Diseases: Sex Linked and Sex Influenced


by Richard Nixon
Honors Biology
Mrs. Linda
December 19, 1994

There are thousands of cases of sex linked and sex influenced diseases
worldwide. These diseases can range from a social inconvenience, to a fatal
ailment. In sex linked diseases, like Muscular Dystrophy, hemophilia and color
blindness, only males are affected. When a man infected with a sex linked
disease has children, all his sons are normal, but all of his daughters are
carriers. When a carrier woman and an uninfected man have children, half of the
sons are normal, and half of the sons are affected; half of the daughters are
carriers and half of the daughters are normal. Only males are affected because
the sex linked diseases affect the X chromosome. Males have one X chromosome
and one Y chromosome, so they need to use that X, whether it is flawed or not.
Females on the other hand, have two X chromosomes, so if one is defective, they
can use their second X chromosome. Duchenne\'s Muscular Dystrophy(DMD) is
defined as "a genetic disease characterized by defective muscle cells that can
not produce a protein called dystrophins (Science News 380). In patients of
hemophilia, there is a deficiency of a protein needed for blood clotting,
causing this hereditary bleeding disorder. In red/green color blindness, the
broadest form of color blindness that affects six percent of the population, the
cones in the retina that receive green light do not function properly. Unlike
sex linked diseases, sex influenced diseases are not reserved solely for the
male. However, the diseases occur in males much more frequently than in females.
This is because sex influenced diseases occur from imbalances in testosterone,
much more highly concentrated in males. Baldness and gout are two diseases that
are a result of these hormonal imbalances. Baldness is defined as the lack or
loss of hair. Permanent baldness strikes on a hereditary basis because the
hormonal imbalances tend to be passed from generation to generation. Gout is a
hereditary metabolic disorder that involves recurrent acute attacks of severe
inflamm ation of joints.
Sex linked diseases are born when sex genes, that compose two of the 46
chromosomes, are mutated by an error in copying genes in reproduction. One of
these sex linked diseases is Duchenne\'s Muscular Dystrophy. DMD is a disease
that has rightfully been gaining some headlines recently, as the disease is
taking the lives of young children. Several cures have been brought up recently
in the medical society, but none have paid any dividends. According to the
Muscular Dystrophy Association, one in every 2500 boys are infected with
muscular dystrophy. The defective gene is found at the top of the X chromosome.
This gene is the largest known to exist. In patients of DMD, this gene is
either missing or severely mutilated. The symptoms of DMD are fatal. By age
eleven, the victims weaken fast. Normally, muscle deterioration begins in the
lower legs and then moves up the body of the patient. Generally, victims are in
their early twenties when they die from either heart failure or diaphragm
failure.(The diaphragm is the muscle that makes breathing possible.) One mother
of a Duchenne\'s Muscular Dystrophy patient says succinctly, "Eventually these
kids get bedridden and then they die."(Grady 87) It is imperative to find a
cure for Duchenne\'s Muscular Dystrophy so we can save the lives of thousands of
innocent children.
One of the major researchers working on a cure for DMD is Dr. Peter K. Law
of the Cell Therapy Research Foundation. Law has been in the field for over
twenty years and has made many discoveries. In 1972, Law\'s doctoral thesis
proved that dystrophic muscle cells have abnormal cell membranes. This showed
that the disease was caused by a muscle defect, not a nerve defect as was
previously thought. Since it was clear that it was a muscle defect, Law tried
to transplant both whole and minced muscle into mice. The minced muscle proved
to be too damaged to operate, and the whole muscle was so large that it died
before an adequate blood and nerve supply was developed. At this point, since
the whole muscle was too large but was the only feasible solution, he decided to
transplant whole muscles of a baby mouse into an adult mouse. This muscle was
not damaged, because it was not minced, and it was not too large, because the
baby muscle is considerably smaller than an adult muscle. Not only did the
mouse survive, but normal function was restored to diseased adult muscle. Since
the transplantation of muscle in mice was so successful, Dr.