genetic diseases

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.

See List

-	Recessive monogenic diseases	Dominant monogenic diseases	Polygenic diseases
Genetic causality	Strong	Intermediate	Weak
Penetrance	Full	Sometimes incomplete	Weak
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

Types

 chromosomal diseases by chromosomal anomalies
 genic diseases

• monogenic diseases (mendelian diseases)
• oligogenic diseases
• polygenic diseases (complex inheritance diseases, diseases with multifactorial inheritance)

Mechanisms

 chromosomal rearrangements (chromosomal diseases)
 genic mutations (genic diseases)

Monogenic 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

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.

Chromosomal diseases

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.

See also

 disease-related genes

References

 Ropers HH.New perspectives for the elucidation of genetic disorders.Am J Hum Genet. 2007 Aug;81(2):199-207. PMID: 17668371