Inheritance Patterns Of Monogenic Traits

The analysis of inheritance patterns is a key element in the investigation of singlegene pharmacogenetic traits. Despite the addition of important new genomics tools arising from the human genome initiative, many years will pass before we completely understand the role of specific genetic factors and their interactions with environmental factors in health and disease. Until that time, it will be most effective to integrate genotypic data with data gained from the family history to profile individual drug responses and to individualize medical care. The availability of computer-based tools promises to reduce the time needed to obtain, organize, and analyze family history information, and provide a more lasting reminder of the value of this information and a way of keeping it up to date.27

This technique involves the collection of data on the family history and transmission patterns of the trait from parents to offspring. Information sought includes the age, sex, health status, and occupations of the parents, siblings, and other close relatives. The exact relationship of the index case (the case that brings the family to the investigator's attention) to the relatives and the occurrence of consanguineous matings, miscarriages, stillbirths, and twinships may provide useful information. Information about the ethnogeographic origin of the parents is important, and a detailed inquiry about the therapeutic agents and environmental exposures that may have occurred in the workplace or elsewhere is also important.

Four inheritance patterns are commonly observed within human families: autosomal dominant inheritance, autosomal recessive inheritance, sex (X)-linked dominant inheritance, and sex (X)-linked recessive inheritance. Another familial pattern attributable to mitochondrial inheritance has been observed, but much less frequently. Pedigrees are charted to show the relationships between the index case and other relatives in the family tree. Symbols commonly used to chart pedigrees are defined in Figure 5.1.

I I Parents with children

LJ O (in order of birth)

Mating

Consanguineous Mating

Male

Female

Sex Unspecifie

Dizygotic Twins Monozygotic Twins

Zygosity uncertain

Female with children by two males

Couple Infertile

0 Homozygous a ยป

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