15q26-qter Deletion Syndrome

If you’ve just heard the diagnosis “15q26-qter deletion syndrome” or seen it on a test result, an unfamiliar term like this can feel unsettling.

Here is the short answer first. This condition is caused by the loss of the region from the middle of the long arm “26” of chromosome 15 all the way to its tip (the telomeric end, or “qter”), and only a few dozen cases have ever been reported worldwide, making it an extremely rare chromosomal disorder. A shortage of the IGF1R gene, one of the growth-related receptor genes in this region, is the main driver behind prenatal growth delay and short stature, while some cases — depending on how much of the chromosome is missing — also involve heart defects or diaphragm abnormalities.

This article walks through the chromosomal change that causes the condition, how it differs from other chromosome 15 disorders (Prader-Willi syndrome, and the mirror-image condition, 15q26 overgrowth syndrome), the symptoms, inheritance patterns, its relationship to prenatal diagnosis and NIPT, the path to a definitive diagnosis, and the outlook for treatment — all based on public and academic sources including GARD, Orphanet, and peer-reviewed case reports. Let’s go through it one step at a time.

1. What Is 15q26-qter Deletion Syndrome? (The Chromosomal Change Behind It)

This condition occurs when everything from somewhere within band 26 of the long arm of chromosome 15 through to its tip (the telomeric end) is missing from birth. “Qter” is chromosome-mapping shorthand for the terminus of the long arm (q). So the name “15q26-qter” describes a continuous loss of material running from around band 26 of the long arm of chromosome 15 all the way to its end.

The size of the deletion varies from case to case. The U.S. National Institutes of Health’s rare disease information center, GARD (Genetic and Rare Diseases Information Center), describes it as a rare chromosomal disorder characterized by prenatal and postnatal growth failure, developmental delay, and intellectual disability. The European rare disease database Orphanet (ORPHA:1596, Distal deletion 15q) lists its prevalence as fewer than 1 in 1,000,000, underscoring just how rare it is.

A case report published in 2021 found 36 genes within this region, of which four are considered most closely tied to symptoms: IGF1R, NR2F2, CHD2, and MEF2A. Of these, the IGF1R (insulin-like growth factor 1 receptor) gene is the one most consistently linked to the clinical picture. The same paper’s literature review found roughly 58 reported cases of a “pure deletion” worldwide to date — this is by no means a common condition.

2. How It Differs From Similarly Named Conditions (Three Easily Confused Diagnoses)

Several conditions are linked to chromosome 15, and even within the “same” chromosome, the location and direction of the change (deletion vs. duplication) can produce completely opposite symptoms. Here’s how the easily confused diagnoses compare.

Condition	Location on the chromosome	Direction of change	Main features
15q26-qter deletion syndrome (this article)	Long arm, band 26 to the tip	Deletion (missing material)	Growth failure and short stature from IGF1R deficiency
15q26 overgrowth syndrome	Long arm, band 26 (near the tip)	Duplication (extra material)	Overgrowth and tall stature from excess IGF1R
Prader-Willi syndrome / Angelman syndrome	Long arm, bands 11-13 (closer to the center of the chromosome)	Deletion (symptoms differ by parent of origin)	Overeating and obesity, or severe developmental disability — an entirely different region from 15q26

A baby typically inherits one copy of the genetic material at any given location from each parent, for two copies in total. If one copy of the 15q26 region is missing, IGF1R activity drops to half, and growth is suppressed. Conversely, an extra copy pushes IGF1R activity above normal, and growth is accelerated. We cover this “mirror image” condition, 15q26 overgrowth syndrome, in a separate article, so please take a look at that too.

Beyond the genetic distinctions and the relationship to prenatal diagnosis and NIPT, this article also covers when growth hormone therapy might be considered and practical tips for daily life.

3. Main Symptoms (Severity Depends on the Extent of the Deletion)

Where the deletion begins (its breakpoint) determines which genes are lost, so the combination and severity of symptoms differs from person to person. Based on the 2021 case report and a separate 2008 case report, the following features have been described.

Symptom / feature	What has been reported
Growth delay starting in the womb (intrauterine growth restriction)	A core feature; babies are often small for gestational age (SGA) at birth
Short stature and poor weight gain after birth	The central symptom from IGF1R deficiency; growth is slow even when appetite is normal
Developmental delay / intellectual disability	Ranges from mild to severe
Microcephaly and distinctive facial features (an inverted-triangle-shaped face, a broad nasal bridge, etc.)	Reported consistently across multiple case reports
Limb features (clinodactyly, underdeveloped nails, etc.)	Relatively common among reported cases
Congenital heart disease (e.g., atrial septal defect)	More frequent in cases with a larger deletion that includes NR2F2
Congenital diaphragmatic hernia	Reported in a subset of cases where the breakpoint falls near 15q26.1-15q26.2

It’s important to note that diaphragmatic hernia does not occur in every patient. The 2008 case report cited above (PMC2248164) narrows the region associated with diaphragmatic hernia down to “the distal end of 15q26.1 through the start of 15q26.2.” If a deletion’s breakpoint falls further toward the tip than that (a region containing only IGF1R), it is not unusual for diaphragmatic hernia to be absent. Please review the extent of the deletion noted in your report together with your physician.

4. Causes and Inheritance Patterns (De Novo vs. Familial Transmission)

Most cases arise from a spontaneous (de novo) change, and the implications for a future pregnancy vary by family.

De novo (spontaneous) cases

This deletion can occur by chance during the formation of sperm or eggs, or during early cell division shortly after fertilization. In the 2021 case report mentioned above, both parents had normal chromosomes, confirming that the change was de novo. It is not caused by anything about the mother’s diet or lifestyle during pregnancy. I always tell patients in my clinic that there is no reason to blame yourself.

Cases passed down within a family

In rare cases, one parent silently carries a balanced chromosomal translocation (a rearrangement where the total amount of genetic material is unchanged, but its order is shuffled), and when that rearrangement is passed on in an unbalanced form, it appears as a deletion in the next generation. In this scenario, the theoretical chance that the deletion is passed on to a future child is about 50% (a pattern similar to dominant inheritance). Chromosome testing of both parents is useful for accurately understanding your family’s inheritance pattern.

If you’re concerned about the implications for a future pregnancy, genetic counseling with a certified clinical geneticist or genetic counselor is worth considering. Even just knowing both parents’ test results can make it easier to plan ahead for your next pregnancy.

Cases involving a ring chromosome (Ring 15)

In rare cases, both ends of chromosome 15 break and fuse together to form a ring-shaped structure known as “ring chromosome 15 (Ring 15),” which results in the loss of genes at the end of the long arm. Even when a microarray test identifies a deletion, an additional microscope-based karyotype test (G-banding) can confirm whether a ring formation is present. If your physician suggests additional testing, it’s worth asking what they’re checking for.

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5. Relationship to Prenatal Diagnosis and NIPT

A deletion in the 15q26-qter region is not part of standard NIPT, and even among expanded panels that screen for microdeletions, only a limited number of providers specifically name it as a target.

Standard basic NIPT primarily screens for changes in the “number” of chromosomes — trisomy 21, 18, and 13. Some expanded panels also cover relatively common microdeletions, such as 22q11.2 deletion syndrome, but because the 15q26-qter region is estimated by Orphanet to occur in fewer than 1 in 1,000,000 people, most testing providers do not include it in their standard scope. It’s worth confirming the exact scope of the plan you’re considering ahead of time.

Here at Hiro Clinic NIPT, we sometimes hear from patients who say an ultrasound showed growth delay (SGA) and they’re worried it might reflect a chromosomal change. The first thing to understand is that NIPT is only a non-definitive screening test.

The Japan Society of Obstetrics and Gynecology’s guidelines on NIPT likewise state that NIPT results remain within the scope of screening (non-definitive) testing. A definitive diagnosis requires an invasive test such as amniocentesis. When an ultrasound flags fetal growth restriction (FGR/IUGR), the cause may involve not only a chromosomal abnormality but also placental function or other factors. Please don’t rush to a conclusion — work through it one step at a time together with a specialist.

6. The Path to a Definitive Diagnosis

Chromosomal microarray testing (CMA), a detailed genetic test, plays the central role in reaching a definitive diagnosis.

Chromosomal microarray testing (CMA)

This test can detect tiny deletions on the scale of a few kilobases to a few megabases that a conventional microscope-based karyotype test (G-banding) would miss. It reveals, in detail, exactly where a deletion begins and ends, and whether genes such as IGF1R or NR2F2 are included. For more on how amniocentesis and microarray testing relate to each other, see our article on amniocentesis and microarray testing.

Testing the parents

A blood test on both parents can determine whether the deletion is de novo or was passed down through a balanced translocation within the family. This is also an important test when thinking through the outlook for a future pregnancy.

Evaluation after birth

After diagnosis, your child’s overall condition is assessed through a combination of growth chart tracking, an echocardiogram to check for heart disease, an abdominal ultrasound, and developmental testing.

7. Treatment and Support

There is not yet a fundamental treatment that can restore the missing piece of chromosome, but growth hormone therapy, developmental therapy, and other symptom-specific support can help promote growth.

• Considering growth hormone therapy: Recombinant growth hormone (rGH) therapy may be considered for short stature, although its effectiveness varies considerably from person to person.
• Managing heart disease: In coordination with pediatric cardiology, observation or surgery is considered depending on the severity of conditions such as atrial septal defect.
• Developmental support (therapy): Physical therapy (PT), occupational therapy (OT), and speech-language therapy (ST) help support a child’s motor, language, and daily-living development.

Case reports show that the effectiveness of growth hormone therapy varies. In a 2025 case report, a patient with a 15q26.3 deletion that removed the IGF1R gene received nine months of rGH therapy; blood IGF-1 levels rose, but height velocity was not sufficient, and treatment was discontinued. This is not a guarantee of outcome either way — decisions are made in consultation with a pediatric endocrinologist while monitoring progress over time.

Because the combination and severity of symptoms differ so much from person to person, there is no single course that “always” applies to this condition. Care is built up gradually, in consultation with your child’s pediatrician, pediatric endocrinologist, and therapy team, into a support plan tailored to your child.

When growth hormone therapy might be considered

Growth hormone therapy is generally considered from around age three onward, once a child meets the criteria for short stature. In Japan, treatment may be available under an existing indication such as “short stature associated with being born SGA,” and because there are conditions around when treatment can begin, connecting with a pediatric endocrinology specialist early on tends to make things go more smoothly. It’s also worth noting that during monitoring, blood IGF-1 (somatomedin C) levels can sometimes appear higher than expected — a finding thought to reflect the body attempting to compensate for having fewer IGF1R receptors by increasing its growth signal.

Nutritional considerations

During infancy, weak sucking strength can make it hard for a baby to gain weight. Some families use high-calorie formula, offer smaller, more frequent feeds, or supplement with tube feeding as needed to support strength. Rather than forcing larger volumes, work with your physician and a registered dietitian to find the pace that suits your child.

8. Tips for Everyday Life

Even when weight and height gain is slow, small adjustments to your daily approach can ease the burden on your family and bring more peace of mind.

• Don’t turn eating into pressure: When weight gain is slow, it’s easy to feel you have to push your child to eat more. Try viewing a small appetite as simply one feature of this condition, and rather than forcing food, lean on medical formula or nutritional supplements while prioritizing making mealtimes enjoyable.
• Choosing clothing sizes: Because body size is often smaller than a child’s age would suggest, clothes with an adjustable elastic waist or designs that are easy to put on and take off can ease the daily routine.
• Track the growth curve that’s specific to your child: Comparing your child to the average curve in a maternal and child health handbook, or to peers of the same age, can be painful at times. Rather than comparing, work with your child’s doctor to follow how your own child’s growth curve is trending over time.

In my own clinic, I regularly hear concerns about weight gain from families. Please don’t carry this alone — reach out to your pediatrician, therapy team, or a psychologist whenever something is troubling you. Small adjustments, stacked up over time, can make daily life easier for both your child and your whole family.

9. Outlook and Prognosis

Because so few cases have been reported, it’s difficult to state a definitive long-term outlook, and whether heart disease or diaphragm complications are present is considered one of the factors that most affects quality of life.

Some individuals experience only short stature and mild developmental delay, while other reported cases involved heart disease or diaphragmatic hernia requiring especially careful perinatal management. This difference is thought to stem from the extent of the deletion and which genes beyond IGF1R happen to be included.

In my own practice, I sometimes field questions from families of children with rare chromosomal conditions like this one about what to expect for growth going forward. Because case data is still accumulating globally, the outlook is best built up gradually, in ongoing consultation with your physician.

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10. Support for Your Family, and Thinking About a Future Pregnancy

The isolation that comes with a rare condition can weigh heavily, but there are several places to turn for support, including genetic counseling, patient advocacy groups, and public consultation services.

It may be difficult to find another family nearby dealing with the same condition. Even so, connections with other families affected by rare chromosomal conditions, and specialized support through genetic counseling, are both available to you. Leave the medical management to your physicians and therapy team, and let your family’s role be simply to celebrate your child’s small steps of growth together.

If you’re curious about the relationship between NIPT and intellectual disability, this article may help. If you’d like to understand the risks associated with microdeletions in general, our article on the risks of small chromosomal abnormalities is also worth a look.

If you’re considering NIPT for a future pregnancy, the plan you choose will depend on how many microdeletions it covers. If you’re not sure which plan fits your situation, try our Plan Finder. We’re also happy to help over the phone — feel free to call us at 0120-169-629.

Frequently Asked Questions

What does “qter” mean?

It’s chromosome-mapping shorthand for the tip (telomeric end) of the long arm (q). “15q26-qter” describes a continuous loss of material running from around band 26 of the long arm of chromosome 15 all the way to its end.

When can growth hormone therapy start?

It’s generally considered from around age three onward, once a child meets the criteria for short stature. In Japan, treatment may be available under an existing indication such as “short stature associated with being born SGA,” and because conditions apply to the start of treatment, it’s important to connect with a pediatric endocrinology specialist early on.

Is this related to “15q26 overgrowth syndrome”?

The same IGF1R gene is involved, but in opposite ways. In this deletion condition, the IGF1R gene is deficient and growth is suppressed; in overgrowth syndrome, a duplication makes IGF1R excessive and growth is accelerated.

Can NIPT detect a deletion in the 15q26-qter region?

It is not typically part of standard NIPT, and even among expanded panels that screen for microdeletions, only a limited number of providers name it as a specific target. Because NIPT is a non-definitive test, a confirmed diagnosis relies on a definitive test such as amniocentesis if there’s a concern.

Is this hereditary? Could it affect a future child?

Most cases arise from a spontaneous (de novo) change, in which case the recurrence risk for a future child is generally considered low. However, if one parent silently carries a balanced translocation, there is roughly a 50% chance it could be passed on, so it’s worth confirming through genetic counseling.

Is growth hormone therapy effective?

Its effectiveness varies considerably from person to person. In some reported cases, blood IGF-1 levels rose but height growth was not sufficient, leading to discontinuation of treatment — so an outcome cannot be guaranteed either way. Decisions are made together with a pediatric endocrinologist while monitoring progress.

Medical supervision: Dr. Hiroshi Oka — Director-in-Chief and Lab Director, Hiro Clinic (Fukumikai Medical Corporation). A graduate of Keio University School of Medicine, Dr. Oka holds a Ph.D. in Medicine and has passed the national medical licensing examinations of both Japan and the United States. He is one of the few physicians in Japan to hold laboratory director credentials. This article was prepared in line with Japan’s medical advertising guidelines, drawing on public and academic sources including GARD, Orphanet, and peer-reviewed case reports. Reported frequencies and figures are based on a limited number of cases and can vary between sources; please consult your physician for decisions about diagnosis and treatment.