Analysis of the family tree (genealogy)
Every known member of the patient’s family is drawn into the family tree (genealogy).
Preparation for a genealogic study may be a reason for family visits and for investigations of older medical records.
If a hereditary condition affects some of the family members and if the data concerning the affected relatives are available and trustworthy, it is possible to determine the type of hereditary transmission and the risk for other family members.
If the inheritance of the disease does not correspond to the situation in the genealogy, it is a reason to dispute the "official" diagnosis. The genealogic analysis and determination of the type of inheritance for an uncertain disease may contribute to its recognition. All the known diseases and defects of fertility of the family members are considered.
Blood relationship rate is assessed in case of blood relations.
The analysis of symptoms and fate of the affected relative may have various consequences on the patient: it may be completely unacceptable for him/her or, on the contrary, absolutely insignificant.
Genetic diseases are divided into four groups:
- diseases with the Mendelian type of inheritance. The cause is a change (mutation) of a separate gene with clear regular transfers into the following generations. The name comes from an Austrian-Hungarian monk Gregor Mendel, who defined the principal patterns of inheritance in Brno in 1868.
- chromosomal disorders. The cause is a mutation of such large blocks of genes (chromosomes) that it can be observed using a microscope. Mostly they originate incidentally from a damaged genital cell (ova, or less often the sperms).
- multifactorial diseases. These originate due to the effects of external environment on several genes of low impact. They may be manifested at birth (e.g., cleft palate) or at later stages of life (e.g., increased blood pressure).
- diseases due to somatic mutations. They originate due to cascade mutations of more genes in certain cells during the course of life. Such mutated cell may form the basis of a tumour.