Histopathological features of biparental complete hydatidiform moles in women with NLRP7 mutations

Molar pregnancies, characterized by hydropic change and trophoblast hyperplasia of chorionic villi, are usually sporadic. Second and third molar pregnancies can occur by chance but may be associated with a rare autosomal recessive condition, familial recurrent hydatidiform mole (FRHM). This condition, in which affected women have a predisposition to complete hydatidiform moles (CHM), is not usually diagnosed until women have experienced several CHM when a differential diagnosis is made by demonstrating the CHM are diploid and biparental (BiCHM) in contrast to sporadic CHM which are androgenetic (AnCHM). Our objective was to investigate whether these genetic differences might be reflected in identifiable phenotypic differences between BiCHM and AnCHM that could enable earlier diagnosis of FRHM.

Histopathological features were compared between 27 AnCHM from 17 individuals and 51 BiCHM from 20 families in whom a diagnosis of FRHM was confirmed by the presence of biallelic NLRP7 mutations or pathological variants.

A spectrum of morphological features was observed in BiCHM. As a group they show subtle, but consistent, histological differences from typical sporadic AnCHM, with less marked villous trophoblast hyperplasia, extravillous trophoblast fragments, stromal apoptotic debris, budding architecture, cisterns and trophoblastic inclusions. While there are some BiCHM that individually show atypical histological features, the majority are indistinguishable from typical sporadic AnCHM.

The majority of cases of FRHM cannot be distinguished from sporadic AnCHM on the basis of histopathological features alone. In a minority of cases CHM may demonstrate 'atypical' features that raise the possibility of underlying BiCHM requiring further investigation.