B-265 Prevalence of 844ins68 Polymorphism in the Cystathionine β-Synthase Gene in Brazilian Individuals
Authors: Rios J S , Silva J d , Malta F S , Zauli D A 
Published: September 2023

Abstract

Background
Deficiency of Cystathionine β-Synthase (CBS) is the most common cause of the homocysteine increase in blood and urine. This is an important autosomal recessive disorder with pleiotropic clinical manifestations in the vascular system, the skeletal structure, the ocular lens, and the central nervous system. Several polymorphisms in CBS gene have been associated with homocystinuria, with consequent premature arterial and/or venous occlusive diseases. The thymine-to-cytosine substitution at nucleotide 833 of the CBS gene (T833C) is the majority predominant mutation in individuals with homocystinuria. Several studies of T833C have been performed on patients where venous or arterial occlusive diseases are an important risk factor. The T833C causes a substitution of hydrophobic isoleucine by a more hydrophilic threonine at codon 278 (I278T) and affects the CBS conformation or the interaction of the CBS subunits. Most occurrences of T833C are known to segregate in cis with 844ins68 insertion polymorphism in the exon 8, duplicating the intron 7 splice acceptor. At the mRNA level, polymorphisms T833C and 844ins68 are skipped next to the use of this alternative splicing site. Therefore, previous studies about 844ins68 produced conflicting results that show a neutral or even effect protective of the insertion against occlusive venous and arterial occlusive disease. Thus, this study aims to describe the genotypic profile of the 844ins68 mutation in CBS gene in Brazilian individuals affect with vascular diseases or patients at risk for genetic variants segregating in the family.

Methods
The study group consisted of 1301 individuals submitted to the identification of the CBS 844ins68 in Grupo Pardini Laboratory. Genomic DNA was isolated from EDTA blood using QIAcard FTA Classic (Qiagen). To detect the insertion, the genomic fragments comprising the intron 7 and exon 8 in the coding region and splicing junctions of the CBS gene were amplified by Polymerase Chain Reaction (PCR).

Results
Our sampling included 214 men’s blood samples (16.4%) and 1087 women’s blood samples (83.5%). We found a prevalence of 21.6% individuals with the insertion. Males without the 844ins68 mutation (wild type) predominated 161/214, (75.2%), carriers of 844ins68 heterozygotes were 45/214 (21%), and homozygotes were 8/214 (3.7%). In female individuals, was found 859/1087 (79%) allele without 844ins68 (wild type), 214/1087 (19.7%) carriers of 844ins68 heterozygotes and 14/1087 (1.3%) homozygotes. The number of solicitations for the exam in women is greater compared to men.

Conclusions
Our findings show that the prevalence of 844ins68 in Brazil is compatible with others studies involving Brazilian women with cardiovascular defects. According to the literature, the insertion is most frequent in females than in males. Considering the possible restoration of non-mutated RNA through preferential splicing of the 844ins68, our study suggest that mutated individuals have the insertion as a protective factor for the development of venous or arterial occlusive diseases. The search of 844ins68 should be evaluated in association with the clinical aspects.