The human genome: the nature of the enterprise

Unravelling the genetics of inherited retinal dystrophies: Past, present and future

The identification of the genes underlying monogenic diseases has been of interest to clinicians and scientists for many years. Using inherited retinal dystrophies as an example of monogenic disease we describe the history of molecular genetic techniques that have been pivotal in the discovery of disease causing genes. The methods that were developed in the 1970's and 80's are still in use today but have been refined and improved. These techniques enabled the concept of the Human Genome Project to be envisaged and ultimately realised. When the successful conclusion of the project was announced in 2003 many new tools and, as importantly, many collaborations had been developed that facilitated a rapid identification of disease genes. In the post-human genome project era advances in computing power and the clever use of the properties of DNA replication has allowed the development of next-generation sequencing technologies. These methods have revolutionised the identification of disease genes because for the first time there is no need to define the position of the gene in the genome. The use of next generation sequencing in a diagnostic setting has allowed many more patients with an inherited retinal dystrophy to obtain a molecular diagnosis for their disease. The identification of novel genes that have a role in the development or maintenance of retinal function is opening up avenues of research which will lead to the development of new pharmacological and gene therapy approaches. Neither of which can be used unless the defective gene and protein is known. The continued development of sequencing technologies also holds great promise for the advent of truly personalised medicine.

Isolation of a large number of novel mammalian genes by a differential cDNA library screening strategy

As part of the ongoing human and mouse genome projects, the aim of this study was to isolate novel, previously uncharacterized, genes from mouse testis. Two approaches were compared for their effectiveness in isolating novel genes: random, vs differential, complementary DNA (cDNA) cloning methods. In the differential approach, only the cDNA clones containing rare sequences (as determined by preliminary clone hybridization) are further analyzed; in the random approach, cDNA clones are isolated at random from the cDNA library. More than two hundred cDNA clones altogether were analyzed, using a PCR-mediated amplification and sequencing strategy. A comparison of these sequences to nucleic acid and protein sequence databases, revealed that 84% of the isolated rare cDNA clones represented new, previously uncharacterized mouse genes. In contrast, less than 63% of the cDNA clones isolated at random from cDNA libraries, contained novel genes. Thus, the probability of isolating new, previously uncharacterized, mammalian genes from cDNA libraries can be markedly improved by focusing efforts on clones containing rare sequences.