Identification of two novel variants, c.-35A>T and c.[-35A>T, 725T>G], in the FUT1 gene in a patient exhibiting the para-Bombay phenotype.

Background: Reduced or absent H antigens on red cells with the (para-)Bombay phenotype can arise from FUT1 gene mutations, impacting the structure and function of 1,2-L-fucosyltransferase 1 (1,2-L-FucT1). Here, we identified the novel mutations in one patient displaying the para-Bombay phenotype and examined the potential molecular mechanisms underlying this phenotype.

Materials and methods: ABH antigens and antibodies were detected in patient's blood and saliva using serological methods. The genotypes of ABO, FUT1, and FUT2 were imputed using the genetic variations discovered in the whole exome sequencing data. Three-dimensional (3D) models of FUT1 variants were built using Deepmind's AlphaFold2 and HDOCK, and the possible effects of the variants were predicted to evaluate using DynaMut2 and Polyphen-2.

Results: Serological analysis confirmed the para-Bombay B phenotype producing anti-HI and exhibiting normal genotypes ABO*B.01/O.01.02 and FUT2*01.09/01.09. Remarkably, the phenotype is caused by a compound heterozygous genotype: one allele containing the novel c.-35A>T mutation and the known c.725T>G mutation (p.Leu242Arg) of FUT1, and the other allele containing the c.-35A>T mutation. From the computerized stimulation analysis, p.Arg242 of the FUT1 variant may be detrimental, destabilizing, and probably damaging to 1,2-L-FucT1, although not altering the 3D structure of the entire enzyme. The c.-35A>T promoter DNA left at the binding interface of both ZID and c-Rel transcription factors may enable regulation of 1,2-L-FucT1 function at gene promoters.

Conclusion: We identified the two novel variants, c.-35A>T and c.[-35A>T, 725T>G], in the FUT1 causing the para-Bombay phenotype. This finding may clarify the molecular mechanisms and enhance blood transfusion safety.