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Fumarase deficiency is an autosomal recessive disorder, and it is necessary for the individual to receive the mutation from both parents. It can't be contracted like that. However i would request you to send me some pictures of his tumors if you have any, for us to get a clearer picture. Also are there any reports mentioning that he has Fumarase enzyme deficiency? Does he have any other problems?
Fumarase deficiency can lead to a lot of symptoms,but mostly neurological. Normally people also present with severe mental retardation. Did your husband ever have any neurological symptoms?

If possible send me a few images and we can go ahead with the consult.

Thanks,

Doctor Spring