PF429 MOLECULAR GENETIC STUDY OF ACUTE INTERMITTENT PORPHYRIA IN RUSSIA
Authors: Goncharova M. , Pschenichnikova O. , Pustovoit Y. , Karpova I. , Surin V. 
Published: June 2019

Background:Acute intermittent porphyria (AIP) is one of the most common and severe form of porphyrias. It is an autosomal dominant inherited disorder caused by mutation in hydroxymethylbilane synthase gene (HMBS) with low penetrance, which does not exceed 10–20%. AIP acute attacks have highly variable predominantly neurological symptoms and the disease is often misdiagnosed. Therefore, a correct diagnosis is possible only using molecular genetic analysis.Aims:Our aims were to describe mutational spectrum of HMBS gene in Russian AIP patients and to determine and discuss the possible genetic reasons, which could determine the nature of AIP penetrance.Methods:We used samples of genomic DNA collected from unrelated AIP probands (N = 157) and their relatives (N = 308). We isolated nuclear DNA from peripheral white blood cells. Mutational analysis was performed using Sanger sequencing of all functionally important regions of HMBS gene. Besides, we performed Whole Exome Sequencing (WES) on a small group of AIP patients (N = 6) using TrueSeq Exome Library Prep kit (Illumina) and Illumina HiSeq4000 system. For bioinformatic analysis we used hg19 version of human genome as a reference and detected variants differing from it separately in each patient's DNA sample by GATK software. We chose for further analysis those variants, which were nonsynonymous substitutions, splicing, non‐frameshift insertions or deletions or were located in 5’UTR, and had no accession number in SNP databases.Results:We found 91 different mutations in HMBS gene in 157 unrelated AIP patients, 49 of them were not previously described. The most common HMBS gene defects in Russian AIP patients are c.53delT (N = 16) and Arg173Trp (N = 13). During patients’ families genetic consulting we also revealed 118 asymptomatic AIP carriers out of 308 relatives tested. Also, as a preliminary study of additional factors that could affect specific AIP penetrance, we performed WES. After WES data filtration, we revealed about 103–136 variations in each exome (118 in average), which could be considered as mutations. Spectra of mutated genes in different patients virtually did not overlap. This fact supports our hypothesis that AIP penetrance has oligo‐ or polygenic nature. In 5 out of 6 patients we found heterozygous mutations in several genes causing different neurodegenerative disorders, which have partly similar symptoms with AIP, e.g. congenital myastenic syndrome (CMS): AGRN (Val1200Ile), DOK7 (Arg47Cys), SCN4A (Leu96Phe), UNC13A (Arg459Gly), ALG8 (Tyr67Asn) and FBXO38 (Arg754His).Summary/Conclusion:We described mutational spectrum of HMBS gene in Russian AIP patients and revealed two major mutations, which need to be looked for in newly counseled patients in the first place. As a result of WES data analysis we propose a hypothesis about the influence of mutations in genes associated with neurodegenerative diseases on AIP penetrance. This hypothesis we are planning to examine on the expanded sample of AIP patients which suffered acute attacks and their asymptomatic carrier relatives.