Genomic imprinting is defined as the differential expression of a gene or chromosomal region according to the parental origin of inheritance. Both the maternal and paternal alleles are present, but while one is functionally active, the other is silenced (inactive) in somatic cells (Figure 1a). Genomic imprinting is reversible through successive generations. Inherited maternal and paternal “imprints” are erased during gametogenesis (gamete production) and new imprints established according to the sex of the parent. Genomic imprinting is an epigenetic phenomenon (not dependent on the DNA sequence itself, but rather on factors that regulate DNA activity). These factors include attachments of methyl groups to the DNA, which are set in the gamete and serve to distinguish the parental alleles in somatic cells post-fertilization.

It is estimated that as many as 10% of couples worldwide suffer from infertility or reduced fertility, and that in approximately half of these cases this results from defective spermatogenesis. In 60% of these infertile men, the failure to produce mature germ cells (i.e. azoospermia) or the formation of low numbers of sperm (i.e. oligozoospermia) can be ascribed a genetic aetiology. Few of the loci associated with male infertility have been mapped in humans; however, several genetic models of defective germ-cell development and differentiation have been described in mice. The schematic in Figure 1 summarizes the main features of spermatogenesis in humans.

To prepare for the presence of a fetus, the uterus undergoes a critical process termed decidualisation that, in mice and probably humans, is required for reproductive success. This process involves phenotypic changes in uterine stromal cells that enable them to support implantation and placental development. Accompanying this transformation is the recruitment of a specialised population of maternal immune cells. These cells, termed decidual leukocytes, are a significant presence, composing up to 70% of cells in the uterus throughout early pregnancy. At first glance, the recruitment of immune cells to the site of implantation seems at odds with maternal tolerance. However, the unique characteristics of decidual leukocytes, particularly with regard to their abundance and distinct composition, suggest that they participate in protecting fetal tissues from immune attack. Thus, the mechanisms that recruit decidual leukocytes to the uterine wall provide an important component to successful pregnancy.

Group B streptococci (GBS), Streptococcus agalactiae, are Gram-positive bacteria occurring in pairs and short chains. S. agalactiae was originally investigated as a frequent cause of bovine mastitis; before the widespread use of penicillin, it accounted for as much as 90% of all bovine mastitis. It was first isolated from parturient women in 1935. Since the 1970s, GBS have emerged as important human pathogens and have remained the major cause of bacterial diseases in newborns in the western world. In 1990, there were approximately 7600 neonatal cases of invasive GBS disease in the USA. Since then, intense intrapartum use of antibiotics has decreased the incidence of neonatal early-onset GBS disease, to 2200 cases in 1998. Babies can be exposed to GBS during labour and delivery, when they swallow or inhale the bacteria while passing through the birth canal of the colonized mothers. Babies can also be exposed in utero. GBS infection in infants causes sepsis and meningitis, which can result not only in illness and death but also in long-term disabilities such as hearing loss, impaired vision, developmental problems and cerebral palsy. The direct costs of neonatal disease alone in the USA have been estimated at 300 million dollars annually. GBS is also an important cause of maternal illness and a risk factor for preterm delivery.

Endometriosis is a benign and often progressive disease in which tissue originating in the uterine lining spreads locally by direct invasion, or through the blood vessels to distal sites. The disorder affects as many as 10–20% of women aged 30–40, although many women remain asymptomatic. Between 30% and 45% of infertile women are diagnosed with endometriosis.

In the recent past, a diagnosis of cancer was often considered a terminal condition in the majority of patients. If one did not die quickly, the stigmatism associated with the disease often relegated one to a life without children. However, as oncology treatments improved, so did the prognosis, as well as the prospect of a ‘survivor’ being able to lead a healthy productive life.

Polycystic ovary syndrome (PCOS) is among the most common endocrine disorders in females, reportedly affecting approximately 5–10% of women of reproductive age. The syndrome is characterized by oligo- or amenorrhoea, with clinical or biochemical hyperandrogenism, as evidenced by acne, hirsutism or alopecia; high serum levels of testosterone, androstenedione and dehydroepiandrosterone (DHEA) and its sulphate (DHEAS) and/or low levels of sex-hormone binding globulin (SHBG) are typical biochemical findings. Lack of internationally agreed diagnostic criteria detract from comparisons between studies reported in the literature, the diagnosis in the USA relying more on abnormal ovarian appearances using ultrasound imaging. By contrast, the diagnosis in the UK rests more heavily on clinical and biochemical features with abnormal imaging not regarded as essential for the diagnosis. Polycystic ovaries on ultrasound are defined by the presence of eight or more subcapsular cysts ≤10 mm and increased ovarian stroma. False-negative scan reports may reflect inter-operator variability while the relatively high prevalence of typical polycystic appearances in asymptomatic women adds to the uncertainties of including ultrasound imaging as a major diagnostic criterion.

Ovarian cancer is the commonest cause of death from gynaecological malignancy in the Western world. About 5000 new cases of this cancer are diagnosed each year in England and Wales (5% of all cancers), and it is the fourth commonest cancer in all women up to 85 years (after cancers of the breast, lung and large bowel). The life-time risk of developing ovarian cancer, in England and Wales, is 1 in 56, or 1.8% by the age of 85. Ovarian cancer incidence in England and Wales has increased gradually in the last two decades. Mortality rates are only slightly lower than the incidence rates – a reflection of its poor prognosis. In England and Wales, only 29% of women with the malignancy survive as long as five years after diagnosis although younger women do survive longer: 69% of those who are under 40 years old at diagnosis survive for five years compared to less than 20% for those aged 70 or more. Because of its high incidence and poor prognosis, ovarian cancer also represents the fourth most common cause of death from cancer among women in England and Wales, accounting for about 3600 deaths per year (7% of all cancer deaths).