Biparental origin of the chromosome set is required for a developing human being

Conception sometimes results in products that are not capable of developing into an embryo and fetus. This group, designated with the term gestational trophoblastic neoplasia, comprises the benign hydatidiform mole, the invasive mole (chorioadenoma destruens) and the frankly malignant variety, choriocarcinoma. Another type of atypical oocyte activation occurs in parthenogenesis. In the human, two types of tumors, dermoid cysts and teratomas, can result from this process. The authors of this paper aim to elucidate the mechanisms how these abnormal growths ensue and provide explanations why they cannot be regarded as human individuals or human beings. They conclude that it is not the exact number of chromosomes that is required for a form of human life to become a human being but rather the biparental origin of the chromosome set. It is obvious that, apart from the future perspectives of reproductive cloning, all forms of human life begin with conception. But does conception always result in a developing human being? The answer is certainly no. Careful studies in women attempting pregnancy have shown that implantation fails in about 30% of cases and in another 30%, human chorionic gonadotropin (hCG) can transiently be detected in the urine of women who would otherwise be unaware that they had conceived and miscarried (1). One could argue that there is a developing human being in these cases that simply failed to develop but in fact, most of these embryos have some type of chromosomal abnormalities that would impede their development to term. Conception sometimes results in a special form of tumors, which belong to the group designated with the term gestational trophoblastic neoplasia. This group comprises the benign hydatidiform mole (Figure 1), the invasive mole (chorioadenoma destruens) (Figure 2), and the frankly malignant variety, choriocarcinoma (Figure 3). What these tumors have in common is their origin: they are derived from cytotrophoblast and syncytiotrophoblast cells, which normally would form the outer layer of the early developing blastocyst, giving later rise to chorionic villi of the placenta. The majority of hydatidiform moles are »complete« moles, in which no traces of a developing embryo can be found. In about 95% of cases, cells of these tumors have a 46,XX karyotype, in which both X chromosomes are paternally derived (Figure 4). These cells result from fertilization of an oocyte by a single sperm in a way that the nucleus of the ERIK HAUZMAN ZSOLT CSAPÓ ZOLTÁN PAPP First Department of Obstetrics and Gynecology Semmelweis University Faculty of Medicine Baross u. 27. H–1088 Budapest Hungary Correspondence: Erik Hauzman First Department of Obstetrics and Gynecology Semmelweis University Faculty of Medicine Baross u. 27. H–1088 Budapest Hungary E-mail: [email protected]