I had not heard of Alpha Mannosidosis before, so I looked it up. Both that and Developmental Duplication (DD) are recessive genetic conditions, meaning in order to be expressed, the animal must receive the gene from both their sire and Dam. There are tests that can be done to identify carriers of both. Zoetis is able to test for both. Neogen can do the DD test, but I don't know about the other. You will need to collect a blood or hair sample and send it into the lab. The test for DD is $22 through American Angus. 816-383-5100
DD was identified in a very popular Angus sire. Although it is a recessive it is not always expressed even when in the homozygous state. There are apparently other factors involved. Normally when two carriers of a recessive trait are mated to each other, ¼ of their offspring will express that trait. With DD that is not always true and there have been many animals identified as homozygous for DD who appear 100% normal. The defect, when expressed, often appears as an extra limb. If you have registered Angus cattle who have the potential for this defect, their pedigree will be marked DDP meaning Developmental Duplication Potential. Animals tested as carriers (meaning they carry a single gene) will be marked as "C" and those tested and found to be free of a defect will show "F". Never buy a registered bull marked as "P" or "C". Animals with no potential for an identified defect will not have a notation.
The Alpha Mannosidois defect was identified in Angus, Murray Grey and Galloway cattle in New Zealand. It apparently has also been found in North America, but I don't think it is very common here. I have not heard of it being identified in any registered American Angus cattle, but I suppose it is possible.