HBV Genotyping/HBV Drug Resistance

YMDD Mutation

Introduction - HBV

There are about 350 million persons chronically infected

with HBV worldwide. Chronic carrier rate in India is 4.7%

Chronic HBV infection is associated with a wide range of

clinical manifestations, from an asymptomatic carrier status

with a normal liver histology to severe and chronic liver

disease, including cirrhosis and hepatocellular carcinoma

(HCC).

The virus relies on error-prone reverse transcriptase during

the replicative process due to which mutant viral genomes

are found frequently.

Reverse transcriptase

A reverse transcriptase, also known as RNA-dependent DNA

polymerase, is a DNA polymerase enzyme that transcribes

single-stranded RNA into single-stranded DNA

The enzyme is encoded and used by reverse-transcribing

viruses, which use the enzyme during the process of

replication

Without reverse transcriptase, the viral genome would not be

able to incorporate into the host cell, resulting in the failure of

the ability to replicate

HBV Genotypes:

• HBV is been classified into 8 genotypes (A-H) based on an

intergroup divergence of 8% or more in the complete

nucleotide sequence.

Significance of HBV Genotyping

• HBV genotype C is associated with more severe liver diseases than genotype B.

• Patients infected with genotype D appear to have a higher incidence of HCC, a higher risk for HBV recurrence, and a higher mortality rate after liver transplantation than patients with genotype A.

• Patients with HBV genotypes C and D have a lower response rate to treatment with IFN-a compared to those with genotypes A and B.

• Genotype may also influence the emergence of lamivudine resistance mutations, which appear to be more strongly associated with genotype A than genotype D.

• Therefore, HBV genotyping is of great importance in guiding treatment, improving vaccination, and controlling liver diseases.

HBVDR

• Lamivudine, Telbivudine, Adefovir and Emtricitabine are nucleotide/nucleoside analogues that target the reverse transcriptase activity of HBV polymerase during viral replication.

• Nucleotide/Nucleoside analogue therapy allows safe, long term supression of hepatitis B virus and is a major milestone in the treatment of chronic hepatitis B.

• Early detection of emerging HBV drug resistance mutations helps to monitor lamivudine treatment, and improves therapeutic decision making like use of adefovir rescue therapy.

Amino Acid SLC DNA codons

Isoleucine I ATT, ATC, ATA

Leucine L CTT, CTC, CTA, CTG, TTA, TTG

Valine V GTT, GTC, GTA, GTG

Phenylalanine F TTT, TTC

Methionine M ATG

Cysteine C TGT, TGC

Alanine A GCT, GCC, GCA, GCG

Glycine G GGT, GGC, GGA, GGG

Proline P CCT, CCC, CCA, CCG

Threonine T ACT, ACC, ACA, ACG

Serine S TCT, TCC, TCA, TCG, AGT, AGC

Tyrosine Y TAT, TAC

Tryptophan W TGG

Glutamine Q CAA, CAG

Asparagine N AAT, AAC

Histidine H CAT, CAC

Glutamic acid E GAA, GAG

Aspartic acid D GAT, GAC

Lysine K AAA, AAG

Arginine R CGT, CGC, CGA, CGG, AGA, AGG

Stop codons Stop TAA, TAG, TGA

Y I D D

YMDD – YIDD/ YVDD

YMDD test report @Metropolis

HBVDR test report @Metropolis

HBVDR test report @Metropolis

HBV Genotyping/ HBV-DR

HBV DNA Extn

(Serum/ Plasma)

Nested PCR

(Polymerase Gene) Gel Electrophoresis

HBVG Analysis

(Viral Genotyping Tool)

PCR Sequencing

HBV-DR Analysis

(Mutation Detection)