TISM

Toxically Induced Sexual Morphism is the central plot device of the Ridgewick Chronicles. A genetic disorder caused by environmental contaminants, TISM causes mutations in the Five-Alpha Reductase enzyme (5α-r), altering fetal DNA in utero. Higher levels of the toxin can cause death, still-birth and severe abnormalities; lower levels can lead to sterility, infertility and chimeras.

An extremely rare side effect of TISM is a form of pseudo-hermaphrodism in which the XY chromosome is "overwritten" by the endocrine system, giving the subject a hyper-feminized appearance. In extreme cases, the subject undergoes a complete anatomical metamorphosis, gradually transforming from male to female over a three year period.

Medical Variants
TISM is known to manifest in three primary forms:


 * Type One: Intersexual: patient is born with indeterminate sexual characteristics, sometimes with two sets of reproductive organs. Generally considered non-viable, though a small number (1.3 percent) are believed to be capable of conception following puberty.


 * Type Two: Pseudo-hermaphroditic: patient is born with visually female physical characteristics, which are retained throughout natural lifespan. Subject is usually non-viable, lacking any functional reproductive system.


 * Type Three: Transformative (informal: transfeminine): patient is born biologically male, frequently maintaining a sexually ambiguous appearance until the age of six or seven, when the subject undergoes a physical reconfiguration. Generally considered non-viable, though at least one documented case had displayed the potential for normal sexual reproduction.