Antioxidant enzymes, presbycusis, and ethnic variability

Area of Science:

• Genetics
• Otolaryngology
• Biochemistry

Background:

• Oxidative stress in the cochlea is a proposed mechanism for presbycusis (age-related hearing loss).
• Glutathione S-transferase (GST) and N-acetyltransferase (NAT) are key antioxidant enzymes found in the cochlea.

Purpose of the Study:

• To investigate the association between polymorphisms in GSTM1, GSTT1, and NAT2 genes and presbycusis.
• To determine if ethnicity influences the relationship between these gene polymorphisms and presbycusis phenotypes.

Main Methods:

• A case-control study involving 134 DNA samples.
• Clinical, audiometric, and DNA testing was performed on 55 adults with presbycusis and 79 controls.
• The study was conducted at a university-based tertiary care center.

Main Results:

• The GSTT1 null genotype was associated with a nearly threefold increased risk of presbycusis (OR=2.843).
• The GSTM1 null genotype was more frequent in presbycusis subjects (OR=2.43) and more prevalent in white Hispanics.
• The NAT2*6A mutant genotype was significantly more frequent in presbycusis patients (OR=2.88).

Conclusions:

• White individuals with GSTM1 null, GSTT1 null genotypes, or the NAT*6A mutant allele have an elevated risk of presbycusis.
• The GSTT1 null genotype significantly increases the likelihood of developing presbycusis.
• While GSTM1 null genotype prevalence varied by ethnicity, GSTT1 and NAT2 polymorphisms were similarly distributed.