Genetics vital for medication - Prof. Vajira Dissanayake

By Dhaneshi Yatawara

Medicines have become an integral part of our lives with the increasing number of ailments. At times one would wonder whether the number of drugs is adequate to cure patients. A patient could experience inefficacy of drugs and doctors would put the blame on the patient for being resistant to medicine. This has been prominent particularly in treating cancer patients where the doctors may have to use higher dosages. Whether this was the correct system in treating was a question that persisted. Medical experts have found another reason for the inefficacy of drugs.

According to medical experts patients react in different ways to drugs. As Professor Vajira Dissanayake, Head of the Genetics Department of the Colombo Medical College there are four possible ways a patient reacts. "One instance would be that the drug will be effective and the patient will not have any side effects. The second is the illness will be cured but the patient will have side effects or adverse reactions. The third possibility would be that the patient will not be cured and will have no reactions. The fourth way is that the patient will be cured but with side effects leading to death," Prof. Dissanayake said.

Medical experts call it pharmacogenomics and today it has been termed 'personalised medicine'. "Pharmacogenomics refers to how a person responds to a drug", explained Prof. Dissanayake.

The basis for pharmacogenomics is genetics and as Prof. Dissanayake pointed out a genetic diagnosis can show the most effective medical treatment plan for a particular patient. "Personalised medicine is based on genetic make up. Using genetics to personalise medication is the latest technology to treat patients", he added.

As he further explained varieties under the same generic name can show different responses in different patients - this applies to different regions in the world as well as different people in the same region. So it is essential for the authorities to find out what medicine would suit our genes. For example in US nearly 100,000 people die of drugs prescribed by doctors per year. And 2.5 million people develop adverse reactions according to US estimates. The situation in Europe is similar. In Sri Lanka we do not have statistics. Since we are using similar drugs we can have a similar situation although it may not be so large in numbers since our population is small.

"So are focus now is not just diagnosing inherited disorders but utilising genetics for effective therapy. This is called 'personalised medicine'," he added.

He said that in the past genetics was looked at from the point of view of inherited disorders which could not be cured. But today there are lots of inherited disorders for which although we can not cure there are treatments which would make the conditions mild or less lethal. "At the same time genetics is becoming more relevant in common conditions as well. And one area where it is going to be relevant is in the area of pharmacogenomics," he said.

"We are using the concept of personalised medicine in the country particularly in treating cancer," Prof. Dissanayake added. For example for treating colorectal cancer after the tumour is taken out there is a treatment called Anti EGFR therapy which most patients need to take. Before a patient undergoes therapy for cancer the test is done to identify mutant genes in a gene called KRAS gene.

When you test for that and if the mutation is there then there is no point in treatment. The patient would not respond to the therapy," Prof. Dissanayake explained. The course of treatment would cost around Rs. 120,000 or more. And mind you colorectal cancer is one of the top ten cancers in Sri Lanka and every year as per statistics 700 - 800 patients develop colorectal cancer. The patient or the Government will be just wasting money if the patient is not going to respond to the treatment. We have been doing this for the past two three years in our medical system. And patients have benefited from that. So that is one aspect, he added.

What happens more commonly in cancers is that the patient gets a mutation in the tumour. And that is which drives the cancer. So here KRAS mutation is one of those. If a patient has that mutation even the conventional treatment would not work for you.

Another example is in certain types of Leukaemia, there is a gene called Philadelphia chromosome. If positive for the gene there are certain drugs that can block that. They are medically called thyroxine kinasine inhibitors. So in such situations pharmacogenomic markers can introduce treatments to suit the patient's condition.

Another instant is using this to the medicine called 'waferine'. This is given to patients who have under gone strokes or heart conditions. If this drug is overdosed it can cause bleeding. In many western countries most of the patients admitted for emergency treatment are those overdose with waferine. We can look at the genetics of a person and prescribe the correct dose. Genetics can be used to tailor made medical treatment.

Prevention

Considering prevention for example if a certain family has a history of breast cancer perhaps there is a possibility of inherited conditions to cancer. And then we can test an affected person in the family and then after testing if found that the patient has mutation then there is a high risk for the other family members contracting it.

"These sort of information is circulated at places like the Cancer Hospital but very few patients come for treatment. The genetic tests are done at the Department of Genetics of the Colombo University Medical College," said Prof. Dissanayake.

As he further explained one of the main problems is that the genetic testing is expensive. For example if a patient needs to get genetically tested for breast cancer in a Western country it would cost around Rs.300,000. "In Sri Lanka we do the same test for about Rs.75,000. But still that can be expensive to many patients. So we are in the process of reducing that cost as well through new technology", he added.

Inherited diseases in genetics will be confined to few people but topics like pharmacogenetics can be applied to all people, said Prof. Dissanayake. What we are trying to do is to make these tests more cost-effective. But the technology is developing only now. And hopefully we will be able to optimize the technology where we can for the benefit of the people, he said.

Do we have sufficiently developed technology to promote pharmacogenetics in the country? "We are in the process of acquiring that technology," said the Professor. "Government is also keen on acquiring this technology and popularising the facility. But funding is the biggest problem. We are planning to set up a comprehensive facility for genetics diagnostics," he added. "Government has given a 300% tax incentive for the private sector to invest in research and development which is a positive step.

The lack of awareness of doctors on the importance of genetics in prescribing medicine is a major problem said Prof. Dissanayake. Even in the US according to statistics it was revealed that five percent of the oncologists use the KRAS test before treating colorectal cancer patients.

Even in developed countries this is the situation. So there is a need to retrain our doctors as well. So we need to look at strategies in increasing the number of doctors getting involved with postgraduate studies and training programs in genetics. "That is what we are trying to do right now. And we plan to create a pool of doctors who can train other doctors", said Prof. Dissanayake.