Saturday 19 July 2003
IN 2006, more than 1,800 genes are known to cause hereditary disorders in humans.
On 2 February 2000, OMIM reached 1000 gene entries containing at least one allelic variant (AV) identified as the cause of, or associated with, a recognizable human phenotype.
|-||Recessive monogenic diseases||Dominant monogenic diseases||Polygenic diseases|
|Predictive power of mutation analysis||Almost 100%||Strong*||Weak|
|Onset||Fetus, child, adolescent||Adult||Adolescent, adult|
|Molecular genetic approaches||Direct exon sequencing of known disease genes||Direct exon sequencing of known disease genes||Only assignment of relative risk possible|
|Frequency||< 1 in 40 000 (rare)||< 1 in 1000 (rare)||< 1 in 5 (frequent)|
|Data usually derived from||Gene mapping and gene identification||Gene mapping and gene identification||Genome-wide association studies (GWAS)|
|Confirmation in animal model||Very feasible||Feasible||Difficult|
chromosomal diseases by chromosomal anomalies
- monogenic diseases (mendelian diseases)
- oligogenic diseases
- polygenic diseases (complex inheritance diseases, diseases with multifactorial inheritance)
chromosomal rearrangements (chromosomal diseases)
genic mutations (genic diseases)
Monogenic diseases include many relatively uncommon conditions, such as storage disorders and inborn errors of metabolism, all resulting from single-gene mutations of large effect. Because most of these follow the classic mendelian patterns of inheritance, they are also referred to as mendelian disorders.
Multifactorial diseases include some of the most common diseases of humans, such as hypertension and diabetes mellitus. They are called multifactorial because they are influenced by both genetic and environmental factors. The genetic component involves the additive result of multiple genes of small effect; the environmental contribution may be small or large, and in some cases, it is required for the expression of disease.
The third category includes diseases that result from genomic or chromosomal mutations and are therefore associated with numerical or structural changes in chromosomes
Single-gene diseases with nonclassic patterns of inheritance
To these three well-known categories must be added a heterogeneous group of single-gene disorders with nonclassic patterns of inheritance. This group includes disorders resulting from triplet repeat mutations, those arising from mutations in mitochondrial DNA, and those in which the transmission is influenced by genomic imprinting or gonadal mosaicism. Diseases within this group are caused by mutations in single genes, but they do not follow the mendelian pattern of inheritance.