Experimental
cyanide exposure in animals causes
demyelination and circumstantial clinical and laboratory evidence suggest that there are human parallels. In
Leber's hereditary optic atrophy there appears to be a defect in the conversion of
cyanide to
thiocyanate because of deficient
rhodanese activity. For transmitters of the disease smoking carries the risk of
blindness and in the most severely affected patients, there is diffuse neurological disease. It is possible that other
hereditary optic atrophies (dominant and recessive) may also reflect inborn errors of
cyanide metabolism. In the
retrobulbar neuritis and
optic atrophy of
vitamin B12 deficiency there may be a conditional abnormality of
cyanide metabolism in smokers, and likewise in so-called tobacco-alcohol
amblyopia in which there are more complex
nutritional deficiencies. Epidemiological evidence (differing sex ratios, excess of smokers) indicates that defective
cyanide metabolism may contribute to the development of sub-acute combined degeneration of the cord in
vitamin B12 deficiency. In
protein-malnourished populations consuming large amounts of
cyanide or cyanogens, viz. in tropical Africa where the staple diet includes cassava containing large amounts of
linamarin, similar maladies occur as acquired disorders. There may be a similar explanation for
lathyrism. The known pathways of human
cyanide metabolism are reviewed and evidence supporting the clinical data is presented.