The present invention relates to a Crumbs homologue (CRB) therapeutic for use as a medicament or in a method of treatment or prophylaxis for example in the treatment or prophylaxis of a retinal disorder due to mutations in the Crumbs homologue 1 (CRB1)gene such as Leber s congenital amaurosis 8(LCA8) or retinitis pigmentosa 12 (RP12).In particular the present invention relates to a recombinant viral vector comprising CRB2 or modified non toxic forms of either CRB1or CRB3 that resemble CRB2.