Reading a Baby's Whole Genome: How a Single Test Can Change a Newborn's Care

What the NICUSeq study (published in JAMA Pediatrics in 2021) showed about using whole-genome testing for very sick newborns

When a newborn is seriously ill and doctors suspect the cause might be genetic, a test that reads nearly all of the baby's DNA can change the care that baby receives. A large 2021 study called NICUSeq followed 354 critically ill infants at five US children's hospitals and found that when doctors had whole-genome sequencing results in hand, twice as many babies had a meaningful change in their treatment plan compared with babies whose results had not yet come back. The change might mean starting the right treatment, choosing the right specialist or surgery, or stopping a treatment that was never going to help. This article explains what the study did, what it found, and what it means for families.

Why this question mattered

Some babies arrive in the neonatal intensive care unit, or NICU, with problems that are hard to explain — unusual physical differences, seizures, heart defects, or a combination that doesn't fit a simple diagnosis. For a long time, finding out whether a baby had an underlying genetic condition meant a slow, step-by-step series of tests. Doctors might start with a test that looks at a baby's chromosomes, then move to tests for specific genes, adding other studies along the way. Each step took time, and a clear answer often came only after the most important decisions had already been made — or sometimes never came at all. For families, that uncertainty is exhausting, and for doctors it can mean treating a baby without knowing what they are truly treating [1].

As technology improved, hospitals gained the ability to read a baby's DNA much more completely and quickly. Two related tools became available: one reads the small fraction of DNA that contains most known disease-causing genes, and a broader one — whole-genome sequencing — reads nearly all of a person's DNA. Early hospital experiences were promising. When doctors used these tools on very sick infants, they found a genetic explanation in roughly a third of carefully chosen babies, and in about half of those cases the diagnosis changed something about the baby's care [2]. Some of the earliest experience using rapid whole-genome testing in intensive care units showed that most of the diagnoses it uncovered led doctors to manage babies differently [3]. Other early programs even suggested these tests could reduce how sick babies became and lower the cost of their hospital stays [4].

But there was a catch. Almost all of this earlier evidence came from studies without a fair comparison group. When a baby's care changes after a test, it is hard to know whether the test caused the change or whether the baby's care would have changed anyway as time passed. To really know whether whole-genome sequencing makes a difference, researchers needed a carefully designed study that compared similar babies — and that is exactly what NICUSeq was built to do [1].

How the study worked

The researchers faced an ethical challenge. If a test might genuinely help a critically ill baby, it feels wrong to deny it to some babies just to create a comparison group. So they used a clever and fair approach called a time-delayed design. Every one of the 354 babies in the study received whole-genome sequencing — none were denied the test. The babies were simply randomly assigned to receive their results at one of two times: an "early" group got results about 15 days after joining the study, and a "delayed" group got results about 60 days after joining [1]. During the study, every baby's medical team continued ordering whatever other tests they normally would. This let researchers compare, at the 60-day mark, the babies whose doctors already had genome results against those whose results had not yet arrived.

The babies in the study were genuinely sick and came from diverse backgrounds that reflected the broader US population. Most were newborns — the average age was about two weeks — and most were cared for in the NICU. The most common reason for testing was that a baby had several physical differences present at birth. To be included, a baby had to be under four months old, in an intensive care unit, with objective signs suggesting a genetic cause, and at least one parent had to take part so the lab could compare the baby's DNA with a parent's. Using parents' DNA alongside the baby's helps the laboratory tell harmless differences from meaningful ones — an approach refined in studies of rapid sequencing in sick infants [5]. This kind of testing has even been shown to be practical within national health systems [6].

What they found

The main result was clear. At the 60-day mark, twice as many babies in the early group had a change in their care because of what the genome test revealed: about 21 out of every 100 babies in the early group, compared with about 10 out of every 100 in the delayed group [1]. The early group was also twice as likely to have received a precise diagnosis. The most convincing part came next: once the delayed group finally received their results, their rate of care changes doubled too — even though more than two months had gone by. The plan changed when the answer arrived, not simply because the babies grew older. This pattern is what gives confidence that the test itself was responsible.

What kinds of changes happened? Most were the everyday substance of good medical care, made sharper by knowing the diagnosis. The most common change was referring a baby to the right specialist. Others included choosing a surgery or procedure, starting a medication aimed at the specific condition, or adjusting other medicines [1]. Two real examples from the study show the range. One baby boy was found to have a serious immune-system condition called Wiskott-Aldrich syndrome and went on to receive a bone marrow transplant that could correct it. Another baby girl with seizures was found to have a specific genetic form of epilepsy; once her doctors knew this, they were able to stop an unnecessary set of tests and a vitamin treatment that would not have helped her. Knowing the answer can mean starting the right care — and it can also mean confidently stopping the wrong care, which spares a baby and family needless procedures.

The study also offered reassuring and practical details. Genetic answers were found across many kinds of babies, including some born very prematurely — a reminder that not every problem in a premature baby is caused by prematurity alone [1]. Overall, about a third of the babies eventually received a genetic diagnosis, and among those diagnosed, roughly two-thirds had some change in their care. This fits with what other prospective programs have reported when sequencing is used early [7], and with randomized work comparing different sequencing approaches [8].

It is just as important to be honest about what the study did not show. Over its roughly three-month window, the babies who got their results early did not have shorter hospital stays or better survival than those who got results later [1]. So the clearest benefit of the test is a faster, more precise understanding of what is wrong and more focused care — not, on this evidence, a guarantee of a shorter stay or a saved life. Researchers also noted that three months may be too short to capture all the ways a diagnosis shapes a child's care over time, so the full benefit is likely larger than the study could measure.

What this means for families

If your baby is in the NICU and the team suspects a genetic condition, this study supports asking about whole-genome sequencing earlier rather than as a last resort. A diagnosis can do several things at once: it can point toward a specific treatment, connect your family with the right specialists, end a long and stressful search for answers, and help everyone plan for what comes next. Because the test usually works best when parents' DNA is included, you may be asked to give a simple sample too. The test can also occasionally reveal unexpected health information about your baby — or even about the family — so hospitals offer genetic counseling before and after testing to help families understand and decide what they want to know, following national professional guidance [9].

It is also worth knowing that a "negative" result does not always mean there is no genetic cause; some conditions are not detectable by this test, and our understanding of genes keeps growing. Major medical organizations now recommend genome and exome testing as an early option for children with birth differences or developmental concerns, reflecting how strong the overall evidence has become [10], and large reviews confirm these tests find answers more often than older methods [11].

What researchers are working on next

Scientists are now studying how to make results come back even faster, how to make sure every family — regardless of background or where they live — has equal access to this testing, and how a diagnosis affects a child's health over years rather than months. They are also refining how to handle the extra health information these broad tests can uncover, so families receive it thoughtfully and with support [12]. For families facing the uncertainty of a critically ill newborn, the direction of this research is hopeful: a single test, used early, can turn a long search into a clear answer, and a clear answer into better care.

References

  1. The NICUSeq Study Group. Effect of Whole-Genome Sequencing on the Clinical Management of Acutely Ill Infants With Suspected Genetic Disease: A Randomized Clinical Trial. JAMA Pediatrics. 2021;175(12):1218–1226. doi:10.1001/jamapediatrics.2021.3496 ↩
  2. Meng L, Pammi M, Saronwala A, et al. Use of Exome Sequencing for Infants in Intensive Care Units: Ascertainment of Severe Single-Gene Disorders and Effect on Medical Management. JAMA Pediatrics. 2017;171(12):e173438. doi:10.1001/jamapediatrics.2017.3438 ↩
  3. Willig LK, Petrikin JE, Smith LD, et al. Whole-genome sequencing for identification of Mendelian disorders in critically ill infants: a retrospective analysis of diagnostic and clinical findings. Lancet Respiratory Medicine. 2015;3(5):377–387. doi:10.1016/S2213-2600(15)00139-300139-3) ↩
  4. Farnaes L, Hildreth A, Sweeney NM, et al. Rapid whole-genome sequencing decreases infant morbidity and cost of hospitalization. npj Genomic Medicine. 2018;3:10. doi:10.1038/s41525-018-0049-4 ↩
  5. Kingsmore SF, Cakici JA, Clark MM, et al. A Randomized, Controlled Trial of the Analytic and Diagnostic Performance of Singleton and Trio, Rapid Genome and Exome Sequencing in Ill Infants. American Journal of Human Genetics. 2019;105(4):719–733. doi:10.1016/j.ajhg.2019.08.009 ↩
  6. Australian Genomics Health Alliance Acute Care Flagship. Feasibility of Ultra-Rapid Exome Sequencing in Critically Ill Infants and Children With Suspected Monogenic Conditions in the Australian Public Health Care System. JAMA. 2020;323(24):2503–2511. doi:10.1001/jama.2020.7671 ↩
  7. Stark Z, Tan TY, Chong B, et al. A prospective evaluation of whole-exome sequencing as a first-tier molecular test in infants with suspected monogenic disorders. Genetics in Medicine. 2016;18(11):1090–1096. doi:10.1038/gim.2016.1 ↩
  8. Dimmock D, Caylor S, Waldman B, et al. Project Baby Bear: Rapid precision care incorporating rWGS in 5 California children's hospitals demonstrates improved clinical outcomes and reduced costs of care. American Journal of Human Genetics. 2021;108(7):1231–1238. doi:10.1016/j.ajhg.2021.05.008 ↩
  9. Miller DT, Lee K, Chung WK, et al. ACMG SF v3.0 list for reporting of secondary findings in clinical exome and genome sequencing: a policy statement of the American College of Medical Genetics and Genomics (ACMG). Genetics in Medicine. 2021;23(8):1381–1390. doi:10.1038/s41436-021-01172-3 ↩
  10. Manickam K, McClain MR, Demmer LA, et al. Exome and genome sequencing for pediatric patients with congenital anomalies or intellectual disability: an evidence-based clinical guideline of the American College of Medical Genetics and Genomics (ACMG). Genetics in Medicine. 2021;23(11):2029–2037. doi:10.1038/s41436-021-01242-6 ↩
  11. Clark MM, Stark Z, Farnaes L, et al. Meta-analysis of the diagnostic and clinical utility of genome and exome sequencing and chromosomal microarray in children with suspected genetic diseases. npj Genomic Medicine. 2018;3:16. doi:10.1038/s41525-018-0053-8 ↩
  12. Petrikin JE, Cakici JA, Clark MM, et al. The NSIGHT1-randomized controlled trial: rapid whole-genome sequencing for accelerated etiologic diagnosis in critically ill infants. npj Genomic Medicine. 2018;3:6. doi:10.1038/s41525-018-0045-8 ↩