The New York Times featured an article on the high rates of "autism" among Somalis in Minnesota, but noted that it seemed different from the similarly high rates of autism among Minnesota whites because none of the Somali "autistics" had IQs over 70. 

In other words, it's not like Ludwig Wittgenstein or Glenn Gould-style autism, it's severe retardation. 

Retardation is also common among Pakistani immigrants in the English Midlands, due largely to high levels of cousin marriage. 

What about Somalis in Minnesota? From Wikipedia's article on "Cousin Marriage:"

A bill to repeal the ban on first-cousin marriage in Minnesota was introduced by Phyllis Kahn in 2003, but it died in committee. Republican Minority Leader Marty Seifert criticized the bill in response, saying it would "turn us into a cold Arkansas."[112] According to the University of Minnesota's The Wake, Kahn was aware the bill had little chance of passing but introduced it anyway to draw attention to the issue. She reportedly got the idea after learning that cousin marriage is an acceptable form of marriage among some cultural groups that have a strong presence in Minnesota, namely the Hmong and Somali.[113]

Somalia doesn't show up in A.H. Bittles' tables on Consang.Net, but here are some studies of cousin marriage in other cultures not hugely dissimilar:

Tanzania

37.8% first cousin marriages, Pangani - Household 503 Tanner (1958) (Muslims) survey 

Egypt

61.4% Nubia 1967/68 Household 611 D1C,1C,1 1/2C,2C  Badr (1972) (Fadetchi) survey

62.0% Nubia 1967/68 Household 757  D1C,1C,11/2C,2C Badr (1972) (Kenuzi) survey 

69.8% Nubia 1967/68 Household 414 69.8 D1C,1C,11/2 C,2C Badr (1972) 

(Arabs) survey 

63.6% All-Nubia 1967/68 Household 1,782 63.6 D1C,1C,11/2 C,2C Badr (1972) 

Sudan

44.2% Gezira 1969/74 Household 2,999 44.2 1C 0.0028 Ahmed (1979) survey 

18.3% Khartoum - Blood donors 345 18.3 1C,2C Saha & El Sheikh (Nilotes) (1988) 

 45.7% Khartoum - Blood donors 302 45.7 1C,2C Saha & El Sheikh (Negroids) (1988) 

55.2% Khartoum - Blood donors 4,186 55.2 1C,2C  Saha & El Sheikh (Arabs) (1988) 

52.0% All- - Blood donors 4,833 52.0 1C,2C Saha & El Sheikh Khartoum (1988)

Burkina Faso

65.8%  North - Household 308 65.8 1C,2C Hampshire & (Fulani) survey Smith (2001)