Control treatment

In order to make sure that the "wolf syndrome" is caused by the deletion of these genes, you must test a "control group". The control, should be people that without the certain syndrome. So, if the deletion is not present in these people, you may assume that the wolf syndrome is probably caused by the deletion of these 4 genes.

In our case, (and in my opinion) the most suitable controls would be members of these three families without the syndrome.
This is better than taking random people without the syndrome, because:
The deleted genes might be a inherited characteristic, only present in that certain family, that isn't directly related with wolf syndrome.

In that case, if you search random people, you may not find anyone with the same deletion, and you might wrongly conclude that the wolf syndrome is the result of the deletion of these genes.

On the other hand, if you search members of these 3 families, you can determine more precisely whether the gene deletion has something to do with wolf syndrome:
Let's assume you search several non-syndrome family members.
1)If no one of them has the gene deletion, then probably the syndrome and the deletion are directly related. That is because otherwise it would be quite unlikely that only the wolf-syndrome people are inheriting the deletion.
2)If some of them had the same deleted genes, then you conclude that these is some connection between the deleted genes and the syndrome (since all the people with the syndrome have the deletion), but there are other factors that determines whether the person will have the syndrome or not (since not all people with the deleted genes has the syndrome).
3)If all of them had the same deleted genes as well, then you conclude that the relation between syndrome and gene deletion is non exsistant, and the deleted genes is a characteristic of the family. (this 3rd case is not very likely to happen, because it requires that ALL the members of these families has the same non-common genetic characteristic. Your results will probably be the 1st or the 2nd case.)