No evidence for a large difference in ALS frequency in populations of African and European origin: a population based study in inner city London. - Rojas-Garcia R; Scott KM; Roche JC; Scotton W; Martin N; Janssen A; Goldstein LH; Leigh PN; Ellis CM; Shaw CE; Al-Chalabi A (Amyotrophic lateral sclerosis : official publication of the World Federation of Neurology Research Group on Motor Neuron Diseases, 2012)