Using ddPCR to Identify Large Deletions of Complement Factor H-Related Genes in Atypical Hemolytic Uremic Syndrome
Yu-Wei Cheng1,2, Zhen Wang3, Zheng Jin Tu1
1Department of Laboratory Medicine, Cleveland Clinic, Cleveland, OH, United States.
Background:
Atypical hemolytic uremic syndrome (aHUS) is a rare, complement-mediated disorder. Disease-associated variants have been found in complement factor H-related genes and complement regulatory genes. Particularly, homozygous deletions of CFHR1, CFHR3, or CFHR4 have been associated with aHUS. Generally, multiplex ligation-dependent probe amplification (MLPA) is used to detect copy number changes in the CFH and CFHR regions. We have developed a cost-effective droplet digital PCR (ddPCR) method for measuring copy number variations (CNVs) in these genes.
Methods:
A total of 41 DNA samples were analyzed using both ddPCR and MLPA to assess large deletions in the CFHR1, CFHR3, CFHR4 regions. The ddPCR primers were designed to avoid rare single nucleotide polymorphisms to enhance hybridization efficiency and accurate identification of deletions within the CFHR regions. The MLPA probe mix (Probemix P236 CFH Region) targeting CFHR regions was purchased from MRC Holland.
Results:
Multiple heterozygous deletions were observed in the CFHR1, CFHR3, and CFHR4 genes. Homozygous deletions of CFHR1 and CFHR3 were seen in 2 cases, while 2 other cases showed homozygous CFHR1 and heterozygous CFHR3 deletions. All 41 samples demonstrated 100% concordance in copy number results between ddPCR and MLPA, as well as consistent reproducibility in both inter- and intratechnologist evaluations.
Conclusions:
Our findings demonstrate that ddPCR is a robust platform to identify large deletions in the CFHR regions. Future studies are needed to evaluate its ability to distinguish full vs partial deletions and to further establish its clinical diagnostic value.
