analyze the ploidy. For genotyping analysis, paraffin sections of 36 complete and nine partial moles, diagnosed according to histological criteria, were microdissected and DNA was separately extracted from the decidua and molar villi. Six pairs of primers that flank polymorphic microsatellite repeat sequences on five different chromosomes were used. In all, 34 cases, including 31 complete moles and three partial moles diagnosed histologically, showed no maternal contribution by genotyping; thus these could be genetically considered as complete mole. The other 11 cases (five complete moles and six partial moles previously diagnosed by histology) showed the presence of maternal contribution and were genetically diagnosed as partial moles. The genotyping results correlated with histological evaluation in 88% (37/45) of hydatidiform mole and correlated with chromosome in situ hybridization findings in all the cases, that is, triploid hydatidiform moles had maternal-derived alleles, while diploid hydatidiform moles were purely androgenetic. Compared with genetic diagnosis, histological evaluation was more reliable for the diagnosis of a complete mole (91%, 31/34) than that of a partial mole (55%, 6/11) (P=0.0033). Seven complete moles and three partial moles diagnosed genetically developed gestational trophoblastic neoplasia. To conclude, genotyping and chromosome in situ hybridization can provide reliable adjunct to histology for the classification of a hydatidiform mole, especially in cases with difficult histological evaluation and early gestational age. As a partial mole still carries a risk of developing gestational trophoblastic neoplasia, follow-up is considered necessary for both complete and partial moles.

Mutations in the gene encoding the alpha-subunit of the Gs protein in molar pregnancy

Molar pregnancy is a gestational trophoblastic disease associated with a trophoblastic proliferation and a protein synthesis alteration. It is characterized by the presence of hydatiform moles, which are fluid-filled cysts derived from the chorionic villi of the placenta. Recent studies have reported a reduced expression of several types of G proteins including Gsalpha in molar pregnancies suggesting alterations in G protein structure in hydatiform moles. To identify mutations that lead to Gsalpha deficiency, we isolated genomic DNA from hydatiform moles and used polymerase chain reaction to amplify all exons of the Gsalpha gene. Amplified Gsalpha gene fragments were analyzed by sequencing using the dideoxy chain termination method. Tissues obtained from three complete hydatiform moles and one partial hydatiform mole were examined. We have identified a heterozygous 8-bp deletion in exon 10 of the Gsalpha gene, in two complete hydatiform moles, that had evidence for a dysfunctional Gsalpha protein. This deletion produced a truncated protein. We have also identified a heterozygous polymorphism in exon 5 in two complete hydatiform moles, and a homozygous substitution (A-->G) in intron 5 of the Gsalpha gene in the other complete hydatiform mole; these two last types of mutations should not have any effects on protein activity.