Increased methotrexate-induced chromosome breakage in patients with free trisomy 21 and their parents

Pathogenesis of mental deficiency in trisomy 21

In trisomy 21, pathogenesis of mental retardation is still poorly understood although the knowledge of the genic content of chromosome 21 is steadily increasing. Short of discovering how to silence selectively one of the 3 chromosomes 21, no rational medication can be envisaged before pathogenesis has been unraveled, at least partially. A biochemical scheme of impairment of mental efficiency is presented. Secondarily, the possible deleterious effects of a given gene overdose are discussed. Cu/Zn SOD, cystathionine beta synthase, S 100 beta protein, phosphofructokinase, purine synthesis and adenosine pharmacology, thyroid disturbance, and elevated TSH with low rT3 as well as biopterine metabolism interferences are reviewed. It is observed that the metabolic paths controlled by these genes, although unrelated at first glance, are in fact tightly related by their effects, just as if synteny was in some way related to biochemical cooperation or mutually controlled regulation. Experiments in vitro have demonstrated a peculiar sensitivity of trisomic 21 lymphocytes to methotrexate. From this starting point, systematic research of special sensitivities has begun. Clinical observations and relevant statistical methods allow study of the speed of mental development under various medications. The interest of regulating thyroid metabolism, when needed, is exemplified. Reequilibration of monocarbon metabolism is discussed and the seemingly favourable effect of folinic acid medication in pseudo-Alzheimer complication is presented.

Micronucleus incidence and their chromosomal origin related to therapy in acute lymphoblastic leukemia (ALL) patients: detection by micronucleus and FISH techniques

Micronucleus assay and dual color-fluorescence in situ hybridization (DC-FISH), using centromere-specific and whole chromosome-specific painting probes, are considered a useful screening test to determine the incidence of micronucleus, their origin and contents. The patients with acute lymphoblastic leukemia (ALL), who had undergone chemotherapy, were analysed before and after treatment with vincristine, methotrexate, daunomycin, prednisone, and asparaginase. The incidence of micronuclei after the antileukemic agent treatment was significantly higher than before the treatment. Application of DC-FISH using a combination of whole chromosome-specific painting probes and the same chromosome-specific alpha-satellite centromeric probe showed that there were no significant differences in the micronucleus incidence for any specific chromosome (chromosomes 7, 8, 11, 17, X, and Y). There were no significant differences between the incidence of centromere-positive micronuclei and the incidence of centromere-negative micronucleus. We concluded that antileukemic agents induced the somatic genetic damage but this damage is not related to any specific chromosome studied.

Chromosome sensitivity to bleomycin in G2 lymphocytes from Down syndrome patients

Several studies have demonstrated that lymphocytes from patients with Down syndrome (DS) exhibit an increased frequency of chromosome aberrations when they are exposed to ionizing radiation or to chemicals at the G0 or G1 phases of the cell cycle, but not at G2, when compared to normal subjects. To determine the susceptibility of DS lymphocytes at G2 phase, bleomycin, a radiomimetic agent, was used to induce DNA breaks in blood cultures from 24 Down syndrome patients. All the patients with DS showed free trisomy 21 (47,XX + 21 or 47,XY + 21). Individuals that showed an average number of chromatid breaks per cell higher than 0.8 were considered sensitive to the drug. No control child showed susceptibility to bleomycin, and among the 24 patients with DS, only one was sensitive to the drug. No significant difference was observed between the two groups, regarding chromatid break frequencies in treated G2 lymphocytes. The distribution of bleomycin-induced breaks in each group of chromosomes was similar for DS and controls. No significant difference was found in the response to bleomycin between male and female subjects. Probably, the main factor involved in chromosome sensitivity of lymphocytes from patients with DS is the phase of the cell cycle in which the cell is treated.

Fragile site induction by aphidicolin may be increased in parents of neuroblastoma patients

We recently demonstrated an increased expression of fragile sites, induced by aphidicolin, in lymphocytes of neuroblastoma patients. We have now extended our studies to parents of affected children with neuroblastoma to verify if this characteristic may be genetically transmitted. We have examined 20 families. In most of them, the hypersensitivity to aphidicolin was found in the affected child and in at least one parent. Moreover, some of the parents showed an increase in the expression of the fragile sites 1p32, 1p13, or both that are preferentially expressed in neuroblastoma patients. The possible relations between the hypersensitivity to aphidicolin and the inheritance of predisposition to neuroblastoma must be clarified.