Xeroderma pigmentosum is an inherited Mendelian recessive disorder in
which the affected individuals are deficient in the repair of damaged
DNA. Since a major source of DNA damage results from the exposure of
skin to sunlight, the major symptoms of xeroderma pigmentosum are
pigment changes, keratoses, and ultimately, multiple skin cancers.
However, patients with xeroderma pigmentosum often have nervous system
damage as well. Xeroderma pigmentosum exists in at least nine distinct
forms; type A is both the most serious and the most common in Japan. In
a careful quantification of nerve damage in autopsy material from two
cases in Japan, investigators observed that although the motor nerves
were severely affected, the sensory nerves were even more severely
affected. The cause of this difference between the motor and sensory
nerves is not known, and the reason for the nerve damage in this disease
is not clear. The wide extent of the observed damage is consistent with
the prevailing notion that the nerve damage observed in type A xeroderma
pigmentosum is progressive. Ultraviolet light from the sun does not
reach the peripheral nerves as it does the skin, and careful avoidance
of sunlight has no effect on the development of the nerve damage.
However, the neurological damage revealed by the tabulation of changes
seen in these cases is similar to that observed in another disease,
ataxia telangiectasia. Since ataxia telangiectasia also involves
defective DNA repair, it seems reasonable to suggest that the observed
neuropathy in both diseases may be a direct result of this defect.
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