HBV genotyping 12/21/07 Carrie Marshall

Received a send-out request for HBV genotyping on a 52y man

Hepatitis B Genotyping Is this a mistake? What difference does it make? Isn’t everyone getting vaccinated anyway?

While chronic Hep B is not common in the US, there are million patients world wide New studies suggest that the genotype can play a part in the prediction of acute liver disease, development of HCC and/or cirrhosis, and response to antivirals Test requests will likely increase in the future

Hepatitis B Virus is divided into eight genotypes (A through H) based upon genetic variation If there is greater than 8% divergence at the DNA sequence level, then it is a separate genotype The geographical distribution of genotypes is unequal (your genotype depends on your ethnicity and place of birth)

East Asia Types B and C Europe Types A and D India Types A and D Africa Types A, D, and E United States predominately A –West 75% B and C –Southeast 63% A –Midwest 69% A and C

In areas of the world where chronic HBV infection is the most common, there is also less variability of genotypes (hard to see if there is a difference between groups) In the US, where all 8 genotypes are found, there are fewer patients to enroll into studies

Clinical Concerns Patients with chronic HBV have a 15%-25% lifetime risk of developing HCC and/or cirrhosis (NEJM 2004) Who should be monitored? How frequently? How aggressively? (CT, MRI, Bx?) Some evidence that Genotype C has a higher risk for progressing to cirrhosis, and is less responsive to interferon therapy

Natural History of HBV SerologyViral LoadALT level 1. Immune Tolerance eAg +HighNormal 2. Immune Clearance eAg +HighIncreased 3. Carrier State eAg – Anti eAb + Low (<2000 IU) 10 K copies/ml Normal 4. Reactivation e Ag – Anti e Ab + HighIncreased

So what do we want to know about the patient in question? Audience participation

Natural History of HBV SerologyViral LoadALT level 1. Immune Tolerance eAg +HighNormal 2. Immune Clearance eAg +HighIncreased 3. Carrier State eAg – Anti eAb + Low (<2000 IU) 10 K copies/ml Normal 4. Reactivation e Ag – Anti e Ab + HighIncreased

Is that True? Sometimes. That is probably the way it goes for genotypes A and D. Testing for HBVeAg and HBVeAb (~$7.00) is a good way to follow those patients, in combination with ALT But genotypes B and C there is an association with 2 mutations which interfere with the production of HBVeAg

Pre-core mutation will prevent the expression of HBVeAg, without changing the ability of the virus to replicate and is associated with genotypes D (55%), B (44%) and C (22%) Rare in genotype A (3%) Numbers based on a US study Overall in the US, 27% of patients with Chronic HBV have a precore mutation (will not express HBVeAg)

Core promoter mutation can lead to a reduced production of HBVeAg, and is associated with genotypes C (60%), A (41%) and D (40%) Least common in genotype B (26%) Again these are US numbers Overall in the US, 44% of patients with Chronic HBV have a core promoter mutation Mixed results on whether these mutations lead to more injury, or higher viral loads

What does this mean? Should there be a change in the way chronic HBV patients are followed? Should we just follow viral load ($252)? Should everyone get genotyped ($134)? Should patients (or only HBVeAg -) patients be tested for PC/CP mutations?

I don’t know! Serial viral loads would be ideal, but costs a lot more. Maybe just LFTs are good enough? Certainly patients with high viral loads and increased LFTs are at risk for cirrhosis/HCC, but not so clear what the risk is for patients with high viral loads but normal LFTs

Genotyping would be a one-time (?) expense, and could guide the decision to treat, and choice of therapy –Could also predict the likelihood of a PC/CP mutation (and the non-usefulness of following HBVeAg) I couldn’t find convincing evidence that PC/CP mutations have an effect on therapy, and/or risk of cirrhosis and HCC

Related Reading Chu CJ et al. Hepatitis B virus genotypes in the United States: results of a nationwide study. Gastroenterology, 2003;125: Chu CJ et al. Prevalance of HBV precore/core promoter variants in the United States. Hepatology, 2003;38(3):

Related Reading Grandjacques C et al. Rapid detection of genotypes and mutations in the pre-core promoter and the pre-core region of hepatitis B virus genome: correlation with viral persistence and disease severity. Journal of hepatology, 2000;33: Genotype C hepatitis B virus infection is associated with a higher risk of reactivation of hepatitis B and progression to cirrhosis than genotype B: A longitudinal study of hepatitis B e antigen-positive patients with normal aminotransferase levels at baseline. Journal of hepatology, 2005;43: