The delay in childbearing is an important societal change contributing to an increasing incidence of subfertility. The prevailing concept of female reproductive ageing assumes that the decline of both quantity and quality of the oocyte/follicle pool determines an age-dependent loss of female fertility. There is an apparent discrepancy between the ability to maintain a regular ovulatory cycle pattern and the several years earlier cessation of female fertility. This latter is largely explained by an age-related increase of meiotic non-disjunction leading to chromosomal aneuploidy and early pregnancy loss, such that most embryos from women > or =40 years old are chromosomally abnormal and rarely develop further. The final stage of reproductive ageing-the occurrence of menopause-shows a huge variation between women. Age at last birth in natural fertility populations, which marks the end of female fertility, shows an identically wide variation as age at menopause, but occurs on average 10 years earlier. Given the high heritability for age at menopause, the variation in both age of menopause and last birth are probably under genetic control by the same set of genes. Some of those genes must carry heritable variants which modulate the rate of ovarian ageing and give rise to the wide age variations for the various phases of reproductive ageing.

Domesticated animal species such as dogs and cats, with their many different characteristics and breed-specific diseases, and their close relationship and shared environment with humans, are a potentially rich source for the identification of the genetic contribution to human biology and disease. Copper toxicosis in Bedlington terriers is a genetic disease occurring with a high prevalence worldwide and is unique to this breed. Copper homeostasis appears to be well regulated in mammals. Two copper carrier proteins have been identified in man and rodents which, when dysfunctional, cause either copper deficiency (Menkes disease) or copper accumulation in various tissues (Wilson disease). However, these proteins are not primarily involved in the biliary excretion of copper. Bedlington terriers have a high prevalence of copper toxicosis and it is well documented that their biliary excretion of copper is impaired. This disease is of direct relevance for the understanding of copper metabolism in mammals. Previously, we mapped the copper toxicosis gene to dog chromosome region 10q26. Based on DNA samples obtained from privately owned dogs, we were able to confine the localization of the copper toxicosis gene to a region of <500 kb by linkage disequilibrium mapping. While screening genes and expressed sequence tags in this region for mutations we found that exon 2 of the MURR1 gene is deleted in both alleles of all affected Bedlington terriers and in single alleles in obligate carriers. Although the function of the MURR1 gene is still unknown, the discovery of a mutated MURR1 gene in Bedlington terriers with copper toxicosis provides a new lead to disentangling the complexities of copper metabolism in mammals.

Adult polycystic kidney disease (APCKD) is a common and often lethal multi-organ disease with an autosomal dominant pattern of inheritance; approximately 1 in 1,000 people carry the mutant gene. The major pathological abnormality is the development and progressive enlargement of cysts in several organs including the liver, pancreas and spleen as well as the kidneys. The basic biochemical defect which leads to the formation of cysts remains unknown. Cyst development, which is not retarded by any known therapy, leads to irreversible renal failure and death at a mean age of 51 unless dialysis or transplantation are used. Patients with the disease account for 9% of chronic dialysis requirement. The first symptoms tend to occur in the fourth decade, after most patients have reproduced. Presymptomatic diagnosis depends on the ultrasonographic detection of cysts, but exclusion cannot be achieved by this means; 34% of at-risk patients in the second decade and 14% in the third will go on to develop cysts after negative diagnosis. The low sensitivity of diagnostic techniques in this critical age-range imposes severe limitations on genetic counselling and the condition cannot be identified prenatally. Hence we have searched for a linkage marker for APCKD; we show here that the APCKD locus is closely linked to the alpha-globin locus on the short arm of chromosome 16 (zeta = 25.85, theta = 0.05).

A genome scan was performed on 164 Dutch affected sib pairs (ASPs) with attention-deficit/hyperactivity disorder (ADHD). All subjects were white and of Dutch descent and were phenotyped according to criteria set out in the Diagnostic and Statistical Manual Of Mental Disorders, 4th edition. Initially, a narrow phenotype was defined, in which all the sib pairs met the full ADHD criteria (117 ASPs). In a broad phenotype, additional sib pairs were included, in which one child had an autistic-spectrum disorder but also met the full ADHD criteria (164 ASPs). A set of 402 polymorphic microsatellite markers with an average intermarker distance of 10 cM was genotyped and analyzed using the Mapmaker/sibs program. Regions with multipoint maximum likelihood scores (MLSs) >1.5 in both phenotypes were fine mapped with additional markers. This genome scan indicated several regions of interest, two of which showed suggestive evidence for linkage. The most promising chromosome region was located at 15q, with an MLS of 3.54 under the broad phenotype definition. This region was previously implicated in reading disability and autism. In addition, MLSs of 3.04 and 2.05 were found for chromosome regions 7p and 9q in the narrow phenotype. Except for a region on chromosome 5, no overlap was found with regions mentioned in the only other independent genome scan in ADHD reported to date.