Population-based risk estimates of Wilms tumor in sporadic aniridia. A comprehensive mutation screening procedure of PAX6 identifies 80% of mutations in aniridia.

Aniridia is a severe eye disease characterized by iris hypoplasia; both sporadic cases and familial cases with an autosomal dominant inheritance exist. Mutations in the PAX6 gene have been shown to be the genetic cause of the disease. Some of the sporadic cases are caused by large chromosomal deletions, some of which also include the Wilms tumor gene (WAGR syndrome), resulting in an increased risk of developing Wilms tumor. Based on the unique registration of both cancer and aniridia cases in Denmark, we have made the most accurate risk estimate to date for Wilms tumor in sporadic aniridia. We have found that patients with sporadic aniridia have a relative risk of 67 (confidence interval: 8.1-241) of developing Wilms tumor. Among patients investigated for mutations, Wilms tumor developed in only two patients out of 5 with the Wilms tumor gene (WT1) deleted. None of the patients with smaller chromosomal deletions or intragenic mutations were found to develop Wilms tumor. Our observations suggest a smaller risk for Wilms tumor than previous estimates, and that tumor development requires deletion of WT1. We report a strategy for the mutational analysis of aniridia cases resulting in the detection of mutations in 68% of sporadic cases and 89% of familial cases. We also report four novel mutations in PAX6, and furthermore, we have discovered a new alternatively spliced form of PAX6.

Methodological problems in assessing health-related, neuropsychological effects of lead absorption in a very low-level exposed area.

Methodological problems in the low level lead studies are reviewed using the Aarhus lead study as an example. It is shown that a lead effect can be found in an area where the background blood lead level is as low as 37 micrograms/l (geometric mean). Even in such an area it is worthwhile looking for populations at risk. It is shown that attrition causes confounding with a directional bias towards the null-hypothesis. Longitudinal studies are associated with this type of bias. Misclassification as for past exposures will also have a bias of this type. Studies depending on blood-lead measures are liable to have this type of bias. This is the case to a lesser degree in studies using cumulated indices. Subsamples of tooth dentin (circumpulpal dentin) satisfies the requirement for an index for cumulated lead absorption. Since lead absorption requires motor abilities, medical factors that are risk factors for motor development as well as for the other developmental outcome are also confined with a directional bias towards the null-hypothesis. It is suggested to exclude for such factors. Lead seems to be a ubiquitous noxious substance. Any community should have a strategy to minimize its effects.

Tetrasomy 18p de novo: parental origin and different mechanisms of formation.

We have used eight PCR-based DNA polymorphisms to determine the parental origin and mechanisms of formation in 9 patients with de novo nonmosaic tetrasomy 18p. The 9 patients, 4 girls and 5 boys, had clinical features characteristic of i(18p) syndrome. The supernumerary marker chromosome was identified by fluorescence in situ hybridization (FISH) analysis using centromeric probes and a flow-sorted 18p-specific library. The isochromosome was of maternal origin in all 9 cases. The formation of tetrasomy 18p cannot be explained by a single model. In 6 cases, meiosis II nondisjunction, followed by subsequent postzygotic misdivsion, and in 1 case postzygotic nondisjunction and postzygotic misdivision were the most likely mechanisms of formation. Alternative mechanisms are suggested in the remaining 2 cases.

[Subcutaneous fat necrosis with hypercalcemia]. / Subkutan fedtnekrose med hyperkalcaemi.

A case of subcutaneous fat necrosis (SFN) is presented. The infant developed late onset hypercalcaemia of severe degree. Calcitonin failed to normalize the hypercalcaemia. Glucocorticoids and withdrawal of dietary calcium and vitamin D are the treatment of choice. Like hypercalcaemia in association with other granulomatous diseases, SFN is possibly secondary to locally produced 1,25-dihydroxy-cholecalciferol. Our results were not able to confirm this theory. Infants with SFN should have calcium levels monitored closely for months.

Value of chromosome painting in determining the chromosomal outcome in offspring of a 12;16 translocation carrier.

We currently use direct and reverse chromosome painting in prenatal diagnosis. In a family with a subtle 12;16 translocation, adjacent 1 segregation was diagnosed in the first child, a boy, in whom symptoms compatible with partial trisomy 16p and partial monosomy 12q were seen. In the next pregnancy, a chorionic villus biopsy was tested using chromosome painting. Only by supplementing conventional cytogenetic methods with molecular cytogenetic techniques could the true karyotype be unequivocally determined. Reverse painting, using DOP-PCR amplified, flow sorted paternal derivative chromosomes as a DNA library to paint the chorionic villus cells, was especially informative.

Early lead exposure and neonatal jaundice: relation to neurobehavioral performance at 15 years of age.

A cohort of children who attended first grade in 1983 was identified in a Danish community with low-level lead pollution. Two groups with high and low postnatal lead exposure were generated on the basis of the dentin-lead concentration in shed deciduous incisors. At age 8 years, examination of 162 children matched according to gender and socioeconomic status had shown lead-related deficits in verbal intelligence and visuomotor coordination. Re-examination was now carried out in 141 children at age 15 years using the Wechsler Intelligence Scale for Children (WISC), Bender Visual Motor Gestalt, Trail Making, and Visual Gestalts. In general, no lead-related effects could be detected in the group. However, in children with a history of neonatal jaundice, increased lead exposure was associated with mild neurobehavioral deficits, as indicated by lower verbal IQ scores and decreased visuomotor coordination. This finding suggested that moderate neonatal hyperbilirubinemia may have precipitated an increased sensitivity to subsequent exposure to lead.

Lessons from a Danish study on neuropsychological impairment related to lead exposure.

Serious problems emerge when evaluating evidence on lead neurotoxicity in children. The extent of these problems and ways to control them were explored in a study of 1291 children from the first class in the schools of Aarhus municipality, Denmark. The lead retention in circumpulpal dentin in shed deciduous teeth was used as an indicator of cumulated lead exposure; it correlated most strongly with traffic density at the residence of each family and at the day-care institutions. In a nested case-control group selected on the basis of dentin lead concentrations, 29 of 200 children had encountered obstetrical complications and other medical risks for neurobehavioral dysfunction; these children primarily belonged to the low-lead group. As lead-related neurobehavioral effects are nonspecific, inclusion of these children in the data analysis would therefore have distorted the results toward the null hypothesis. Children from the high-lead group who had experienced neonatal jaundice showed impaired performance when compared to other high-lead children; this finding may suggest a synergistic effect. The Bender gestalt test scored by the Göttingen system was the test that was most sensitive to lead exposure. The conclusion that neurobehavioral effects can be caused by the relatively low lead exposures in Denmark may not be surprising, as current exposures to this toxic metal greatly exceed the prepollution levels to which the human body originally adapted.

Lead concentration in deciduous teeth from Danish school children.

Deciduous teeth were collected from school children in the first grade in six Danish municipalities; 2,033 teeth were received from 1,848 children. The geometric mean for the largest group (from Arhus) was 8.4 micrograms/g. The lead concentrations were similar in two Copenhagen suburbs with a secondary lead and a lead battery factory (geometric means, 9.6 and 9.9 micrograms/g, respectively). Increased lead concentrations were seen in children of low social class, in those whose fathers were automechanics or shipyard workers. Another part of the study showed that children residing in areas with heavy traffic also were at risk for increased lead retention. Thus, automobile exhausts and indirect occupational exposure appear to be important sources of lead retention in children, while a contribution from industrial emissions could not be detected.

Validity and interpretation of blood lead levels: a study of Danish school children.

Blood lead concentrations were measured in a group of children from a group of 9- to 10-year-old school children in Aarhus, Denmark. The study group was selected as a high-level and a low-level lead group, as identified by the lead concentration in the circumpulpal dentine in deciduous teeth shed 2-3 years previously. The validity of the blood sampling technique was investigated in adult volunteers, and lead was determined by electrothermal atomic absorption. Capillary blood sampling by a finger-stick method was preferred, as the slight contamination caused by this technique was deemed acceptable. The children with the highest dentine lead levels (n = 70), had blood lead concentrations of 0.08-0.63 mumol/l and a geometric mean of 0.28 mumol/l. The children with lowest dentine levels (n = 76) had blood lead concentrations of 0.08-0.70 mumol/l and a geometric mean of 0.18 mumol/l. The blood lead concentrations were compared with interview data on behaviour, family habits, diet, parents' tobacco smoking and occupation, water lead measurements, and traffic counts. A total of 20% of the variation in blood lead was explained by parents' tobacco smoking, the child's number in the sibship, gender, and consumption of canned food at home.

Learning disabilities in children: significance of low-level lead-exposure and confounding factors.

The hypothesis that low-level lead absorption is a risk factor for learning disabilities in school children was examined in the municipality of Aarhus, Denmark. During 1982-1983, a total of 1,302 children in the first grade (54% of the eligible population) delivered shed deciduous teeth. The lead concentration in the circumpulpal dentin was used as an indicator of the cumulated lead absorption, and 200 cases (high-lead) and controls (low-lead) were selected, and matched for socioeconomic group and gender. The parents were interviewed regarding the child's development and past medical history. Possible confounders were identified and controlled for in a logistic multivariate model. The influence of lead absorption became statistically significant only after exclusion of the children with proven medical risk factors, thereby the adjusted odds ratio in the weighted analysis was changed from 2.2 to 4.3. Thus, in a Scandinavian low-level lead-polluted area, lead absorption appears to be a risk factor for learning disabilities.

Predictors of tooth-lead level with special reference to traffic. A study of lead-exposure in children.

Possible predictors of the lead burden of children were investigated in a low-exposure area. A total of 1302 school children in the first form within the municipality of Aarhus, Denmark, donated deciduous teeth for determination of the lead concentration in the circumpulpal dentin. The families were interviewed on possible sources of lead. Present and former addresses of residences and day-care institutions were obtained, and the traffic intensity was estimated at each of these addresses. Children with a high lead burden resided significantly more often in heavily-travelled streets than children with a low burden, but only during their first 3 years of life. The increased risk for a high lead burden was related to the traffic intensity in a dose-response manner. Further, children with a high lead burden more often exhibited pica, their mothers smoked more during pregnancy, and their fathers were more likely to work at a garage or shipyard. In a logistic multivariate regression, such parental occupation increased the risk for a high lead burden 1.5-fold (ORadj; P = 0.03), whereas tobacco and traffic each were of borderline significance (ORadj = 1.4, P = 0.08).

A neuropsychological study of children with elevated dentine lead level: assessment of the effect of lead in different socio-economic groups.

The study was carried out in the municipality of Aarhus, a city of 250,000 inhabitants. The study was designed as a cross-sectional cohort study of school children in first grade in 1982-83. A total of 2,412 children were contacted and asked to submit their shed teeth to the teacher, and 1,291 children delivered at least one usable tooth (response rate, 54 percent). The lead level in circumpulpal dentin showed an average of 10.7 micrograms/g. Eight percent of the children (N = 110) had a lead level above 18.7 micrograms/g and were selected as a "high" lead exposure group. This group was matched by sex and socio-economic status of the parents with control children with a dentin lead level below 5 micrograms/g. Following a detailed interview with the parents, children were excluded from the study if medical risk factors were present. A clinical psychologist, blind to the lead data, administered selected psychometric tests to 162 of the children selected. The high-lead children scored lower on the WISC when compared to low-lead children, especially on the Verbal IQ (p less than 0.001) and Full Scale IQ (p less than 0.01). No significant difference was seen between the high- and low-exposure groups on the Performance IQ and on several experimental tests. Impaired function associated with lead exposure was also found on the Bender Visual Motor Gestalt Test (p less than 0.001) and on a behavioral rating scale (p less than 0.01). These results remained statistically significant even after controlling for socio-economic status and other confounding variables.

Neurological deficits in children: medical risk factors and lead exposure.

A study of possible undue neurobehavioral effects of low-level lead exposure was performed in Danish school children who entered first grade in 1982. Lead absorption was found to relate to impaired psychological test performance and difficulties at school. However, this relationship was confounded by medical risk factors for neurological deficit. Such factors were used as exclusionary criteria before psychological testing and were selected a prior on the basis of a critical evaluation of known etiologies of neurobehavioral dysfunction. Children characterized by a medical risk factor tended to show performance below average and, at the same time, low lead absorption. The medical risks were also associated with delayed motor activity in the first year of life, thus perhaps resulting in diminished lead intake. This confounding effect makes strict exclusion for proven medical risk factors crucial to avoid bias toward the null-hypothesis. In spite of strict exclusion, a residual confounding due to health-related variables still remained. Inconsistent findings in the field of neurobehavioral studies may be partly explained by different means of identification and statistical treatment of medical risk factors.

Traffic a source of lead exposure in childhood.

Experimental and observational data has long implicated automobile exhaust from leaded petrol as a major source of human lead exposure. The present study evaluates the association of individual traffic exposure with individual lead absorption. A case-referent study was carried out on 1302 out of 2412 children in the municipality of Aarhus - Denmark. Shed deciduous teeth were matched for sex and socioeconomic status. Individual lead sources were assessed by an interview. Information on former addresses and the data of address change was obtained as was information on the daily number of cars driving on all roads of the city. A traffic index was constructed describing the traffic density at the home. An association between high lead and high traffic density was found in the children at the age of 6 months to 2 years. This relationship was of a dose-response nature. The association was not account for by other possible major sources.

Bias from non-participation: a study of low-level lead exposure in children.

Epidemiological studies on neurobehavioural effects in childhood are highly sensitive to selection bias. A study on the significance of low-level lead exposure was performed among school children in the first grade in Aarhus in 1982-83. Deciduous teeth were collected and analysed for the circumpulpal dentin lead concentration. On the basis of the lead levels, a case and a control group were identified. Information on socioeconomical status and past medical history was obtained for all children. A "common sense" stratification of the reason for non-participation, showed bias in particular due to non-responders, while "refusers" caused little, if any bias. A non-participation of 7% significantly distorted the main result of the study in the direction of the null-hypothesis. Current studies of low-level lead exposure vary greatly with regard to non-participation and the extent of selection bias may contribute to understand the apparent diversity of findings of studies in this field.

Lead concentration in deciduous teeth: variation related to tooth type and analytical technique.

A total of 245 newly shed deciduous incisors were obtained from 114 first-grade children who each contributed more than one tooth. Lead concentrations averaged about fivefold higher in circumpulpal dentin than in the whole tooth, but the two parameters showed little correlation. A considerable intraindividual variation in lead levels was partly related to tooth type. In particular, whole upper central incisors contained more lead than did other incisors, but the reverse applied to circumpulpal dentin lead concentration. As whole-tooth and circumpulpal lead concentrations may represent different compartments, tooth lead analyses must be interpreted accordingly. Lead levels in circumpulpal dentin would appear to be a meaningful indicator of long-term lead retention in population studies of children.