Measuring the kinetics of biomolecular recognition with magnetic colloids.

We introduce a general methodology based on magnetic colloids to study the recognition kinetics of tethered biomolecules. Access to the full kinetics of the reaction is provided by an explicit measure of the time evolution of the reactant densities. Binding between a single ligand and its complementary receptor is here limited by the colloidal rotational diffusion. It occurs within a binding distance that can be extracted by a reaction-diffusion theory that properly accounts for the rotational Brownian dynamics. Our reaction geometry allows us to probe a large diversity of bioadhesive molecules and tethers, thus providing a quantitative guidance for designing more efficient reactive biomimetic surfaces, as required for diagnostic, therapeutic, and tissue engineering techniques.

Fetoplacental chromosomal discrepancy.

Chorionic villus sampling is now an acceptable alternative to second trimester amniocentesis. Several reports have raised concerns about the occurrence of discrepancies between the chorionic villi and fetal chromosomal constitution, which adds multiple diagnostic complexities to the process of prenatal genetic counselling. We report on a series of 26 cases in which fetoplacental discrepancies have occurred. The chromosomal aberration was exclusively confined to the placenta in 21 cases. Twice the identical aberration was also observed in amniotic fluid with variant range of aneuploidy. The chromosomal abnormality was found in amniotic fluid and fetal blood samples in two cases, and was absent in chorionic villi. One case had very unusual cytogenetic findings as two different non-mosaic chromosomal abnormalities were identified separately in the placenta and amniocytes. Among the 21 gestations with confined placental abnormal karyotype, three cases of intrauterine growth retardation were identified. Of six cases evaluated for uniparental disomy, four demonstrated biparental inheritance. These findings support a positive correlation between placental aneuploidy and abnormal fetal development. They also emphasize the importance of further DNA analysis whenever discrepant karyotype findings between the placenta and amniocytes are identified.

Unexpected inheritance of the (CGG)n trinucleotide expansion in a fragile X syndrome family.

The fragile X syndrome is the most frequent cause of inherited mental retardation. CGG repeat alleles are usually classified as normal, premutation, or full mutation based on the length of this triplet in the 5' untranslated region of the FMR1 gene. The pattern of inheritance follows a two-stage intergenerational process in which the premutation evolves into the full mutation. Some reverse mutations have been described, but they appear to be very rare. We describe a family in which a mother of two affected males herself carried a full mutation. Surprisingly, her clinically normal daughter, initially considered to be a carrier by linkage analysis, carried a very short premutation. Findings from our family study corroborate the hypothesis that the expansion during female transmission could be a postzygotic event and raise the problem of mosaicism.

Prenatal diagnosis of Fryns' syndrome.

We report on a new case of ultrasonographic prenatal diagnosis of Fryns' syndrome during the second pregnancy of a young woman whose first child died 90 min after birth and was diagnosed as having this autosomal recessive condition. The feasibility of diagnosis in utero and timing in the phenotypic expression of this multimalformation syndrome are discussed.

[Fragile X syndrome: current knowledge]. / Le syndrome du chromosome X fragile: connaissances actuelles.

Fragile X syndromes is a disease characterized by the association of mental retardation and dysmorphic features to a fragile site on Xq27-3. It is a frequent genetic disorder (1 in 1,500 males) recognized only 20 years ago but remaining difficult to understand, because its transmission among generations does not correspond to the classical model of recessivity linked to chromosome X. In fact, carrier females can express the disease and transmitting males can be normal. With DNA probes, molecular biology has contributed to genetic counselling and prenatal diagnosis. Restriction polymorphisms have long been used to study the inheritance of fragile X syndrome and DNA markers' analysis improved risk estimates for carriers. From a clinical viewpoint, there was a need for more closely linked probes to help in prenatal diagnosis and to assess carrier status and hence reduce risk of recombination. In 1991, new probes allowed direct diagnosis of the Fra (X) mutation and a gene was sequenced. Nevertheless the understanding of the mechanism involved in the underlying mutation is still unknown. Geneticists, cytogeneticists and biologists must collaborate further to elucidate the fragile site mystery.

Fragile X syndrome in an extended family with special reference to an affected male with Klinefelter syndrome.

We report on a large family (4 generations), with 77 studied individuals, 9 mentally retarded males, and one affected female with fragile X syndrome [fra(X)]. The analysis of 6 flanking polymorphic DNA markers showed that the affection is transmitted, through the carrier daughters to the grandsons and the greatgrandsons and that the great-grandfather is a transmitting male. This observation led us to question the importance of these clinically normal males, who are nonexpressing carriers and termed transmitting males. One propositus, described as a mentally retarded young man, had inherited identical restriction polymorphisms from his mother. Chromosome analysis showed a Klinefelter syndrome, with a fragile site in 18% of the cells leading to the conclusion that the nondisjunction occurred at the first stage of the maternal meiosis.

Lipid peroxidation and benzo[a]pyrene activation to mutagenic metabolites: in vivo influence of vitamins A, E and C and glutathione in both dietary vitamin A sufficiency and deficiency.

Rats fed with either a sufficient-vitamin A or a vitamin A-free diet were pretreated with 750 mg/kg body weight of retinyl palmitate, alpha-tocopherol acetate, ascorbic acid or glutathione. Benzo[a]pyrene (BaP) metabolism and BaP-induced mutagenesis in Salmonella typhimurium TA98 were investigated and related to lipid peroxidation activities in postmitochondrial (S9) liver fraction. The microsomal mixed-function oxidase activities were decreased by vitamin A deficiency and weakly affected by scavenger treatment. The rate of lipid peroxidation of microsomal membranes was unaffected by vitamin A deficiency because of decreased polyunsaturated fatty acids and increased vitamin E contents. However, lipid peroxidation was decreased by pretreatment with fat-soluble vitamins (chiefly vitamin E) and increased by ascorbic acid. Within each experimental group both BaP metabolism and BaP mutagenic activity were closely correlated with the rate of lipid peroxidation. In vitamin A deficiency, the increased BaP metabolism and mutagenicity could be related to a decrease in cytosolic contents of scavengers (vitamin A and glutathione). In Ames test conditions, the free radical pathway became a route for BaP metabolism and thus the BaP activation to mutagenic metabolites is related to the cellular status in free radical scavengers.

Study of a family with a fragile site of the X chromosome at Xq27-28 without mental retardation.

The fragile site Xq27-28 was observed in several individuals of a large family. It is expressed at a high frequency among the carrier females, even as adults, and in one clinically normal male. None of the members of this family is affected with the mental retardation normally linked to this fragile site. Cytogenetic and flanking DNA marker polymorphism studies suggest a possible dissociation between the fragile site and clinical expression of the disease.

Trisomy 21q223 and Down's phenotype correlation evidenced by in situ hybridization.

Two cases of trisomy 21q223 with the Down's phenotype were analysed by in situ hybridization with specific probes previously located in the sub-bands 21q221 (SOD-A) and 21q223 (BCEI and COL6A). These studies give evidence that the clinical picture of Down's syndrome is at least to a great extent correlated with trisomy for the 21q223 band.

[Balanced chromosome rearrangements with abnormal phenotype]. / Remaniements chromosomiques équilibrés à phénotype anormal.

27 cases in which apparent balanced chromosomal rearrangements (reciprocal and translocations and pericentric inversions) are associated with phenotypic abnormalities are reported and compared with the previous published cases. Almost all patients display mental retardation and a non specific dysmorphism. Genetic counseling is different whether the abnormality is inherited or de novo. When an unexpected structural rearrangements is found in fetal cells, the attitude depends on the results of the parent's chromosomal study.

Monosomy 21: a new case confirmed by in situ hybridization.

A new case of total monosomy 21 in a newborn is described. The diagnosis was first made using the cytogenetic data; it was then confirmed by the dosage of copper-superoxide dismutase (SOD-1) which showed a 50% decrease. In situ hybridization with a probe previously assigned to chromosome 21 was used to rule out the possibility of a partial monosomy with an unbalanced reciprocal translocation.