The concepts of genotypes and phenotypes are a crucial context for understanding genetic disease. Genetic diseases can impact any of the five protein functions: catalysis (enzymes); binding; transport; chemical machines; and defense. Enzymopathies are diseases due to enzyme defects -- the most thoroughly studied enzymopathy is undoubtedly phenylketonuria. An example of a disease affecting receptor proteins is familial hypercholesterolemia. The most prevalent disorder of structural proteins is Duchenne muscular dystrophy.
Major obstructions to treating single-gene diseases are that: the gene function (or the gene itself) might be unknown; prenatal damage might be irreversible; and severe phenotypes are difficult to treat. Active research and carrier screening address the first two issues, while nurturing any sort of residual activity helps ameliorate the third.
|Mutant Gene||Modification of somatic genotype (transplantation or gene therapy) or alteration of gene expression (administration of transcription factors).|
|Mutant mRNA||RNAi to degrade mutant mRNA.|
|Mutant Protein||Protein replacement; stimulation of residual function.|
|Biochemical Dysfunction||Dietary restriction; pharmacologic treatment.|
|Clinical Phenotype||Dietary Restrciciton (of improperly processed chemicals) Replacement (of essential metabolites) Diversion (usage of alternative pathways to avoid accumulation -- depletion of bile acids to promote conversion of LPL, or ligation of ammonia into a chemical that is secreted in urine). Inhibition of synthesis of the chemical which accumulates Depletion, such as drawing of blood that is saturated with iron. Surgery, and indirect medical treatment (organ support for Alzheimer's patients).|
|Familial||Genetic counseling and screening.|
|Derived from Nussbaum, McInnes & Willard: Genetics in Medicine, 7th ed. Philadelphia, Saunders, 2007. (pg 397)|