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Includes assay photos showing the distribution of 5AR enzymes in various organs.


Tissue Distribution and Ontogeny of Steroid 5a-Reductase Isozyme Expression

http://www.pubmedcentral.nih.gov/picren ... obtype=pdf

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Interesting bit, that 5AR1 (found predominently in liver and skin) can compensate for 5AR2 in 5AR2-deficient individuals, enabling them to virilize at puberty and have normal DHT levels -- despite not having 5AR2 enzyme:



An intriguing feature of5a-reductase type 2 deficiency has
been the observation that affected individuals virilize to different
extents during puberty (3-5). Masculinization occurs regardless
of the type of mutation present in the SRD5A2 gene,
i.e., both in subjects with a complete deletion of the gene, and
hence no residual type 2 activity, and in subjects with only
qualitative defects in the enzyme (16, 18).

Two findings reported
here are consistent with a role for the5a-reductase type
1 isozyme in the observed virilization. First, the expression of
this isozyme begins at or near birth in the liver and continues
throughout life in this organ (Fig. 6). Second, the synthesis of
the type 1 isozyme is induced at or during puberty in the skin
and scalp and continues thereafter (Figs. 6, 8, 9).

Given the
large contribution of the skin and liver to relative body mass
(- 25%), it is reasonable to assume that the production of
dihydrotestosterone by these organs at puberty drives virilization
of the external genitalia and influences the pattern of hair
distribution in type 2-deficient subjects.

If this hypothesis is
correct, then dihydrotestosterone can act in a true endocrine
fashion as well as by the autocrine or paracrine mechanisms
typically ascribed to this hormone (3).

Two clinical observations
support this hypothesis. First, individuals with a complete
deletion of the type 2 gene (12) can have serum dihydrotestosterone
levels within the normal range (5).

Second, the administration
of testosterone to an individual with a splicing mutation
in the type 2 gene results in normal serum dihydrotestosterone
levels (31 ).