Molecular genetic analysis for the B(3) allele.

Area of Science:

• Molecular Genetics
• Blood Group Serology
• Human Genetics

Background:

• The B(3) phenotype is a rare blood group variant.
• Understanding the molecular basis of blood group phenotypes is crucial for transfusion medicine and population genetics.
• Previous studies have identified various genetic alterations associated with weak B phenotypes.

Purpose of the Study:

• To investigate the molecular genetic basis of the B(3) phenotype in 14 unrelated individuals.
• To identify specific mutations in the blood group B gene responsible for the B(3) phenotype.
• To elucidate the functional consequences of these mutations on gene expression and protein product.

Main Methods:

• Molecular genetic analysis of the blood group B gene.
• DNA sequencing to identify mutations.
• Reverse transcription polymerase chain reaction (RT-PCR) to analyze messenger RNA (mRNA) transcripts.
• Analysis of splice donor sites and exon skipping.

Main Results:

• Two distinct molecular changes were identified in the blood group B gene.
• One individual had a 247G --> T mutation predicting an Asp83Tyr alteration.
• Thirteen individuals had an IVS3 + 5G --> A mutation in intron 3.
• The IVS3 + 5G --> A mutation disrupted the splice donor site, leading to exon 3 skipping during mRNA processing.
• The resulting B(3) transcript lacked exon 3, predicting a B-transferase product deficient in 19 N-terminal amino acids.

Conclusions:

• The IVS3 + 5G --> A mutation is a significant cause of the B(3) phenotype, leading to aberrant mRNA splicing.
• Exon skipping due to splice site mutations can result in functionally altered blood group antigens.
• These findings contribute to the understanding of genetic heterogeneity in blood group B variations.