[Santiago Ramon y Cajal and neurobiology]. / "Idéer - liksom den vita näckrosen - blommar endast i stilla vatten" (Don Santiago Ramón y Cajal).

In 2001 the centennial of the first Nobel Prizes is celebrated. This essay, which portrays the Nobel Laureate in Physiology or Medicine in 1906 Don Santiago Ramón y Cajal, should be seen as a contribution to that celebration. The aim of the essay is to present one of the founders of modern neuroscience and greatest scientists of all time, his life history, personality, working methods and driving forces as well as his scientific contributions. The title of the essay "Ideas -- like the white water-lily - flourish only in tranquil waters" is a quotation from Ramón y Cajal which characterizes him very well as a scientist. He was extremely productive, he made fundamental contributions to a number of fields within neurobiology with a very few mistakes, and he did it all by himself.

Maternal smoking and irradiation during pregnancy as risk factors for child leukemia.

The effect of joint exposure to diagnostic X-rays and maternal smoking during pregnancy was compared in a case-control study of 216 children with cancer (128 cases with acute lymphoblastic leukemia [ALL] and 88 with solid tumors) and 301 control children with insulin-dependent diabetes mellitus (IDDM). Exposure to diagnostic X-rays combined with smoking of ten or more cigarettes per day gave a relative risk of 3.6 (95% CI, 1.8 to 7.0) and a positive dose response relation for ALL in the offspring (p less than 0.001). When examined alone, X-rays gave a relative risk of 1.8 (95% CI, 1.1 to 3.1), and smoking a relative risk of 2.2 (95% CI, 1.1 to 4.5). No similar trend was seen for solid tumors. Potential confounding was examined after stratification on maternal smoking-diagnostic X-ray exposure and each of potential confounders, but there was little change in the risk ratio. We conclude that the risk of ALL in the offspring was more than threefold higher when smoking was combined with diagnostic X-ray during pregnancy.

No evidence of mutations in four candidate genes for male sex determination/differentiation in sex-reversed XY females with campomelic dysplasia.

Campomelic dysplasia (Cd) occurs combined with sex reversal resulting in XY females. The recent identification of candidate genes for sex determination/differentiation and of a sex determining region on the human Y chromosome prompted the authors to study these genes for mutations in patients with Cd and sex reversal. In a total of five cases, no evidence for a mutation in the genes SRY, ZFY, ZFX, MEA and some anonymous Y-linked sequences was found. In addition to Southern analysis, gene expression of ZFY, ZFX and MEA was found to be normal as well. It is concluded that sex reversal in this condition is due to mutation in a so far unidentified gene which may act secondary to the testis-determining factor (TDF).

Haplotyping of the human porphobilinogen deaminase gene in acute intermittent porphyria by polymerase chain reaction.

Acute intermittent porphyria (AIP) is due to a defect in porphobilinogen deaminase (PBGD, E.C. 4.1.3.8) inherited as an autosomal dominant trait. Presymptomatic carrier detection is important in order to avoid exposure to factors inducing severe clinical symptoms. Carriers and noncarriers of the AIP gene can be distinguished by linkage analysis using three intragenic RFLPs in AIP families. In the present study, the polymerase chain reaction (PCR) was used to amplify 3.3-kb genomic sequences covering three polymorphic sites. Haplotypes were identified after cleavage of amplified products with three restriction enzymes, showing that the technique can be successfully used for linkage analysis in AIP families.

The distribution of the gene for the juvenile type of Gaucher disease in Sweden.

A study of 30 Swedish families with the Norrbottnian type of Gaucher disease provides evidence for two clusters of the gene, one close to Overkalix in the northern part of the county of Norrbotten and the other in the vicinity of Arvidsjaur in the southern part of the same county. The gene for Gaucher disease in Overkalix appeared later than that in Arvidsjaur. A founder moving from Arvidsjaur to Overkalix during the seventeenth century or two different mutations are the most likely explanations of this finding.

DNA polymorphisms within the porphobilinogen deaminase gene in two Swedish families with acute intermittent porphyria.

Two unrelated families with acute intermittent porphyria (AIP), an autosomal dominant disease related to a defect in porphobilinogen deaminase (PBG-D, EC 4.1.3.8.), were studied with regard to three restriction fragment length polymorphisms (RFLPs) (MspI, PstI, BstNI) within the PBG-D gene. The results indicate that linkage analysis of RFLPs within the gene can be used as a complement to PBG-D analysis for the diagnosis of gene carriers in families with AIP.

A linkage study of the locus for X-linked Charcot-Marie-Tooth disease.

A large family with Charcot-Marie-Tooth disease, showing a probable X-linked incomplete dominant inheritance, was studied by linkage analysis. Results, obtained by the use of X chromosome specific DNA probes of known regional location, suggest that the disease locus is linked to the DXYS1 locus (z = 2.59 at theta = 0.00) and to the DXS14 locus and, places the disease locus between the DXYS1 locus and the DXS14 locus, near the centromere of the X chromosome. Together with the published data, a distance of 13 cM (z = 6.95) was assessed between the disease locus and the DXYS1 locus.

Segregation analysis of balanced pericentric inversions in pedigree data.

The results of the recent European collaborative prenatal study suggested a segregation distortion of balanced pericentric inversions from carrier fathers but not carrier mothers (Boué & Gallano 1984). In an attempt to confirm these unexpected results, we examined 216 pedigrees with balanced pericentric inversions collected from three centers and from the literature. We were unable to detect any significant deviation from the expected 1:1 segregation of balanced pericentric inversions to normal karyotypes among the offspring of either carrier parent. To clarify the discrepancy between the studies, we reanalyzed the data from the prenatal study using all karyotyped individuals and, assuming conventional ascertainment rules, found a normal segregation pattern. We conclude that balanced pericentric inversions segregate normally in both males and females and that some retrospectively selected pedigrees were included as prospective in the prenatal study and this misclassification caused the apparent segregation distortion from carrier fathers.

Maternal smoking during pregnancy and risk of childhood cancer.

In a case-control study of childhood cancer a dose-response relationship was found between the number of cigarettes smoked per day by the mother during pregnancy and cancer risk in the offspring. When all tumour sites were considered the cancer risk was 50% higher for the most exposed group than for the controls. The risk was doubled for non-Hodgkin lymphoma, acute lymphoblastic leukaemia, and Wilms' tumour. These findings provide further evidence for the harmful effects of cigarette smoke on the growing fetus.

Changes in the incidence of Down syndrome in Sweden during 1968-1982.

A continuous increase in the incidence of Down syndrome in Sweden was noted during 1979-1981. This increase mainly occurred among children of younger mothers and was more pronounced for the males than for the females. There was no evidence of a significant seasonal variation, increased frequency of prematurely born children, or decrease in the number of cases aborted after prenatal diagnosis. An analysis of the whole 15-year period indicates that the incidence of Down syndrome has increased slowly in both sexes, and that there might have been a superimposed cyclic variation limited to the males.

A family study of genetic and environmental factors determining polymorphic hydroxylation of debrisoquin.

Debrisoquin hydroxylation capacity determined as the ratio of debrisoquin to 4-OH-debrisoquin (DMR) in urine after a single oral dose (10 mg) was studied in 52 nuclear families comprising 226 subjects. The relative importance of genetic and environmental factors for DMR was studied by path analysis. There was a significant negative correlation between DMR and coffee intake but no significant correlations between DMR and sex, age, alcohol intake, or smoking habits. Path analysis showed that genetic heritability was 0.79 while cultural heritability was only 0.06. Complex segregation analysis gave evidence for a major locus with incomplete dominance (d = 0.28) between a recessive and an additive gene. The frequency of the major gene was 0.31, allowing an estimate of the frequency of slow hydroxylators in the Swedish population of 9.4%. There was also evidence for a multifactorial component accounting for 14% of the total variation. It was not possible to distinguish between the different genotypes within the rapid hydroxylator phenotype. Our data agree with previous studies in British and German populations showing that two alleles at a major autosomal locus can explain most of the observed variation in DMR. The frequency of slow hydroxylators in Sweden is very similar to that reported in other European studies. The debrisoquin metabolic phenotype seems to be extensively controlled by a monogenic system and not significantly influenced by environmental factors or age.

Genetic regulation of the kinetics of glucose-induced insulin release in man. Studies in families with diabetic and non-diabetic probands.

Insulin release and sensitivity were estimated from glucose and insulin curves obtained at a glucose infusion test performed on altogether 601 subjects belonging to 155 nuclear families. Ascertainment was through one of the parents, and 96 of the probands had diabetes with clinical onset after the age of 30 years, while 59 were healthy subjects. Three variables obtained by a computer model were analysed, i.e. the glucose regulation of insulin release by a direct stimulatory event (KI) and time-dependent modulatory events (KP) as well as insulin sensitivity (KG). Complex segregation analysis revealed that the variables are genetically regulated, but there was no evidence for a major locus. The children of the diabetics did not differ from those of the non-diabetics as far as insulin release is concerned.

Genetic and environmental determinants for lipoprotein concentrations in blood.

Path and segregation analyses have been performed on cholesterol and triglyceride contents of serum as well as on very low, low and high density lipoproteins in 78 Swedish nuclear families. The effect of environmental variables like alcohol and smoking on the concentrations of the different lipoproteins has been studied. Genetic heritability was 0.16-0.68 for the cholesterol fractions and 0-0.56 for the triglyceride fractions. No major gene was evident for any of the variables studied.

European collaborative study on prenatal diagnosis: mosaicism, pseudomosaicism and single abnormal cells in amniotic fluid cell cultures.

A report is given of the results of a European collaborative study on mosaicism, pseudomosaicism and single abnormal cells in amniotic fluid cell cultures. The mean frequency of cases with mosaicism was 0.10 per cent, with pseudomosaicism 0.64 per cent and with single abnormal cells 2.83 per cent in a series of 44 170 amniotic fluid samples. There was no significant difference between the colony (in situ) and the flask method with regard to the frequency of mosaicism. Pseudomosaicism and single abnormal cells were more frequent in cases studied with the flask method probably due to other factors than the method of cultivation of the cells. The frequency of maternal cell contamination was 0.17 per cent and the frequency of wrong sex assignment was 0.11 per cent. A more correct estimation is obtained if these frequencies are doubled. There was a considerable variation between laboratories with regard to the frequencies given above. One reason for this variation is that there are no sharp limits between mosaicism, pseudomosaicism and single abnormal cells. Thus the material contained cases diagnosed as having pseudomosaicism which turned out to be mosaics at birth and to have an abnormal phenotype. These cases were very rare but pose a definite problem in prenatal cytogenetic diagnosis.