Recent advances in human molecular genetics
Rinsho Byori. Japanese Journal of Clinical Pathology 38(10): 1093-1100
The haploid nucleus of a human cell contains 3 X 10(9) base pairs. Organized in linear duplex, this DNA would stretch out to a length of some 90 cm. Thus, organization of chromosomes has been a major subject for pioneer cytogenetists. Long lasting controversies on the strandedness of chromosomes, together with newly developed banding techniques, led us to molecular cytogenetics. Next, the discovery of reverse transcriptase, restriction endonucleases, and other recombinant DNA methods have enabled us to isolate and characterize genes from any organism and to determine the DNA sequences and any encoded protein sequences. These new technologies have already helped us to understand many inherited diseases at a molecular level. In sickle cell anemia, thalassemia and in other mendelian disorders we can know their molecular defects by examining the DNA from peripheral leukocytes, without the need for complex biochemical assays or biopsies. Southern blot analysis using restriction endonuclease and a probe is a basic tool for molecular diagnosis. cDNA or DNA fragments are used as probes. Recently, synthesized oligonucleotide probes are available, if the DNA sequence of a gene is determined. In addition, restriction fragment length polymorphisms (RFLPs), play a very important role in the molecular diagnosis. Linkage analysis using RFLPs linked to the gene locus of a certain disease also permits the detection of the patients and carriers within families with genetic diseases of unknown cause. Starting with the genetic map and physical map, genes for cystic fibrosis and Duchenne muscular dystrophy have recently been isolated and cloned.