Eight years of outsourced whole-exome sequencing for pediatric-onset rare disease in a Taiwanese tertiary genetics centre: diagnostic yield in 227 patients across five commercial laboratories (2018–2025)

When a child presents with a rare, unexplained illness that begins in early life, doctors often face a long and uncertain journey to find the cause. Many of these conditions stem from tiny errors in a person's genetic code, the instruction manual that tells the body how to build and function. For years, the standard approach was to test for these errors one by one, a slow process that could take years. Today, a technology called whole-exome sequencing has changed the game. This method allows scientists to read the specific parts of the genetic code that are most likely to contain the instructions for making proteins, the building blocks of life. By scanning these sections all at once, doctors can often find the single genetic mistake responsible for a child's complex symptoms, turning a mystery into a diagnosis that can guide treatment and care.

In Taiwan, as in many parts of Asia, hospitals do not usually run these genetic tests themselves. Instead, they send the samples to private companies that specialize in reading the genetic code. This system works, but it creates a unique set of challenges that are rarely discussed in medical reports. A team of researchers at MacKay Memorial Hospital in Taipei decided to look closely at how this system actually functions in the real world. They reviewed eight years of records, tracking 227 children who were referred for this testing between 2018 and 2025. Their goal was not just to see how often the tests found an answer, but to understand the stability and speed of the companies providing the service, and to see what happens when a family relies on a system where the testing provider can change or disappear.

The researchers found that the system works well when it comes to finding answers. Out of the 227 children tested, the doctors were able to document a specific genetic cause for the illness in 91 of them. This means that for roughly four out of every ten children, the test successfully identified the root of their condition. The types of diseases found were incredibly varied, covering everything from problems with how the body processes food to issues with muscle strength, heart function, and brain development. The success rate was high enough to match the best results seen in major hospitals in the West that run their own testing labs. This suggests that even when a hospital outsources the work to a private company, the quality of the genetic reading is high enough to solve complex medical puzzles for children across the entire spectrum of rare diseases.

However, the study revealed that the path to that answer is often bumpy and unpredictable because of how the testing market operates. Over the eight-year period, the hospital worked with five different commercial laboratories. No single company stayed in the lead for more than two years in a row. One company that the hospital had used for several years simply stopped taking their cases after 2022, leaving the doctors to find a new partner without much warning. This constant rotation meant that the hospital had to adapt to different reporting styles and different ways of organizing data every time the primary vendor changed. It is a bit like trying to follow a recipe where the chef changes every few months, each using their own set of measuring cups and writing the instructions in a different handwriting.

The most striking difference between these companies was how long it took to get the results back. For some families, the wait was relatively short, with reports arriving in about a month. For others, the wait stretched out to nearly four months, and in some cases, even longer. The researchers noted that for a sick infant, a delay of three months versus one month can be the difference between having information that helps a doctor act immediately and having information that arrives only after the child's condition has already changed. This wide gap in speed was not due to the complexity of the cases, but simply because different companies worked at different paces. The study highlighted that while the final answer was often correct, the journey to get there was inconsistent.

Another significant finding was that once a report was delivered, the doctors could not easily look back at the raw genetic data to re-check it later. In hospitals that run their own labs, doctors can re-examine the original genetic code years later when new scientific discoveries are made, often finding answers that were missed the first time. In this outsourced model, the hospital only received the final written report. If a new gene was discovered years later, the doctors could not go back and ask the company to re-scan the original sample unless they negotiated special access, which was not standard practice. This limitation means that some children who were initially told they had no answer might have had a diagnosis waiting to be found if the data had been available for a second look.

The researchers concluded that while outsourcing genetic testing to commercial companies is a viable way to diagnose rare diseases in children, it comes with structural costs that need to be acknowledged. The system delivers a high number of correct diagnoses, but it lacks the stability and speed consistency of an in-house service. The study suggests that for this model to truly serve families well, the companies providing the service need to offer more reliable timelines, stay consistent in their partnerships, and agree to share the raw genetic data so that doctors can re-analyze it in the future. Until these structural issues are addressed, families in Taiwan and similar regions may continue to face a diagnostic journey that is successful in finding answers, but unpredictable in how long it takes and how complete the information remains over time.