It’s in the genes: Bringing precision to medicine

Published on 22 October 2026

When persistent breathlessness disrupted patient Mr Gan’s recovery from a heart attack, genetic testing helped his care team identify a suitable alternative medication.

At a glance

• More than 4,000 patients have undergone pharmacogenomics testing under the PPGx Clinical Implementation Pilot since 2023.
• The pilot analyses genetic variations across 16 genes known to influence patients’ responses to commonly prescribed medications.
• Findings from the pilot have shown that every patient tested carried at least one genetic variant, while one in five had a variant that could predict an atypical response to one of their prescribed medications.

Mr Gan Chee Hiong, 55, remembers the day he had a heart attack. “It was 13 August 2024, and I was climbing Bukit Timah Hill,” he said.

The IT professional felt unusually fatigued but attributed it to the intense 40km cycle he had clocked just the day before. Through his fitness tracker, he also noticed that his heart rate was low, at just 50 beats per minute.

“However, I didn’t feel any pain — it was not like the dramatic scenes you might see in movies,” he recalled. “Even so, I struggled to get off the trail and make it home.”

Back home, Mr Gan’s heart rate remained slow, and he felt worse than before.

He headed to the Emergency Department at the National University Hospital (NUH) at 10am, where an angiogram revealed that his right coronary artery was completely blocked, while the left coronary artery was 75 per cent obstructed.

As an avid cyclist and marathoner, the news came as a shock to him. Mr Gan was hospitalised for over a week, where he underwent stent placement to treat his blocked arteries. Mr Gan was prescribed Ticagrelor, an antiplatelet medication to reduce the risk of another heart attack, stroke, and blood clots from forming.  

Troubling symptoms that ensued

But instead of providing peace of mind, the medication soon became a source of anxiety for Mr Gan, who was working on his recovery at home.

He began developing frequent episodes of breathlessness, which troubled him greatly. “The breathlessness came on randomly and frequently,” Mr Gan recalled. “I was very scared — even a short walk to a nearby coffeeshop would leave me breathless and needing to stop and rest.”

Over the next six months, Mr Gan went to the Emergency Department at NUH a couple of times for severe breathlessness, where his tests came back normal.

Suspecting that his symptoms might be related to his medication, Mr Gan brought his symptoms up to A/Prof Doreen Tan, Cardiology Specialist Pharmacist at the National University Heart Centre, Singapore (NUHCS), who was overseeing his care.

While breathlessness is a recognised side effect of Ticagrelor, the symptoms may improve or resolve over time in some patients. For Mr Gan, however, the breathlessness persisted, significantly affecting his quality of life.

A/Prof Tan explained that there was an alternative medicine, Clopidogrel, but it may not be suitable for Asians, as more than 60 per cent of the local population carry a genetic variant that makes Clopidogrel less effective.

“We ran a reactive CYP2C19 genetic test for Mr Gan as the turnaround time was faster, and I needed the information quickly to assess his suitability for Clopidogrel,” A/Prof Tan said.

Individuals with certain loss-of-function variants in the CYP2C19 gene may not respond adequately to Clopidogrel.

As Mr Gan did not carry the genetic variant, the team was able to switch him from Ticagrelor to Clopidogrel, to his relief.

Integrating pharmacogenomics into routine care

A strong advocate for pre-emptive pharmacogenomics (PPGx), A/Prof Tan also encouraged Mr Gan to enrol in the PPGx Clinical Implementation Pilot, to undergo wider pharmacogenomics testing.

The pilot is part of a broader effort by the National University Health System (NUHS) to integrate pharmacogenomics into routine care. Conducted as an implementation research programme, it analyses genetic variations across 16 genes known to influence patients’ responses to commonly prescribed medications.

“When you need the drug, your information would already be in the system, which would prompt doctors to give the right medication without ordering separate genetic tests for each drug needed to treat the condition,” said Dr Elaine Lo, Principal Clinical Pharmacist, NUH, who is the lead pharmacist for the pilot.

“This knowledge guides us towards the right drug and the right dose for each individual — bringing us closer to safer and more-personalised treatment from the start.”

Patients receiving care within NUHS are generally eligible for testing, except those who have received a blood transfusion within the past three months or undergone a liver or bone marrow transplant.

These efforts are now being further strengthened through the National University Centre for Genomic Medicine, which was launched in April 2026 to expand genomics testing and support more precise, personalised care across multiple specialties.

To date, more than 4,000 patients have undergone pharmacogenomics testing under the programme. Findings from the pilot have shown that every patient tested carried at least one actionable genetic variant, while one in five had a variant that could predict an atypical response to one of their prescribed medications.

The PPGx Clinical Implementation Pilot aims to integrate PPGx into clinical practice and improve patient outcomes by testing for multiple genetic variants that could influence commonly used medications, such as codeine for pain management, cholesterol-lowering statins, several chemotherapy drugs such as mercaptopurine and antidepressants like sertraline.

A second chance at life

Today, Mr Gan’s life has largely returned to normal, and he has been able to resume moderate exercise. Having benefited from PPGx, he has become a strong advocate, sharing his experience with family and friends.

“I came to understand that there was a solution for me — precision medicine,” he said. “It would be very useful if we could eliminate medication options that are not appropriate for us at the start.”

For Mr Gan, a newly minted grandfather, life has come full circle.

“I was able to fly to Japan to witness the birth of my grandson. He was born on 13 August 2025 — exactly a year after I suffered my heart attack,” he said.

In consultation with A/Prof Doreen Tan, Cardiology Specialist Pharmacist, NUHCS, and Dr Elaine Lo, Principal Clinical Pharmacist, NUH.