Analysis of SERPING1 expression on hereditary angioedema patients: quantitative analysis of full-length and exon 3 splicing variants.

Hereditary angioedema (HAE) due to C1-inhibitor (C1-Inh) deficiency is an autosomal dominant disease caused by mutations in the SERPING1 locus. According to protein levels in plasma, two HAE phenotypes have been described: Type I, with low circulating protein levels in plasma, and Type II, where the protein is present but dysfunctional. Although more than 200 mutations have been described to date, studies on the molecular basis of this autosomic dominant trait are scarce. Previous studies demonstrated that C1-Inh mRNA expression was decreased in HAE patients. Herein, we have confirmed these findings in a large series of Spanish patients. Moreover, when our data were analyzed taking into account the type of mutation carried by the patient (i.e., missense, frameshift,…), significant differences were amongst the control, nonsense and splicing mutations groups (P<0.05). By opposite, no differences in C1-Inh mRNA expression were found between the control and HAE Type II groups, nor between treated and untreated patients groups, although a significant difference was observed between controls and untreated HAE Type I patients. An alternative splicing event has been described in the SERPING1 locus resulting in two different transcripts: the full-length and a shorter variant with skipping of exon 3. In order to investigate a possible role for this splicing in HAE, we quantified both mRNA variants in a series of 28 patients. No statistical differences were found in the expression of both variants between controls and patients when compared. However, a separate analysis considering each type of mutation evidenced a significant decrease (P: 0.0156) in the expression of the exon 3 skipping variant in those HAE Type I patients carrying nonsense mutations. Besides, median of the full variant's copy number was statistically decreased on the splicing group when compared with either stop and/or missense groups. The results of these studies provide new data about C1 inhibitor expression in HAE patients and shed more light on the transcriptional regulation of the SERPING1 locus. Quantitative analysis of splicing variants could help to determine the eventual variations of these two transcripts and their possible role under inflammatory stimuli.

Molecular characterization of three new mutations causing C5 deficiency in two non-related families.

Deficiencies in complement components are rare diseases whose diagnosis is often underestimated. In addition, in only a few cases molecular studies have been carried out for the characterization of the underlying genetic defects. To date, studies involving C5-deficient patients are scarce. The aim of the present report is to characterize the biochemical and molecular complement deficiency in two non-related families with one or more members showing no detectable hemolytic complement activity (CH50<50 U/ml) and reporting a history of several episodes of meningitis. Protein deficiency was assessed by means of hemolytic assays, bi-dimensional double immunodiffusion, ELISA and Western blot of patients' sera. Molecular studies were carried out by PCR and RT-PCR of DNA and RNA, respectively, both extracted from fresh blood samples of each family member. In Family A, only the propositus had complete C5 deficiency. Molecular studies showed that he was heterozygous for two changes in the C5 gene. One of the mutations was also carried by the father (c.1883_1884AGC, Y846H) was a de novo mutation. In Family B, the two C5-deficient members share the homozygous nonsense mutation c.892C>T (Q298X) in exon 9. The characterization of these new mutations is interesting in order to elucidate structure-function relationships in the C5 gene and it also helps to understand the molecular basis of this uncommon deficiency. Moreover, this report highlights the importance of complement screening in cases of repeated meningococcal infections in order to establish its involvement and to consider adequate clinical recommendations such as prophylactic antibiotics or meningococcal vaccines.