VISA DENIED...PLZ HELP!!

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One of my friend had sponsored her husband for K3 visa. She's a US citizen and he's living in Pakistan. They rejected his visa and the basis of rejecting the visa is quite strange. See, according to Pakistani culture and religion it's permissible and quite normal for first cousins to get married. They are both first cousins from both maternal and paternal side. Now, after the interview the US immigration asked them to take a DNA test to prove they are not real brothers and sisters. The test came out as 15% or so of blood relation which they thought was fine and he was asked to come to the consulate again a few weeks after they received the DNA samples and when he went there they rejected his visa because they feel that they are related but not married. Now how should they go about appealing for this case? Does she write a letter to the congressman of her area? And if yes, then how should they go about doing that? She's very upset and any help in this regard would be appreciated.