(CA/TG) microsatellite sequences escape the inhibition of recombination by mismatch repair in Saccharomyces cerevisiae.

Sequence divergence reduces the frequency of recombination, a process that is dependent on the activity of the mismatch repair system. In the yeast Saccharomyces cerevisiae, repair of mismatches results in gene conversion or restoration, whereas failure to repair mismatches results in postmeiotic segregation (PMS). By examining the conversion and PMS in yeast strains deficient in various MMR genes and heterozygous for large inserts (107 bp) with either a mixed sequence or a 39 (CA/TG) repetitive microsatellite sequence, we demonstrate that: (1) the inhibition of conversion by large inserts depends upon a complex containing both Msh2 and Pms1 proteins; (2) conversion is not inhibited if the single-stranded DNA loop in the heteroduplex is the microsatellite sequence; and (3) large heteroduplex loops with random sequence or repetitive sequence might be repaired by two complexes, containing either Msh2 or Pms1. Our results suggest that inhibition of recombination by heterologous inserts and large loop repair are not processed by the same MMR complexes. We propose that the inhibition of conversion by large inserts is due to recognition by the Msh2/Pms1 complex of mismatches created by intrastrand interactions in the heteroduplex loop.

(CA/GT)(n) microsatellites affect homologous recombination during yeast meiosis.

One of the most common microsatellites in eukaryotes consists of tandem arrays of the dinucleotide GT. Although the study of the instability of such repetitive DNA has been extremely fruitful over the last decade, no biological function has been demonstrated for these sequences. We investigated the genetic behavior of a region of the yeast Saccharomyces cerevisiae genome containing a 39-CA/GT dinucleotide repeat sequence. When the microsatellite sequence was present at the ARG4 locus on homologous chromosomes, diploid cells undergoing meiosis generated an excess of tetrads containing a conversion of the region restricted to the region of the microsatellite close to the recombination-initiation double-strand break. Moreover, whereas the repetitive sequence had no effect on the frequency of single crossover, its presence strongly stimulated the formation of multiple crossovers. The combined data strongly suggest that numerous recombination events are restricted to the initiation side of the microsatellite as though progression of the strand exchange initiated at the ARG4 promoter locus was impaired by the repetitive sequence. This observation corroborates in vitro experiments that demonstrated that RecA-promoted strand exchange is inhibited by CA/GT dinucleotide tracts. Surprisingly, meiotic instability of the microsatellite was very high (>0.1 alterations per tetrad) in all the spores with parental and recombinant chromosomes.

Near normalization of final height with adapted doses of growth hormone in Turner's syndrome.

An adapted GH dose regimen was evaluated in 14 untreated patients with Turner's syndrome. The initial GH dose (0.7 U/kg.BW) was increased by 0.7 U/kg.BW, up to a maximum of 2.1 U/kg.BW, when growth velocity (GV) declined to less than 200% of the pretreatment level. These patients were compared to a group of 17 patients with similar initial characteristics, who received a fixed dose of 0.9 U/kg.BW GH. Tolerance to both GH regimens was excellent. The adapted GH doses only partially prevented the waning effect observed with conventional doses of GH, and the initial goal of doubling GV was only achieved in 42% of the 112 patient-semesters. Doubling the GH dose from 0.7 to 1.4 U/kg.BW increased the GV by 1.6 +/- 1.8 cm/yr (P < 0.006); increasing the GH dose from 1.4 to 2.1 U/kg.BW increased GV by 0.8 +/- 1.3 cm/yr (P = NS). The overall height gain during the 4-yr trial was 25.6 +/- 3.9 cm in the adapted dose group and 21.8 +/- 3.9 cm in the conventional group (P < 0.02). Final height (FH) results were obtained in 12 of 14 patients in the adapted dose group and all 17 patients in the conventional group and compared to the predicted FH using Lyon's method. The estimated height benefit was 10.6 +/- 3.8 cm in the adapted dose group compared to 5.2 +/- 3.7 cm in the conventional group (P < 0.01). Eighty-three percent of the patients in the adapted dose group had an FH superior or equal to -2 SD score for the general population compared to 29% in the conventional group. In conclusion, a marked increment in the GH dose in girls with Turner's syndrome associated with a relatively late age at introduction of estrogen therapy brought 83% of the patients into the lower range of the normal height distribution of the general population.

Pharmacological testing for the diagnosis of growth hormone deficiency.

Evaluation of growth hormone (GH) secretion using pharmacological GH stimulation tests (GHSTs) remains current practice, although the reliability of GHSTs has been questioned and many pitfalls have been pointed out. We have analysed all the 6,373 GHSTs which led to the initiation of GH therapy in 3,233 children treated in France from 1973 to 1989. Eleven different pharmacological tests were used, and 62 out of the 66 theoretical pairs of tests were used at least once. The most frequent combination of tests was used in 12.7% of patients. Reliability of GH peak measured by comparing the results of two tests in the same patient was poor, as measured by intraclass correlation coefficients (all under 0.8). Multivariate analysis identified several parameters positively or negatively associated with peak plasma GH. We believe that several of these factors (i.e. weight standard deviation score (SDS), genetic target height SDS and nature of the agent) identify biases in the diagnosis of GH deficiency (GHD). In addition, we re-evaluated GH secretion in 208 young adults formerly treated with GH for childhood onset GHD. Peak plasma was superior or equal to 10 ng/ml in 81% of patients with former idiopathic GHD. We conclude that the current use of GHSTs as well as the criteria for idiopathic childhood GHD should be questioned.

Growth hormone therapy for Turner syndrome: evidence for benefit.

Growth hormone (GH) is registered for children with Turner syndrome (TS) in several countries. Improving the final heights (FH) is certainly the most worthy goal of therapy, but evaluation of treatment effect is complicated by methodological difficulties. Several series of FH results have now been published, with estimated benefits ranging from 0-9.3 cm, as compared to predicted height before treatment. The majority of studies report height gains of less than 5 cm, but in these studies, GH was started at a relatively late age and used at low doses. Several approaches can be utilized to improve FH results in TS, including early initiation of GH therapy, increased or optimized GH dose regimens, or optimization of sexual steroid utilization.

Differences and similarities between various tandem repeat sequences: minisatellites and microsatellites.

Tandemly repetitive DNA sequences are abundantly interspersed in the genome of practically all eukaryotic species studied. The relative occurrence of one type of repetitive sequence and its location in the genome appear to be species specific. A common property of repetitive sequences within the living world is their ability to give rise to variants with increased or reduced number of repeats. This instability depends upon numerous parameters whose exact role is unclear: the number of repeats, their sequence content, their chromosomal location, the mismatch repair capability of the cell, the developmental stage of the cell (mitotic or meiotic) and/or the sex of the transmitting parent. It is now apparent that mutations in repetitive sequences are a common cause of human disease, including cancer and disorders which may exhibit a dominant mode of inheritance. Two mechanisms have been proposed to explain the instability of repetitive sequences: DNA polymerase slippage, which may account for the instability of short repeats and unequal recombination which reshuffles repeat variants and maintains repeat heterogeneity in minisatellites. The purpose of this review is to show that no general rule can explain the instability of repetitive sequence. Each sequence of repeats is under the influence of local and general biological activities that determine its level of instability.

[Parasitemia in Plasmodium falciparum malarial attacks in children]. / Parasitémie au cours des accès palustres à Plasmodium falciparum chez l'enfant.

In order to evaluate the predictive value of parasitaemia, this parameter was measured on admission in 69 Gabonese children aged from 3 to 13 years hospitalized for Plasmodium falciparum malarial attacks. Fourteen of these children had cerebral malaria, 5 had isolated convulsions and 50 had uncomplicated attacks. The parasitaemia values measured were compared with those found in asymptomatic children of the same age range carrying trophozoites. There were no significant differences in mean parasitaemia count between the 3 types of malarial attack, and only the asymptomatic carriers had significantly lower counts. However, the wide scattering of individual values within each group indicated that simple measurement of parasitaemia is not discriminative enough to predict the course of malarial attacks in children living in endemic regions. In particular, malarial attacks with very low or very high parasitaemia value are possible, but similar values are found in asymptomatic carriers.

[Malaria and hemoglobin S: interactions in African children]. / Paludisme et hémoglobine S: interactions chez l'enfant africain.

Among 300 cases of Plasmodium falciparum malaria attacks explored in Gabon, the proportion of homozygous (SS) or heterozygous (AS) sickle-cell patients was 6.2 percent in 206 ordinary attacks and 3.2 percent in 94 cerebral malaria attacks, and 23.2 percent in the general population. On the other hand, asymptomatic carriage, as detected in 98 children by thin blood films in school screening, was as frequent in the SS or AS infantile population as in the general population. These data show that haemoglobin S protects effectively, although not entirely, against severe attacks of P. falciparum malaria. The incidence of anaemia and vaso-obstructive crisis in malaria-infested sickle-cell patients suggests that subclinical carriage of haematozoa may worsen the course of sickle-cell disease, and this must be taken into account when planning treatment.

Efficacy, safety and acceptability of halofantrine in the treatment of acute Plasmodium falciparum malaria in African children (Gabon).

Halofantrine chlorhydrate 2 per cent suspension was given to 50 children (mean age 6.2 years in a dose of 8 mg/kg three times a day as a single day treatment. The children were born and lived in Gabon, where malaria transmission is continuous. They all had acute Plasmodium falciparum malaria. The children were kept in hospital for 5 days, and regularly followed over a 15-day period. The 50 children were cured and efficacy was evaluated as good in 44 cases, and excellent in six cases, as judged by improvement in their clinical signs and parasitaemia. Two criterias were considered in the evaluation of efficacy: clearance of parasitaemia (mean day 4), fever clearance (mean hour 24). There were two cases of persistences of parasites at day 15 with a very low parasitaemia rate. Tolerance to halofantrine was good from a clinical and biological point of view. Acceptability was excellent in all cases. Halofantrine 2 per cent suspension is a good alternative in the treatment of acute Plasmodium falciparum malaria in children, especially with the present situation of multidrug-resistant strains in Central Africa.

Influence of intestinal parasitism on lactose absorption in well-nourished African children.

Hydrogen breath tests were performed in Gabon (Central Africa) after a loading dose of lactose in 67 well-nourished African children (50 with intestinal parasites and 17 unparasitized) and in 18 unparasitized young adults. All had normal nutritional status, and none had diarrhea or digestive symptoms. Parasites that were found included Ascaris lumbricoides in 76% of the parasitized children, Trichuris trichiura in 58%, Giardia in 24%, Entamoeba histolytica in 20%, Schistosoma intercalatum in 16%, and Necator Americanus in 14%. A similar proportion of parasitized (64%) or unparasitized (62.8%) subjects were lactose malabsorbers. Giardia infection was associated with a higher, but not significantly different, proportion of lactose intolerance (10 of 12, 83.3%). The presence of infection with A. lumbricoides or T. trichiura did not increase the percentage of lactose malabsorption. These data indicate that a decrease of lactase activity in well-nourished African children is not related to the presence or the importance of Ascaris or other intestinal parasites if the nutritional status is normal.

[Placental transfer of tetanus antibodies and protection of newborn infants]. / Transfert placentaire des anticorps antitétaniques et protection du nouveau-né.

Total IgG and tetanus antibodies were evaluated in 2 series of mother-child pairs: 50 in Paris and 134 in Africa. All pregnancies had been normal and birth weights greater than 3 kg. Cord blood mothers tetanus antibodies ratios were 1.5 in Paris and 0.98 in Libreville (p less than 0.01) respectively. Some African children were not protected, either due to the lack of response of their mothers to immunization (2.2%) or to an insufficient antibodies transplacental transport (2.9%), or to the lack of immunization of mothers (5.9%). On the contrary, all European children were protected, in spite of low maternal antibody levels. Likewise, in Paris cord blood IgG level was 12.24 g/l vs 9.42 in mothers (cord blood/mother ratio: 1.34) and in Africa 18.4 g/l in cord blood and 22.3 g/l in mothers (cord blood/mother ratio: 0.88; p less than 0.01). The correlations between maternal IgG levels and placental transfer rates indicate that the transplacental active transfer is limited by common high IgG levels in Africa, thus contributing to a decrease in protection of neonates, especially against tetanus in which humoral responses predominate.

[Intestinal parasites and lactose malabsorption]. / Parasites intestinaux et malabsorption du lactose.

Breath-test was performed for diagnosis of lactose malabsorption in 50 Gabonese children of normal nutritional status, aged 5 to 15 years, with parasites in stools, but without diarrhoea or digestive symptoms. Control group was unparasitized and consisted of 17 children and 18 young adults living in the same area. Parasites discovered by stool examination were Ascaris lumbricoides in 76% of parasitized children, Trichuris trichiura in 58%, Giardia in 24%, Entamoeba histolytica in 20%, Schistosoma intercalatum in 16% and Necator Americanus in 14%. Children were given a 10 g lactose load and adults 20 g. Lactose malabsorption was discovered in 64% of parasitized patients and in 63% of unparasitized. Ten of 12 (83.3%) of Giardia infected children had a lactose malabsorption (no significant difference). These data show that decrease of lactase activity in African children is not related to the presence or to the importance of intestinal parasitism, except for Giardia infestation, if nutritional status is normal.

[Use of a fermented powdered milk in malnourished or lactose intolerant children]. / Utilisation d'un lait fermenté en poudre chez l'enfant malnutri ou intolérant au lactose.

Lactase deficient subjects, who form the bulk of the world population, absorb yogurt lactose because the bacteria used for fermentation produce beta-galactosidase. From a milk fermented by these bacteria and dried by a temperature-controlled process a power could be obtained which possess residual lactase activity but, unlike yogurt, does not need storage at low temperature. The lactose of this fermented powdered milk is perfectly absorbed, as proved by hydrogen respiratory tests performed in 35 lactose intolerant African subjects living in isolated villages. In 25 malnourished children under 3 years of age, this milk allowed renutrition without inducing diarrhoea--a result which could not have been obtained with ordinary milk in two-thirds of the cases. This type of food is potentially valuable to feed the large population of the third world.

Feeding lactose-intolerant children with a powdered fermented milk.

Fresh yogurt has been proposed as a milk substitute for lactase-deficient patients. We investigated the possibility that a dried, low-fat milk fermented by yogurt microorganisms would be effective. Processing of a fermented milk by spray-drying led to a powder with persistence of lactase activity (11.7 units/g) without storage at 4 degrees C and stable at room temperature (20-23 degrees C). The tolerance and absorption of 10.5 g of lactose in a volume of 150 ml was studied in 25 Gabonese lactase-deficient children aged 5-14 years in the form of a standard humanized milk formula followed 1 week later by the powdered fermented milk formula. Results of the breath hydrogen test showed that in 24 of 25 cases, lactose absorption was normal with a maximal rise of hydrogen over baseline of under 13 ppm after ingestion of the powdered fermented milk. The rise was above 20 ppm in the 25 children with the same load of lactose in the form of the standard formula and one-third had symptoms of lactose intolerance. This powdered fermented milk preparation should be considered as a valid approach in programs of nutritional support targeted to countries with a high prevalence of lactase deficiency.

Milk lactose malabsorption in Gabon measured by the breath hydrogen test.

It is usual to consider that the greatest part of the black African population is lactose intolerant. Also, milk lactose malabsorption was studied by a breath hydrogen technique in 87 Gabonese children and 20 Gabonese adults (central Africa). The prevalence of malabsorption was 64.2% in rural schoolchildren, 65% in the urban hospitalized, and 60% in adults. Twelve children and six adults had clinical symptoms after a lactose load. All subjects were Bantus, with no tradition of consuming dairy products. These data must be considered in programs of nutritional support in Africa.

Giardiasis and breast-feeding in urban Africa.

PIP: The protective role of breastfeeding against Giardia lamblia, a protozoan parasite endemic in Central Africa, was assessed through an analysis of stool samples from 400 infants aged 1 week-24 months in Libreville. Stool samples were collected during both the rainy and dry seasons in 1985 and 1986. At the time of stool collection, 237 infants were breastfed and 163 were bottle-fed (the mean weaning age among the 123 infants in the latter group who had at 1 point been breastfed was 8.2 months). The percentage of infants infected with cysts or trophozoites of Giardia was 1.2% in the exclusively breastfed group, 1.32% among infants who were partially breastfed (at least 2 feedings/day) and 14.7% in the bottle-fed group. The same pattern persisted when the data were grouped by age. In the 0-5 month age group, Giardia infection was found in 2.2% of the breastfed infants compared with 9.1% of the bottle-fed infants. In the 6-11 month age group, these percentages were 0 and 11.4%, respectively, while they were 2.2% and 17.6%, respectively, in the 12-23-month age group. There were no significant differences in the rate of giardiasis infection in the mothers of breastfed, partially breastfed, and bottle-fed infants in this study. These findings confirm an in vivo protective effect of human milk in Giardia infection. Of concern is the declining rate of breastfeeding in African cities, which can be expected to contribute to raising the rates of early symptomatic giardiasis and consequently the risk of malnutrition.^ieng

[Breast-feeding and intestinal parasites]. / Allaitement maternel et parasites intestinaux.

The extent of intestinal parasitic infection was determined using 4 methods of fecal examination in 400 Gabonese infants aged 0.5 to 24 months (86 exclusively and 151 partially breast-fed and 163 artificially fed) and in 170 of their mothers in an African urban community. Parasitic prevalence was the same in the stools of the mothers from the 3 infant groups, providing evidence for the same level of exposure to parasites in all infants. Exclusively and partially breast-fed infants excreted parasites in numbers significantly lower than artificially fed infants of the same ages, during the first and the second years of life. This antiparasitic activity of human milk concerned mostly Giardia and ascaris, was not exclusively due to a decreased exposure to parasites in breast-fed infants and did not seem exclusively antibody-mediated; the role of lipids is possible.

[Intestinal parasitic colonization and protein-caloric malnutrition]. / Colonisation parasitaire intestinale et malnutrition protéino-calorique.

Intestinal parasitic infection was determined by fecal examination for parasites with several complementary methods in 380 young Gabonese infants aged 6 to 24 months (190 with normal weights and 190 with malnutrition, matched for age). Trichuris trichiura, Ascaris lombricoides, Giardia intestinalis, Entamoeba histolytica and Strongyloides stercoralis were the most prevalent parasites, without any difference between well-fed infants and patients with malnutrition. The higher prevalence of Strongyloides stercoralis in protein energy malnutrition might be related to a methodologic problem. However, more than 20% of diarrheas in infants with severe malnutrition were dramatically improved by specific treatment of S. stercoralis or Giardia with thiabendazole or metronidazole.