Genetic studies have shown that mutations of complement inhibitors such as membrane cofactor protein, Factors H, I, or B and C3 predispose patients to atypical hemolytic uremic syndrome (aHUS). Factor I is a circulating serine protease that inhibits complement by degrading C3b and up to now only a few mutations in the CFI gene have been characterized. In a large cohort of 202 patients with aHUS, we identified 23 patients carrying exonic mutations in CFI. Their overall clinical outcome was unfavorable, as half died or developed end-stage renal disease after their first syndrome episode. Eight patients with CFI mutations carried at least one additional known genetic risk factor for aHUS, such as a mutation in MCP, CFH, C3 or CFB; a compound heterozygous second mutation in CFI; or mutations in both the MCP and CFH genes. Five patients exhibited homozygous deletion of the Factor H-related protein 1 (CFHR-1) gene. Ten patients with aHUS had one mutation in their CFI gene (Factor I-aHUS), resulting in a quantitative or functional Factor I deficiency. Patients with a complete deletion of the CFHR-1 gene had a significantly higher risk of a bad prognosis compared with those with one Factor I mutation as their unique vulnerability feature. Our results emphasize the necessity of genetic screening for all susceptibility factors in patients with aHUS.

Background and purpose:  For many years, it was suspected that sheep expressed only one melatonin receptor (closely resembling MT₁ from other mammal species). Here we report the cloning of another melatonin receptor, MT₂, from sheep.Experimental approach:  Using a thermo‐resistant reverse transcriptase and polymerase chain reaction primer set homologous to the bovine MT₂ mRNA sequence, we have cloned and characterized MT₂ receptors from sheep retina.Key results:  The ovine MT₂ receptor presents 96%, 72% and 67% identity with cattle, human and rat respectively. This MT₂ receptor stably expressed in CHO‐K1 cells showed high‐affinity 2[¹²⁵I]‐iodomelatonin binding (K_D= 0.04 nM). The rank order of inhibition of 2[¹²⁵I]‐iodomelatonin binding by melatonin, 4‐phenyl‐2‐propionamidotetralin and luzindole was similar to that exhibited by MT₂ receptors of other species (melatonin > 4‐phenyl‐2‐propionamidotetralin > luzindole). However, its pharmacological profile was closer to that of rat, rather than human MT₂ receptors. Functionally, the ovine MT₂ receptors were coupled to G_i proteins leading to inhibition of adenylyl cyclase, as the other melatonin receptors. In sheep brain, MT₂ mRNA was expressed in pars tuberalis, choroid plexus and retina, and moderately in mammillary bodies. Real‐time polymerase chain reaction showed that in sheep pars tuberalis, premammillary hypothalamus and mammillary bodies, the temporal pattern of expression of MT₁ and MT₂ mRNA was not parallel in the three tissues.Conclusion and implications:  Co‐expression of MT₁ and MT₂ receptors in all analysed sheep brain tissues suggests that MT₂ receptors may participate in melatonin regulation of seasonal anovulatory activity in ewes by modulating MT₁ receptor action.

The existence of interindividual variations in G protein-coupled receptor sequences has been recognized early on. Recent advances in large-scale exon sequencing techniques are expected to dramatically increase the number of variants identified in G protein-coupled receptors, giving rise to new challenges regarding their functional characterization. The current minireview will illustrate these challenges based on the MTNR1B gene, which encodes the melatonin MT2 receptor, for which exon sequencing revealed 40 rare nonsynonymous variants in the general population and in type 2 diabetes (T2D) cohorts. Functional characterization of these MT2 mutants revealed 14 mutants with loss of Gi protein activation that associate with increased risk of T2D development. This repertoire of disease-associated mutants is a rich source for structure-activity studies and will help to define the still poorly understood role of melatonin in glucose homeostasis and T2D development in humans. Defining the functional defects in carriers of rare MT2 mutations will help to provide personalized therapies to these patients in the future.