RESUMEN
AIM: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.
Asunto(s)
Síndrome Hemolítico Urémico Atípico , Complemento C3/deficiencia , Factor I de Complemento , Enfermedades Genéticas Congénitas , Adulto , Síndrome Hemolítico Urémico Atípico/diagnóstico , Síndrome Hemolítico Urémico Atípico/epidemiología , Síndrome Hemolítico Urémico Atípico/genética , Niño , Preescolar , Estudios de Cohortes , Complemento C3/genética , Factor I de Complemento/análisis , Factor I de Complemento/genética , Femenino , Enfermedades Genéticas Congénitas/sangre , Enfermedades Genéticas Congénitas/epidemiología , Enfermedades Genéticas Congénitas/genética , Enfermedades por Deficiencia de Complemento Hereditario , Humanos , Lactante , Masculino , Mutación , Polimorfismo Genético , Túnez/epidemiologíaRESUMEN
Hereditary C1q deficiency (C1qD) is the most penetrant genetic factor predisposing to the development of lupus pathology with more than 93% of C1q deficient patients developing this autoimmune pathology throughout their life. It is a rare autosomal recessive deficiency, with only 67 cases reported so far including one Tunisian girl who died at the age of three from complications resulting from severe systemic lupus erythematosus. Although C1qD was confirmed in the serum of this patient using C1q ELISA and classical pathway specific functional assays, no DNA sample had been obtained from this patient. Here we report the analysis of sera and DNA of members of this patient's closer family. Our analysis identified a homozygous mutation within the gene encoding the C-chain of C1q leading to a deficiency of C1q in an older sister of our original patient. This mutation, termed g.5580G4C, represents a single basepair substitution in exon 1 of the C1q C chain gene which changes the codon of Gly61 to Arg 61. Amongst the other 14 mutations leading to C1qD, g.5580G4C represents the first reported transversion leading to human C1qD.