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singular condition of risk is an Rh+ father, an Rh- mother, and an Rh+ fetus. Exchange of blood during or at the end
of pregnancy can result in antibodies being formed by the mother to the Rh+ red blood cells of the fetus. This can
cause death of a subsequent Rh+ fetus, if not treated. This problem is now treatable by a manufactured gamma
globulin (RHOGAM) which removes the Rh antibodies from the mother's blood stream. Incidentally, while long
believed to be a standard two allele system with complete dominance (Rh+ > Rh-), it is now apparent that the Rh
blood group is more complex, but it is not clear if it consists of a single gene with multiple alleles or a group of very
closely linked genes that together determine Rh blood type.
***Galactosemia (230400): An enzyme deficiency disease preventing the utilization of lactose (milk sugar). The
sugar galactose accumulates in the brain causing severe mental retardation and early death if not treated. The
condition is readily detectable at birth and is treated via a lactose-free diet. Frequency = 1/200,000 live births.
***Hemochromatosis (235200 and others): The most common genetic disorder in America with a homozygous
frequency of 1/300 in Caucasians; caused by an enzyme deficiency. There is still debate as to whether this is a
recessive, dominant, or partially dominant trait, and it is likely that the genetics are complicated by the prevalence of
different mutations with different properties in the population and the fact that females seem to have a lower risk for
disease. Hemochromatosis is caused by mutations to the gene for the HFE protein, which regulates iron uptake, and
results in iron overload because of enhanced absorption of dietary iron. Severe clinical consequences include liver
cancer (14% incidence) and other common diseases that result in shortened and lower quality of...
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