As so-called "androgenic" tissues such as skin/hair follicles and male reproductive tissues are very high in 5α-reductase expression, while skeletal muscle is virtually devoid of 5α-reductase, this may primarily explain the high myotrophic–androgenic ratio and dissociation seen with nandrolone, as well as with various other AAS.Aside from 5α-reductase, aromatase may inactivate testosterone signaling in skeletal muscle and adipose tissue, so AAS that lack aromatase affinity, in addition to being free of the potential side effect of gynecomastia, might be expected to have a higher myotrophic–androgenic ratio in comparison. In addition, DHT is inactivated by high activity of 3α-HSD in skeletal muscle (and cardiac tissue), and AAS that lack affinity for 3α-HSD could similarly be expected to have a higher myotrophic–androgenic ratio (although perhaps also increased long-term cardiovascular risks). In accordance, DHT, mestanolone (17α-methyl-DHT), and mesterolone (1α-methyl-DHT) are all described as very poorly anabolic due to inactivation by 3α-HSD in skeletal muscle, whereas other DHT derivatives with other structural features like metenolone, oxandrolone, oxymetholone, drostanolone, and stanozolol are all poor substrates for 3α-HSD and are described as potent anabolics.The intracellular metabolism theory explains how and why remarkable dissociation between anabolic and androgenic effects might occur despite the fact that these effects are mediated through the same signaling receptor, and why this dissociation is invariably incomplete. In support of the model is the rare condition congenital 5α-reductase type 2 deficiency, in which the 5α-reductase type 2 enzyme is defective, production of DHT is impaired, and DHT levels are low while testosterone levels are normal.
Polyonychia also known as supernumerary nails is a condition in which two or more nails grow in the same finger or toe. Signs and symptoms
The signs/symptoms of polyonychia are very easy to detect: two or more nails growing on the same finger or toe. The nails can either be separate, small nails (micronychia) or one wide, almost complete nail, the digit affected could also be wider than normal

Causes
Polyonychia is generally caused by a congenital duplication of the distal phalange of the affected digit(s), this can be caused by congenital factors (sporadic without a genetic link) or by genetic factors (sporadic or familial with genetic link). It can also be caused by polysyndactyly, which is characterized as one normal digit being connected/webbed (syndactyly) to an extra digit (polydactyly). Polyonychia can also be acquired, such as after an accident that affected the nail bed causing it to split. This type of polyonychia is just referred to as "post-traumatic split nail" Polyonychias syndromic causes include:

Isolated congenital onychodysplasiaPolyonychias non-syndromic causes include:

Polyphalangism (more specifically of the distal phalange)
Polysyndactyly

See also
Polydactyly
Syndactyly
Polysyndactyly


== References ==