Penetrance, genetic

Penetrance Genetic term referring to the degree to which an inherited characteristic is expressed. 

The viruses responsible for AIDS are human immunodeficiency virus 1 and 2 (HIV 1 and HIV 2) Both are retroviruses, meaning that their genetic material is RNA rather than DNA HI Vs require a host cell to reproduce and the hosts m humans are the T4 lymphocytes which are the cells primarily responsible for inducing the immune system to respond when provoked The HIV penetrates the cell wall of a T4 lymphocyte and deposits both its RNA and an enzyme called reverse transcriptase inside There the reverse transcriptase catalyzes the formation of a DNA strand that is complementary to the viral RNA The transcribed DNA then serves as the template from which the host lymphocyte produces copies of the virus which then leave the host to infect other T4 cells In the course of HIV reproduction the ability of the T4 lymphocyte to reproduce Itself IS compromised As the number of T4 cells decrease so does the body s ability to combat infections... 

Genetic transmission in nemaline myopathy is the subject of some uncertainty. A Japanese study of 50 pedigrees came to the conclusion that autosomal dominant with reduced penetrance was the most probable mode. However a Finnish study presented evidence for autosomal recessive transmission. There is no evidence that severe and mild forms are genetically distinct and several pedigrees contain members showing widely differing clinical severity. A candidate gene for autosomal dominant nemaline myopathy has been localized to chromosome Iq 21—23. 

The genetic trait for MH is not sex-linked and both men and women can inherit MH. Inheritance in humans appears to be autosomal dominant with variable penetrance. Studies of large families have documented an autosomal dominant pattern. McPherson and Taylor (1982) studied 93 families in whom MH occurred. Even though various patterns of inheritance did emerge in the study we should assume that 50% of children are at risk in MH susceptible families. Kalow and Britt (1992) suggested that, in some families, at least two different non-allelic genes are likely to be present, one of which is probably autosomal dominant but rare, and the other autosomal recessive but common. 

Laubichler, M. and Sarkar, S. (2002), Flies, genes, and brains Oskar Vogt, Nikolai Timofeeff-Ressovsky, and the origin of the concepts of penetrance and expressivity , in L. S. Parker, and R. Ankeny (Eds), Medical Genetics, Conceptual Foundations and Classic Questions, Kluwer, Dordrecht, The Netherlands, in press. 

Only 2% of total plasma testosterone is present in the active unbound state that penetrates the prostate cell, where it is converted to DHT by 5 a-reductase. DHT subsequently binds with a cytoplasmic receptor and is transported to the cell nucleus where transcription and translation of stored genetic material occur. 

These genetic maps have been the backbone for the highly successful endeavors of the molecular genetics community to identify highly penetrant... 

Several classic pharmacogenetic traits are listed in Table 8.1 and discussed below. For a variety of reasons, mostly reflecting the slow penetration of genetic thinking into clinical medicine and the limited predictive value of even the best-validated tests, these tests have been significantly underutilized. 

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