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The incidence of 11,6% maldescent in a series of 103 cases of testicular tumours, is in accordance with the figure quoted in the literature. The malignant potential of the maldescended testis is stressed. Its relationship to age and site, and the effect of orchidopexy, are analysed. Routine orchiopexy between 5 and 7 years of age is recommended in order to prevent irreversible damage to the maldescended testis and to allow for early detection of possible malignancy.

The study of curves is an important area of research in algebraic geometry and mathematical physics. In my thesis I study so-called moduli spaces of curves; these are spaces that parametrize all curves with some specified properties. In particular, I study maps from curves to other spaces, recursive relations between numbers of curves with specified properties and equations for generating functions of these numbers. Krommen vormen een belangrijk onderzoeksgebied binnen de algebraïsche meetkunde. In mijn proefschrift bestudeer ik zogenaamde moduliruimten van krommen; dit zijn ruimten die alle krommen met gegeven eigenschappen parametriseren. Verschillende aspecten die ik onderzoek zijn afbeeldingen van krommen naar andere ruimten, recursieve relaties tussen aantallen krommen met gegeven eigenschappen en vergelijkingen voor genererende functies van dit soort aantallen.

Sacral agenesis is a heterogeneous group of congenital anomalies in which most cases are sporadic but rare familial forms also occur. Although one gene has been mapped to chromosome 7q36 in families with hemisacrum, associated with anorectal atresia and presacral mass, it is clear that the genetic aetiology of these disorders is complex and other genes remain to be discovered. Some years ago, the idea of T (Brachyury) as a candidate gene for sacral agenesis was raised, because tail abnormalities associated with T and the t complex, on mouse chromosome 17, resemble spinal defects seen in man. The recent cloning and mapping of the human T gene prompted us to re-evaluate this idea. T is a transcription factor essential for the normal development of posterior mesodermal structures. Although the sequence and function of T are highly conserved in evolution, our genetic study shows that the coding region of the human gene is highly polymorphic. Three common variable amino acid sites in known functional domains have been identified: Gly356Ser, Asn369Ser, and Gly177Asp. For the latter variant, functional studies have shown that the presence of Asp at residue 177 reduces the stability of T dimer formation. A search for rare mutation of T in 28 selected patients with sacral agenesis/anorectal atresia identified a novel, rare variant in one patient and her mother. This mutation leads to an amino acid change within a conserved activation domain. While the functional significance of this single mutation requires further investigation, we can conclude from our studies that if T has a role in the aetiology of sacral agenesis, its contribution is small in this particular set of patients. However, we cannot exclude a more major role in other forms of sacral defect. Keywords: human T gene; sacral agenesis; anorectal atresia

We have tried to review the evidence for the organisation of paediatric surgical care. Difficulties arise because of the lack of published data from district general hospitals concerning paediatric surgical conditions. Hence much of the debate about the surgical management of children is based on anecdotal evidence. However, at a time when the provision of health care is being radically reorganised to an internal market based on a system of purchasers and providers it is more important than ever to understand the issues at stake. Two separate issues have been discussed: the role of the specialist paediatric centre and the provision of non-specialist paediatric surgery in district general hospitals. There are arguments for and against large regional specialist paediatric centres. The benefits of centralisation include concentration of expertise, more appropriate consultant on call commitment, development of support services, and junior doctor training. The disadvantages include children and their families having to travel long distances for care, and the loss of expertise at a local level. If specialist paediatric emergency transport is available the benefits of centralisation far outweigh the adverse effects of having to take children to a regional paediatric intensive care centre. Specialist paediatric centres are aware of the importance of treating children and their parents as a family unit as highlighted by the Platt committee; this is an important challenge and enormous improvements have occurred to provide proper accommodation for families while their children are treated in hospital. To keep these arguments of large distances and separation from the home in context, one paediatric intensive care unit in Victoria, Australia, providing a centralised service to a region larger in are than England and with a similar admission rate, has a lower mortality rate than the decentralised paediatric intensive care provided in the Trent region of the UK. There is clear evidence that all neonatal surgery and anaesthesia should be conducted only by specialists. The debate now centres around the number of complex surgical cases a unit should treat to maintain its specialist status. The NHS executive, in its guidelines on contracting for specialist services, emphasises that "Sensible contracting needs to take into account the optimum population size not only for the stability of contracted referrals but also to give sufficient 'critical mass' for clinical effectiveness." Achieving this balance has consequences, not just for the maintenance of surgical expertise, but for the essential ancilliary services. There is clear evidence in anaesthesia that anaesthetists doing small numbers of neonatal procedures had significantly worse results. The same seems to be true in the fields of oncology, radiology, pathology, and intensive care. The reasons why the results of management of certain paediatric conditions are better at specialist centres are open to speculation. Presumably greater exposure to rare complex cases, concentration of expertise, more peer review, and a trickle down effect of the multidisciplinary approach all help to keep health care workers up to date with current world practice. In addition, it allows for appropriate specialist on call rotas and dedicated junior staff. If insufficient numbers of specialist surgical cases are being treated at a centre then the whole multidisciplinary team suffers. The 1989 NCEPOD report states "that paediatricians and general surgeons must recognise that small babies differ from other patients not only in size, and that they pose quite separate problems of pathology and management." The need for large centres of paediatric surgical expertise is now accepted by the Royal College of Surgeons of England, the British Association of Paediatric Surgeons, the Senate of Surgery of Great Britain and Ireland, the Royal College of Paediatrics and Child Health, the Royal College of Anaesthetists, the Audit