Molecular basis of complement factor I deficiency in Tunisian atypical haemolytic and uraemic syndrome patients

The aim of the present study was to characterize the molecular basis of complement factor I deficiency in Tunisian atypical haemolytic and uremic syndrome patients with low factor I levels.

Six adults and seven children were enrolled in this study. Complement factor I levels were assessed by a homemade sandwich ELISA and ranged between 12.5% and 60%. Genomic DNA was amplified by way of a polymerase chain reaction using intronic primers flanking the 13 coding exons. Sequencing of amplified products was carried out by the dye terminator sequencing method. Molecular study was performed on parental samples for three dead paediatric patients. The control group consisted of 100 healthy Tunisian donors.

We identified a total of 13 substitutions and one insertion: seven in introns, four in exons and three in UTR. The new mutations were c.-132G > C, c.71 + 181 T > A in 5'UTR and intron 1, respectively. Three intronic polymorphisms were predicted to have impact on splicing events: c.482 + 6C > T, c.884-42_884-41insTTAAA (rs34422850) and c.1429 + 33 A > G (rs9998151). They were three missense mutations leading to a p.Ile 357Met, p.Ile416Leu and p.GLu548Gln. p.Ile 357Met was found in two patients and one relative. Half of the patients had associated mutation and/or polymorphisms.

This is the first genetic study in Tunisian and Maghrebin atypical haemolytic and uraemic syndrome patients. The high occurrence of Ile357Met mutation may reflect a founding effect. Functional impact of the two new mutations c.-132G > C and c.71 + 181A > T have to be studied. Association of simultaneous genetic abnormalities may explain the variability of atypical haemolytic and uraemic syndrome, penetrance and disease phenotype.