SINGAPORE – Her rare genetic condition did not just shortchange teenager Jessica Quek’s brain of the two primary chemicals responsible for joy and motivation; it also hijacked her muscle tone.
Yet, the 18-year-old electronics engineering student from ITE College West is not letting it get her down.
In fact, Jessica went against the tide by actively taking part in the annual ITE Inter-College Swimming Meet in 2025 and 2026, taking home two bronze medals across the two meets.
“The first was for the 50m butterfly sprint in 2025 and the one this year was for the 400m breaststroke,” she told The Straits Times.
Even her doctor was pleasantly surprised at her “remarkable accomplishment”.
Jessica competed in the 50m butterfly at the inter-school swimming meet in 2025 and won a bronze medal.
ST PHOTO: LIM YAOHUI
“Knowing that Jessica competed in an interschool swimming meet is a massive testament to early intervention, comprehensive medical care, and her own incredible personal resilience,” said her doctor Mildrid Yeo, a consultant geneticist from the department of genomic medicine at the KK Women’s and Children’s Hospital (KKH).
Jessica was diagnosed with 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, a rare inherited metabolic disorder that results in low muscle tone and impairs the production of serotonin and dopamine in her brain, during newborn screening at KKH.
All newborns at the hospital are screened for metabolic and heritable diseases under the National Expanded Newborn Screening programme, a preventive measure to detect health problems before symptoms appear.
The procedure – which is not legally mandated – involves pricking a baby’s heels to collect a blood sample between 24 and 72 hours after birth.
Yeo said PTPS deficiency occurs when the body cannot produce enough of a “vital helper molecule” called BH4, which is needed by the brain to produce its key chemical messengers.
“Without adequate BH4, three things go wrong at once: an amino acid found in proteins called phenylalanine builds up in the blood and brain; dopamine, the chemical that controls mood and movement, falls short, causing stiffness and motor delays and involuntary tremors similar to those seen in Parkinson’s disease; and serotonin levels drop.
“Serotonin governs mood, sleep and emotional well-being, so low levels can lead to behavioural and cognitive difficulties,” the geneticist said.
“In short, it simultaneously starves the brain of two neurotransmitters at once, which is what makes it so serious if left untreated.”
The condition is “ultra-rare”, affecting approximately one in a million people worldwide, though its prevalence varies significantly by ethnicity and region.
Yeo said the condition is noticeably more common in Asian populations than in Caucasian populations. Currently, there are only three known cases in Singapore, including Jessica.
Early detection gives her a better chance at a normal life
Jessica with KKH consultant geneticist Mildrid Yeo, who manages the teenager’s condition. PTPS deficiency affects the body’s production of BH4, a molecule needed to make key brain chemicals.
ST PHOTO: LIM YAOHUI
Due to her BH4 deficiency, Jessica’s newborn screening detected an excessive amount of phenylalanine, an essential amino acid that is usually found in foods such as meat, fish, eggs, dairy and beans.
Doctors were able to treat her early. Left untreated, the condition could have left Jessica intellectually disabled, with severe developmental delays, and caused seizures.
“Delayed treatment could also result in dystonia, a neurological movement disorder causing muscles to contract involuntarily, leading to twisting movements or abnormal postures,” Yeo said.
“There is no cure for PTPS deficiency, and Jessica’s treatment generally focuses on reducing high levels of phenylalanine and replacing dopamine and serotonin,” she added.
Her low levels of dopamine and serotonin also contributed to her chaotic sleep patterns.
Jessica told ST: “I often fell asleep in class in primary school, especially during Chinese class. My teachers were told of my condition, so there was no issue, nor was I scolded.”
Despite starting medication early, Jessica developed seizures when she turned 10.
She was put on synthetic BH4 to help lower her blood phenylalanine levels. The medication acts as a cofactor, or helper molecule, for multiple enzymes in the body, including the enzyme in the liver responsible for processing phenylalanine.
Yeo said: “But synthetic BH4 alone cannot fix Jessica’s neurotransmitter deficits in the brain. To restore her dopamine levels, she is prescribed levodopa; and for serotonin, she is given 5-hydroxytryptophan to allow the brain to successfully manufacture serotonin.”
Jessica takes more than 10 pills a day to manage her symptoms, but remains upbeat and encourages others to accept their flaws and not be discouraged by the judgment of those around them.
ST PHOTO: LIM YAOHUI
Jessica’s medication costs thousands of dollars a month, and the expense is lifelong, with her medical bill increasing as she grows older.
“We are not rich. My father is a mechanic and my mother a swimming coach,” Jessica said.
The family is financially supported by the Rare Disease Fund, which covers a large portion of her treatment costs.
Jessica, who found out about her condition only when she was 13, added: “I need to take six pills and capsules every morning, two in the afternoon and three at night just to keep my symptoms at bay.”
And kept it at bay she did. The seizures, which started when she was 10, went away in 2023.
Despite her low muscle tone, Jessica continues to swim competitively, some days under her mother’s watchful eye.
She wants to graduate and work as an engineer and “perhaps teach coding in a robotics school one day”.
Despite her condition and the bullying she experienced in primary and secondary schools while growing up, Jessica continues to have a happy outlook on life.
“We should accept our flaws, even when others look down at us for them. Never be discouraged,” she said.