In order to assess how likely it is to find a disease-causing mutation in outbred single affecteds with mutations in a recessive disease gene using the approach described here, we prospectively performed 250 k SNP DNA microarray analysis in 24 unrelated outbred patients with infantile nephrotic syndrome, which is known to be caused by NPHS1 mutations in 22.5% of cases (18/80) [3] and by PLCE1 mutations in 28% of cases (10/35) [24]. The gene discussed is PLCE1; the disease is nephrotic syndrome.