She lives in darkness and silence because of a genetic condition

SINGAPORE - Life for Ms Tan Siew Ling, 38, an assistant manager in the innovation division at SG Enable, is not only dark, but also silent.

Ms Tan lost her sight when she was 10 and, after fully depending on her hearing thereafter to navigate life, she also lost her auditory sense when she was 32.

“She was around the age of eight or nine when she complained she could not see very well. Thinking it was short-sightedness, our mother took her to the optician to get a pair of glasses made. It did not help her at all,” her brother and primary caregiver Tan Yan Cai, 41, told The Straits Times.

She was then taken to the Singapore National Eye Centre, where she was diagnosed with vision loss due to weak optical nerves. To prepare her for a life of blindness, she went to the Singapore Association Of The Visually Handicapped to learn braille, he said.

Determined not to let her visual impairment hinder her education, Ms Tan completed her secondary education, passed her A levels and pursued a degree in economics and finance at the London School of Economics and Political Science.

“I did so relying on my hearing and with close friends motivating me and cheering me on. I do not want to be a burden to anyone – not friends, not family. With my education and a well-paying job, I would say I am now financially independent,” she said.

However, Ms Tan faced further challenges as her hearing began to deteriorate. In 2016, she lost hearing in her left ear, just a year after her mother’s death. And in 2019, hearing in her right ear was gone too.

Dr Amanda Cheang, who is currently a consultant at the department of otorhinolaryngology at Woodlands Health, said when Ms Tan lost her hearing in her left ear, an MRI scan showed that it was because of a growth on the nerve responsible for hearing.

With her vision loss as a child and hearing loss in adulthood, doctors suspected she had neurofibromatosis Type 2 (NF2), a rare genetic disorder that causes benign tumours to grow on nerves, including those affecting the brain and spinal cord.

The estimated prevalence of NF2 is one in 50,000 people worldwide.

“NF2 is caused by mutations in the NF2 gene located on chromosome 22, which encodes a protein called merlin, which functions as a tumour suppressor. When it is inactive or defective, nerve cells can grow uncontrollably and form tumours,” said Dr Cheang, who is also a visiting consultant at Tan Tock Seng Hospital (TTSH).

Adjunct Associate Professor Yeo Seng Beng, emeritus consultant at TTSH’s department of otorhinolaryngology, said that while the tumours are benign, where they are located and their size can result in debilitating consequences.

For example, tumours compressing the hearing nerves can result in hearing loss, those on the optic nerves may lead to blindness, and those along the spinal cord can result in pain, weakness, or numbness in the arms and legs.

Dr Cheang said in most patients, these tumours grow slowly, so management typically involves periodic scans to monitor for any changes in their size.

“In patients with progressive or rapid growth in tumours, particularly tumours affecting the hearing and balance nerves, bevacizumab can be prescribed as a treatment option. It is given intravenously every few weeks over the course of several months, sometimes extending to long-term use,” said Dr Cheang.

Bevacizumab is a laboratory-made protein that mimics the immune system’s natural antibodies, enabling it to find and bind to a specific target, such as an antigen on a cancer cell or a virus.

Dr Cheang cautioned that careful evaluation is essential before starting this treatment, as it may lead to side effects such as kidney issues and elevated blood pressure.

In Ms Tan’s case, she completely lost her vision due to the benign tumours affecting both optic nerves.

“She then developed bilateral vestibular schwannomas – tumours affecting the nerves responsible for hearing and balance – which led to the profound hearing loss. She also has multiple meningiomas – tumours arising from the lining of the brain – but fortunately, these have not caused any symptoms,” Dr Cheang said.

Said Ms Tan: “I was angry and frustrated. I spent so much time and put in so much effort to maintain my independence, and then (the hearing loss) happened.”

Nevertheless, she expressed gratitude to her close friends and her brother for “rallying in my corner”.

In 2021, Ms Tan underwent right cochlear implant surgery to provide hearing stimulation in her right ear.

Her hearing rehabilitation journey is supported by TTSH staff Jocelynn Khoo, a senior audiologist who programmes her cochlear implant, and Francoise Lim, a principal speech therapist who oversees her post-surgical hearing rehabilitation.

Dr Cheang said: “While we were hopeful that she might regain the ability to understand speech through the implant, we were also mindful that the tumour affecting her right hearing and balance nerve could limit her outcomes compared with most patients.

“After the surgery, she was able to perceive environmental sounds, such as the beeping of MRT doors and approaching footsteps. But, despite intensive rehabilitation, she was unable to achieve clear speech recognition.”

To facilitate communication, her brother, an information technology engineer, discovered a Bluetooth-enabled keyboard that allows words to be translated into braille on a tactile display. Using this device, Ms Tan can “read” what he types and communicate more effectively.

Her groups of friends also take her jogging in the park, creating their own taps and hand signals to keep her safe during their jogs.

“Moving forward, she is being considered for an auditory brainstem implant, a device that sends hearing signals directly to the brainstem, bypassing the tumour affecting her hearing and balance nerve. This will be a more major surgery than the cochlear implant surgery and is still a work in progress,” Dr Cheang said, adding that Ms Tan is now undergoing assessments to evaluate her eligibility for the procedure.

Ms Tan remains uncertain about what lies ahead for her. She admitted, her eyes welling up with tears, that she does not know how to hope or plan, whether for the immediate or distant future.

“I just take life a day at a time, hoping for the best,” she said.