Changing concepts concerning the pathogenesis of infectious diseases

Parental age and seasonal variation in the births of children with sporadic retinoblastoma: a mutation-epidemiologic study

Statistical analysis of parental age data from 225 sporadic cases of bilateral retinoblastoma, plus ten sporadic cases of chromosome deletion or translocation involving 13q14 that was identified as of paternal origin, revealed no evidence of paternal or maternal age effect. Parental exposure to ionizing radiation or chemical mutagens, the effect of which is accumulated with advancing age, does not seem to play a major role in the production of germinal mutations at the responsible (RB) locus. Furthermore, analysis of variation in the month of birth of 753 children with sporadic unilateral retinoblastoma did not show any significant deviation from the controls or a cyclic trend. The occurrence of nonheritable retinoblastoma is not likely to be associated with certain viruses such as human adenovirus 12 whose activity varies markedly with season. These results, together with the fairly uniform pattern in the incidence of this tumor among different populations, suggest that most, if not all, cases of sporadic retinoblastoma are caused by some intrinsic biological mechanisms, and not by environmental mutagens that may vary with respect to time and place.

Cytogenesis in the developing retina of the cat

Cytogenesis in the cat retina was studied using tritiated (3H) thymidine autoradiography and nuclear stains. Three zones of cell division were recognized. In the first zone cell cleavage occurs at the outer limiting membrane. The distribution of these mitotic figures is uniform as early as an embryonic age of 29 days (E29) until E50. At about E50 a "cold spot", made apparent by the absence of mitotic figures, is evident at the site of the developing area centralis. This spreads to encompass the whole retina by postnatal day 10 (P10). A second zone of cell division was recognized by the presence in the developing inner nuclear layer of 3H-thymidine labelled nuclei which do not migrate to the outer limiting membrane (ventricular surface) to divide. Some of these labelled nuclei are located in regions of the retina where cytogenesis at the ventricular surface has ceased. A third zone was observed in the optic nerve fibre/ganglion cell layers from about E54 until beyond the first postnatal month. This activity gives rise to vascular endothelial cells in the nerve fibre/ganglion cell layers. Once established, the developing vascular cells invade the inner plexiform and inner nuclear layers to form the deeper capillary net.

Immunocytochemistry of neuronal and glial markers in retinoblastoma

An immunocytochemical study of 30 retinoblastomas was carried out using antibodies to neuronal and glial markers. The tumours were found to react with antibodies to neuron-specific enolase (NSE), a marker for neuronal elements, and S-100 and glial fibrillary acidic protein (GFAP), both of which are proteins present in glia. Two distinct cell populations were found within the tumour: the first, composed of anaplastic tumour cells at various stages of differentiation, showed both NSE and S-100 immunoreactivity; the second cell type, which immuno-stained for S-100 and GFAP, resembled mature glial cells. The results of this study indicate that the retinoblastoma may arise from a pluripotential primitive cell partially retaining neuronal and glial characteristics.

The incidence and epidemiology of retinoblastoma in New Zealand: A 30-year survey

One hundred cases of retinoblastoma were diagnosed in New Zealand-born children between 1948 and 1977 inclusive. Five patients had an affected parent, and of the remaining sporadic cases 25 had bilateral and 70 unilateral tumours. The frequency of retinoblastoma, 1 in 17,500 births, was similar to that reported for most other countries. There was no evidence of an increase in the incidence of all cases of sporadic retinoblastoma during the 30-year period studied, nor was there any significant fluctuation in their incidence with space and time. There was an excess of bilateral sporadic cases in the southern-most districts of New Zealand, but this was of marginal significance. There was no significance evidence for any environmental influence on the occurrence of retinoblastoma.

Bilateral retinoblastoma with ectopic intracranial retinoblastoma: trilateral retinoblastoma

In 11 patients, bilateral retinoblastoma presented at a mean age of 6 months and pineoblastoma at 4 years. We suggest that the hereditary multicentric retinoblastoma arose in vestigeal photoreceptors in the pineal as well as in the hypothetical retinoblasts of the retina. In certain lower animals, the pineal functions as a photoreceptor organ, resembles the retina histologically, and is described as a "third eye." Hence, the patients we describe may be considered as having "trilateral retinoblastoma." Two possible variants of this entity were also noted: (1) three children without retinoblastoma with rosettes and photoreceptor differentiation characteristic of retinoblastoma, and (2) three additional cases involving children who presented with retinoblastoma-like tumors in the suprasellar or parasellar region 2 to 6 months before the discovery of intraocular retinoblastoma. These observations suggest that the retinoblastoma gene confers a previously unappreciated susceptibility to a narrow spectrum of neuroblastic tumors, which usually present in the retina but which can also occur ectopically.

The role of viruses in the development of ocular tumors

The role of viruses as a cause of human cancer has been investigated by a variety of techniques in recent years. While no definitive answer exists at present, several lines of evidence indicating a viral role in human tumors and reviewed. These include the well-documented role of viruses in causing animal tumors; evidence for an association of certain viruses with human tumors; and virally induced animal models of human tumors, melanoma, retinoblastoma, and ocular malignant melanoma.

Slow virus infections

Slow viruses produce diseases whose incubation periods range from several months to many years. Because of this long latency period, the lack of inflammation produced by these diseases and the lack of recoverable virus particles, it is only recently that the association has been made between the viruses and the diseases they cause. The detailed study of kuru, a neurologic affliction of a remote tribe of cannibals in New Guinea, was responsible for the synthesis of new and previously gathered information into a unified framework to explain not only kuru but other diseases as well. Since then, animal models, transmission experiments and histologic and biochemical studies have unveiled new links connecting viruses to previously obscure neurologic, neurophthalmic and ophthalmic entities.