Infant leukaemias and cot deaths

Medullary serotonin defects and respiratory dysfunction in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is defined as the sudden and unexpected death of an infant less than 12 months of age that occurs during sleep and remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. It is the leading cause of postneonatal mortality in the developed world. The cause of SIDS is unknown, but is postulated to involve impairment of brainstem-mediated homeostatic control. Extensive evidence from animal studies indicates that serotonin (5-HT) neurons in the medulla oblongata play a role in the regulation of multiple aspects of respiratory and autonomic function. A subset of SIDS infants have several abnormalities in medullary markers of 5-HT function and genetic polymorphisms impacting the 5-HT system, informing the hypothesis that SIDS results from a defect in 5-HT brainstem-mediated control of respiratory (and autonomic) regulation. Here we review the evidence from postmortem human studies and animal studies to support this hypothesis and discuss how the pathogenesis of SIDS is likely to originate in utero during fetal development.

Season of birth and diagnosis of children with leukaemia: an analysis of over 15 000 UK cases occurring from 1953-95

If infections are involved in the aetiology of childhood leukaemia then seasonal variation in the birth or onset dates of the malignancy may be apparent. Previous studies that have examined seasonality of these dates have produced conflicting results. Using population-based data from the National Registry of Childhood Tumours we conducted a larger study than any to date of 15 835 cases of childhood leukaemia born and diagnosed in the UK between 1953-95. We found no evidence of seasonality in either month of birth or month of diagnosis overall or in any subgroups by age, sex, histology or immunophenotype. We did however find a significant (P = 0.01) February peak in month of birth for cases born before 1960 and a significant (P = 0.02) August peak in month of diagnosis for those diagnosed before 1962. Whilst these findings may be due to chance they are also consistent with changes over time in the seasonality of exposure, or immunological response, to a relevant infection. Changes in the seasonal variation in the fatality rate of a pre-leukaemic illness, such as pneumonia, could be another explanation.

Childhood cancers and competing causes of death

From the survey that first identified cancer effects of foetal irradiation and related sources has come support for the following hypotheses: (1) competing causes of death for childhood cancers include abortions (solid tumours) and infections (RES neoplasms); (2) the forms taken by RES neoplasms vary with the nature and intensity of indigenous infections; (3) ideal conditions for developing diffuse RES neoplasms (leukaemia) include the gross immunological incompetence caused by trisomy 21; (4) the unusually localised RES neoplasms found in children who have survived repeated attacks of malaria (Burkitt lymphoma and chloroma) are probably the result of these children having exceptionally high levels of passive as well as active immunity; and (5) when teratogenic effects of in utero mutations include faulty erythropoiesis as well as faulty leucopoiesis, infections are not the only rival causes of death.

Effect of ambient temperature on SIDS rate

OBJECTIVE

To examine the relationship between ambient temperature and rate of sudden infant death syndrome (SIDS).

SUBJECTS AND SETTING

All infants with SIDS occurring during 1980-1989 in the Sydney metropolitan area.

RESULTS

The SIDS rate varied more than threefold over the months of the year and peaked at the minimum daily temperature in July. The rate was negatively linearly related to both the monthly mean minimum and maximum daily temperatures. Both relationships were highly significant (P < 0.001).

CONCLUSION

The significant relationship between daily temperature and SIDS rate means either that daily temperature is an excellent indicator of the cold weather conditions that have a profound effect on the rate of SIDS or that temperature itself plays a direct role in the cause of SIDS.

Etiology of childhood leukemia: a possible alternative to the Greaves hypothesis

Whenever a country has experienced a significant decrease in infant mortality there has always been a concomitant increase in childhood cases of acute lymphoblastic leukemia (ALL). According to Greaves, this increase is the result of a new type of leukemia, which was first seen in Britain between 1920 and 1940. An alternative hypothesis is proposed which assumes that, for childhood cases of ALL, infections are competing causes of death and for juvenile myeloid leukemia (JML) the principal competitor is the sudden infant death syndrome (SIDS). The SIDS association is the result of JML originating in undifferentiated (erythro-myeloid) stem cells and having faulty erythropoiesis as a side effect. With this congenital anomaly as part of the disease process, the low oxygen pressures of deep sleep may be sufficient to cause sudden death from tissue anoxia.

Cystic fibrosis complicated by acute leukemia

During a 3-month period, two men ages 20 and 25 years, respectively, with cystic fibrosis developed acute lymphocytic and nonlymphocytic leukemias, respectively. These two patients were among 120 patients who attended our cystic fibrosis clinic during the last 3 years. Thirty-five of the 120 patients have survived beyond the second decade. The authors ask whether acute leukemia will be recognized with increasing frequency in cystic fibrosis patients who achieve prolonged survival.

The immune system and cancers of foetal origin

Evidence of early loss of immunological competence in cases of neoplasms occurring in juveniles was found in an analysis of OSCC data (Oxford Survey of Childhood Cancers). The effects observed included heightened sensitivity to infection from birth onwards for all types of childhood cancer, higher levels of sensitivity for leukaemia than for lymphomas, and higher levels for lymphomas than for other solid tumours. The findings as a whole are consistent with in utero loss of immunological competence, which is an essential promoter of cancers of foetal origin and thus allows the outcome of an in utero cancer induction to be influenced both by maternal levels of immunological competence and postnatal infection.