Cytogenetic and molecular-cytogenetic studies of Rett syndrome (RTT): a retrospective analysis of a Russian cohort of RTT patients (the investigation of 57 girls and three boys).

Rett syndrome (RTT) is a severe neurodevelopmental disorder with an incidence of 2.5% in mentally retarded girls in Russia. We have performed cytogenetic studies of 60 patients (57 girls and three boys) with a clinical picture of RTT, selected according to the criteria for diagnosis of RTT defined by B. Hagberg et al. in 1996. Collection of DNA samples and fixed cell suspensions of RTT patients (37 girls and two boys) and their parents (27 patients) was established for molecular studies, for example analysis of MECP2 mutations in a Russian cohort of RTT patients. Among 60 patients 57 girls with a clinical picture of RTT had normal female karyotype (46,XX), one boy had normal male karyotype in peripheral lymphocytes (46,XY) and two boys had a mosaic form of Kleinfelter's syndrome (47,XXY/46,XY) in peripheral lymphocytes or muscle cells (with MeCP2 mutation R270X). Twenty-four mothers and parents of RTT girls had normal karyotype, two mothers had mosaic forms of Turner syndrome (45,X/46,XX) and one had mosaic karyotype (47,XX,+mar/48,XXX,+mar). We analyzed chromosome X in lymphocytes of 57 affected girls with a clinical picture of RTT using the 5-bromo-2'-deoxyuridine+Giemsa staining technique. A specific type of inactive chromosome X (so-called type 'C') with unusual staining of chromatin in the long arm of chromosome X was found in 55 (from 57) girls with RTT. This technique was positively used for presymptomatic diagnosis of RTT in five girls in earlier stages of the disease. We believe that the phenomenon of altered chromatin conformation in inactive chromosome X could be used as a laboratory test for preclinical diagnosis of the RTT.

[Current methods of molecular cytogenetics in pre- and postnatal diagnosis of chromosome aberrations]. / Sovremennye metody molekuliarnoi tsitogenetiki v pre- i postnatal'noi diagnostike khromosomnoi patologii.

Progress in prevention of chromosome aberrations is due to utilization of molecular cytogenetic diagnostic methods. The purpose of this trend of clinical cytogenetics is development and utilization of new highly effective methods for analysis of chromosome aberrations. Molecular cytogenetic methods (fluorescent in situ hybridization-FISH) are used for pre- and postnatal identification of chromosome aberrations in mentally retarded children and congenital diseases. These studies are carried out after classical cytogenetic analysis, if it proves to be of no avail. FISH diagnosis pre- and postnatally detects autosomal trisomy, gonosome aneuploidy (including mosaic forms), marker chromosomes, structural chromosome aberrations, including fragile X chromosome syndrome. Rapid (15-30 min) FISH with an original collection of centromere, telomere, and site-specific DNA probes (plasmid, cosmid, PAC and YAC clones) is recommended for molecular cytogenetic diagnosis. FISH diagnosis is an effective complex of methods for pre- and postnatal identification of chromosome aberrations and a necessary supplement to classical cytogenetic diagnosis. Molecular studies of chromosome aberrations are significant for theoretical and applied studies, for they help detect patients with specific chromosome syndromes from a vast group of children with undifferentiated mental retardation and congenital diseases.

Rapid chromosomal analysis of germ-line cells by FISH: an investigation of an infertile male with large-headed spermatozoa.

A rapid fluorescence in-situ hybridization (FISH) technique was used for direct chromosomal analysis on germ cells from an infertile male with large-headed spermatozoa. The interphase chromosomes were fluorescently-labelled using an extremely bright cyanine dye during a 5-15 min FISH procedure. Germ cells were analysed using a battery of chromosome-specific DNA probes in several consecutive rapid FISH experiments. It was found that the majority of large-headed spermatozoa contained a diploid chromosome number probably due to errors in meiosis I or II divisions, whereas the majority of spermatozoa with normal sized heads are haploid and may be utilized for selective in-vitro fertilization procedures. Rapid FISH may be useful for the detection of major chromosomal aneuploidies in germ cells as an alternative technique to standard or multicolour FISH, and may find an additional application for the chromosomal analysis of human preimplantation embryos.