ESPN 50th Annual Meeting

ESPN 2017


 
Genomic rearrangement events within Complement Factor H resulting in atypical Haemolytic Uraemic Syndrome
PATRICK WALSH 1 VALERIE WILSON 2 VICKY BROCKLEBANK 1 NEIL SHEERIN 1 SALLY JOHNSON 1 DAVID KAVANAGH 1

1- NATIONAL RENAL COMPLEMENT THERAPEUTIC CENTRE, UK
2- NORTHERN GENETIC SERVICE, NEWCASTLE UPON TYNE NHS FOUNDATION TRUST, UK
 
Introduction:

Atypical Haemolytic Uraemic syndrome (aHUS) is the triad of microangiopathic haemolytic anaemia thrombocytopenia and acute kidney injury. aHUS most commonly occurs due to inherited mutations in the alternative complement cascade, the most frequent mutations are in complement factor H (CFH). Mutations in CFH, resulting in aHUS, predominantly reside in the C-terminus, resulting in impaired surface binding. CFH, along with five highly homologous CFH related genes (CFHR1-5), is located within the Regulators of Complement Activation cluster. Due to the high degree of sequence homology, this region is prone to genomic rearrangement resulting in hybrid genes (CFH::CFHR1 and CFHR1::CFH). CFH::CFHR1 hybrids result in the exchange of the C-terminus of CFH with the C-terminus of CFHR1 (impairing surface binding), whilst CFHR1::CFH hybrids lead to replacement of the C-terminus of CFHR1 with the C-terminus of CFH (impairing complement regulation).

Material and methods:

All patients referred to the UK’s National aHUS centre with a diagnosis of aHUS (n=984) underwent Sanger sequencing of CFH to identify point mutations, and multi-ligation probe amplification (MLPA) to identify genomic rearrangement. Genomic rearrangement events generating CFH::CFHR1 hybrid were identified due to loss of CFH Ex.22/23 and gain of the corresponding region of CFHR1, Ex.5/6. CFHR1::CFH hybrids were identified due to loss of CFHR1 Ex.5/6 and gain of CFH Ex.22/23.

Results:

Sanger sequencing identified 86 patients with pathogenic variants in CFH. Analysis of the MLPA data revealed an additional 40 patients with either CFH::CFHR1 or CFHR1::CFH hybrids

Conclusions:

Genomic rearrangement of CFH is a common cause of aHUS. These events may not be identified by standard Sanger sequencing as the regions used to sequence are frequently involved in the rearrangement, resulting in alelle dropout. MLPA analysis can be used to identify genomic rearrangements, through addition or loss of CFH Ex.22/23 and CFHR1 Ex.5/6 sequence. This data highlights the need to perform MLPA analysis in patients with aHUS.