title: [Principles of DNA diagnosis].
abstract: In an ever-increasing number of the more than 4000 known genetic diseases with Mendelian inheritance, the geneloci have been mapped. In such cases it is possible to predict by DNA techniques whether or not family members are carriers of the mutation and risk having affected children. Using the same methods, disease can also be predicted prenatally from chorionic villi biopsies (CVS) as early as the ninth week of pregnancy. With some diseases it is possible to analyze the DNA of the mutation directly, whereas in others closely linked polymorphic DNA markers have to be analyzed in order to distinguish the mutationbearing chromosome from the one with the normal allele. The techniques of diagnostic DNA investigations are now standard procedures in medical genetic laboratories and are performed almost routinely for many diseases: The total (genomic) DNA, with a length of 3 x 10(9) base pairs (bp), is extracted from cells, mainly leukocytes from EDTA blood samples, then digested by restriction endonucleases into smaller fragments with a length of approx. 10(3) to 10(4) bp. The fragments are separated according to their lengths by agarose gel electrophoresis, then transferred to nitrocellulose ("Southern Blot") and made "single-stranded" by denaturation. The fragment in question can now be recognized by a specific gene probe with a homologous base sequence (hybridization). Since the probe is slightly radioactive, the hybridized genomic DNA fragment is recognized by autoradiography, and its length determined by the relative position it reached during electrophoresis. These analyses can be carried out simultaneously for different DNA fragments within and outside the gene locus.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Medizinische Genetik der Universitäts-Kinderklinik, Bern.
authors.forename: H
authors.initials: H
authors.lastname: Moser
mesh_terms: D000328:Adult; D002648:Child; D002869:Chromosome Aberrations / Q000175:diagnosis* / Q000235:genetics; D025063:Chromosome Disorders; D003550:Cystic Fibrosis / Q000175:diagnosis* / Q000235:genetics; D004247:DNA / Q000235:genetics*; D004252:DNA Mutational Analysis; D005260:Female; D005808:Genes, Recessive; D006580:Genetic Carrier Screening; D006801:Humans; D009136:Muscular Dystrophies / Q000175:diagnosis* / Q000235:genetics; D010375:Pedigree; D011247:Pregnancy; D011296:Prenatal Diagnosis; D012307:Risk Factors; D012729:Sex Chromosome Aberrations / Q000175:diagnosis* / Q000235:genetics; D014960:X Chromosome
chemical_list: D004247:DNA
vernacular_title: Grundlagen der DNA-Diagnostik.