A Lys256Glu mutation, such as is associated with familial focal and segmental glomerulosclerosis (FSGS) was introduced into exon 8. In addition, a loxP flanked neomycin-resistance cassette was inserted 400 base pairs 3' of exon 8. The neomycin resistance cassette was removed by mating mice with Tg(Prm-cre)58Og, resulting in transcript expression that is similar to the expression in wild-type, as indicated by Northern blot. RT-PCR and sequencing of exon 8 confirmed that the transcript contains the point mutation, K228E.