15q13.3 Deletion Syndrome (BP4 to BP5)

What Is 15q13.3 Deletion Syndrome?

15q13.3 deletion syndrome is a very rare congenital condition caused by the loss of part of the genetic material in the region from BP4 to BP5, within band q13.3 on the long arm of chromosome 15. This region contains six genes — MTMR15, TRPM1, MTMR10, KLF13, OTUD7A, and CHRNA7 — and the activity of CHRNA7 in particular is thought to be strongly linked to the symptoms. Let’s start with the overall picture of the condition.

A “microdeletion” refers to the loss of a very small segment of a chromosome. These are often too small to detect with conventional microscope-based chromosome analysis, and are frequently only identified through more detailed testing. “BP4” and “BP5” are simply labels for the breakpoints marking the edges of this region. Even among people with a deletion in the same BP4–BP5 range, the exact size of what is missing can differ from person to person.

How Rare Is This Condition?

15q13.3 deletion syndrome is extremely rare in the general population, and a precise prevalence figure has not yet been firmly established. However, studies of people with idiopathic generalized epilepsy, a specific epilepsy subtype, have reported this deletion at a clearly higher rate than in healthy control groups. Japanese proposed diagnostic criteria note that intellectual disability is seen in more than half of reported cases, and seizures in roughly 28%.

Numbers alone can sound alarming, but a defining feature of this condition is that a meaningful number of people have no symptoms at all. It helps to keep in mind that this condition is rare enough that its frequency can’t be pinned down precisely, and that individual variation is large — that combination is what makes a calm, grounded understanding possible.

Deletion (Loss) vs. Duplication (Gain) — Don’t Confuse the Two

Chromosomal changes broadly fall into two categories: deletion and duplication. A deletion (loss) means genetic material is missing; a duplication (gain) means there is extra genetic material. Even within the exact same BP4–BP5 range of 15q13.3, a deletion and a duplication are treated as entirely different conditions.

This article covers 15q13.3 deletion syndrome — the “loss” type. The “gain” type, in which genetic material in the same region is duplicated instead, is a separate condition known as 15q13.3 duplication syndrome (covered in a companion Japanese-language article: 15q13.3 duplication syndrome). Duplication syndrome tends to show a wider range of symptom presentations than deletion syndrome, and many people with it have no symptoms at all. If you or your child has been tested, check your test report to see whether it specifies a deletion or a duplication.

Main Symptoms — Epilepsy, Intellectual Disability, and Autism Spectrum Disorder

The main features associated with 15q13.3 deletion syndrome are epilepsy, intellectual disability or developmental delay, autism spectrum disorder, and an increased risk of psychiatric conditions such as schizophrenia and bipolar disorder — and both which symptoms appear and how severe they are vary enormously from person to person. Not everyone shows every feature, and some people have no noticeable symptoms whatsoever. Here is an overview of the most commonly reported features.

Epilepsy (and Its Link to Idiopathic Generalized Epilepsy)

Epilepsy is one of the best-studied features of this condition. Studies of people with idiopathic generalized epilepsy have found a clearly higher rate of 15q13.3 deletions than in healthy individuals. Seizure type and severity vary widely from person to person.

When epilepsy is identified, treatment moves forward together with a pediatric neurologist or neurologist, using anti-seizure medication matched to the seizure type. Keeping a log of seizures makes it easier to share what’s happening with the care team at each visit.

Intellectual Disability, Developmental Delay, and Autism Spectrum Disorder

Intellectual disability is reported in more than half of documented cases. It tends to be mild to moderate, but some people have intellectual development that falls within a broadly typical range. A tendency toward slower language and communication development has also been reported.

Traits related to social communication associated with autism spectrum disorder can also be present. For more on how intellectual development connects with pregnancy-related questions in general, see our related Japanese-language article, Intellectual Disability Risk and Pregnancy.

Psychiatric Risk, and Why Some People Have No Symptoms

From adulthood onward, the risk of psychiatric conditions such as schizophrenia and bipolar disorder is reported to be somewhat elevated. This does not mean these conditions are certain to develop. Ongoing monitoring over time, together with a care setup that allows for early consultation if something feels different, can make a real difference.

This is where the concept of “incomplete penetrance” matters. Even among people with the exact same deletion, a meaningful number show no noticeable symptoms at all. That degree of individual variation is part of what makes 15q13.3 deletion syndrome hard to fully pin down — and, at the same time, it’s a source of real reassurance.

Cause — the CHRNA7 Gene and Incomplete Penetrance

The symptoms of 15q13.3 deletion syndrome are thought to be largely driven by reduced function of the CHRNA7 gene, which encodes the alpha-7 subunit of a nicotinic acetylcholine receptor in the brain. Several other genes also lie within the deleted region, but a shortage of CHRNA7 gene dosage (haploinsufficiency) is considered the central driver of the symptoms.

The inheritance pattern is autosomal dominant with incomplete penetrance. Reports indicate that roughly 75% of these deletions are inherited from one parent, and that parent frequently has no obvious symptoms, or only very mild ones. The remaining cases arise as new (de novo) changes, for example during the formation of sperm or egg cells.

In genetic counseling, I have repeatedly met parents who blame themselves, feeling that their child’s serious symptoms must be “their fault.” But because penetrance is incomplete, it is entirely possible for a parent with no symptoms to have a child with more pronounced symptoms. That outcome is nobody’s fault — it is simply how this form of inheritance works.

If you’d like a clearer picture for future family planning, chromosomal microarray testing of both parents can determine whether the deletion was inherited or arose as a new mutation. If this concerns you, please speak with a specialist through genetic counseling.

Diagnosis — Confirmed by Chromosomal Microarray Testing

15q13.3 deletion syndrome is confirmed through chromosomal microarray testing, which can detect very small chromosomal deletions or duplications. Subtle changes that are hard to detect with conventional microscope-based chromosome analysis (karyotyping) can be picked up with this test. Here is how prenatal and postnatal testing pathways each work.

Where This Fits Among Prenatal Tests (Its Relationship to NIPT)

There’s an important point worth knowing upfront. NIPT (non-invasive prenatal testing) is a non-definitive screening test that primarily looks at numerical chromosomal changes such as trisomy 13, 18, and 21. A microdeletion like 15q13.3 is not part of standard NIPT. Some clinics offer it as an optional expanded-panel item, but the range covered is limited and detection rates vary.

Because of this, even if an optional expanded test reports “elevated probability,” that alone does not confirm a diagnosis. This is not a test that can promise unlimited accuracy — that’s an important point to keep in mind. For the full picture of what standard NIPT does and does not cover, see our related Japanese-language article, Conditions NIPT Can Detect. For more on how microdeletion syndromes in general relate to NIPT, see Microdeletion Syndromes and NIPT.

A Definitive Diagnosis Requires Amniocentesis or Chorionic Villus Sampling

A definitive diagnosis is made by taking cells collected through amniocentesis or chorionic villus sampling and examining them with chromosomal microarray testing. These are definitive, diagnostic tests, but they carry a small risk of miscarriage — reported at roughly 0.3% for amniocentesis and roughly 1% for chorionic villus sampling.

Whether to proceed is a decision for each family to make, weighing that risk against the value of the information gained. Details on the definitive test itself are covered in our related Japanese-language article, About Amniocentesis. After birth, chromosomal microarray testing can be done from a simple blood draw, with no miscarriage risk involved.

Test	Category	Relevance to 15q13.3 Deletion	Physical Burden
NIPT (non-invasive prenatal testing)	Non-definitive screening test	Not part of standard NIPT. Offered as an optional expanded item at some clinics; coverage and detection rates vary	Blood draw only
Amniocentesis + chromosomal microarray	Definitive diagnostic test	Can confirm the precise extent of the deletion	Miscarriage risk approx. 0.3%
Chorionic villus sampling + chromosomal microarray	Definitive diagnostic test	Can confirm the diagnosis earlier in pregnancy	Miscarriage risk approx. 1%
Postnatal blood test + chromosomal microarray	Definitive diagnostic test	Can confirm the diagnosis after birth	Blood draw only

Approaching the Decision About Prenatal Testing

There is no single right answer to whether you should undergo prenatal testing — choosing to test and choosing not to are both meaningful, valid decisions for a family to make. Feeling torn is completely natural. Here we look at how other people have thought it through, drawing on real voices from those who have faced this decision.

In counseling sessions, I have often heard people say, “I was sure I’d have NIPT, but once I actually got pregnant, I hesitated.” On X, @sisisi195275806 wrote candidly about having been fully intending to get NIPT, then feeling deeply torn once pregnant — and being glad, in the end, that she went through with it. The process of wavering and working through the decision is, in itself, a way of engaging with your baby.

Other people, after much thought, decide not to test at all this time. On X, @mmy338 wrote about wrestling with the decision over prenatal testing and arriving at the conclusion that, this time, she would not pursue it. A decision not to test, reached after real reflection, is just as legitimate a choice — and it isn’t for anyone else to rank one decision above the other.

If you’re torn, please don’t carry it alone — genetic counseling gives you a chance to talk it through with a specialist. Together, you can sort out what a test can and can’t tell you, and what your options are afterward. Our related Japanese-language article on how one family worked through this decision, a family’s testing consultation case study, may also be a useful reference.

Managing Epilepsy and Developmental / Medical Support

There is no treatment that cures 15q13.3 deletion syndrome itself, but combining epilepsy management with developmental support can meaningfully help a child thrive. Support is typically provided by a team of specialists, matched to each child’s specific combination of features. Here are the main pillars of support.

When epilepsy is present, care continues in partnership with a pediatric neurologist or neurologist, using anti-seizure medication matched to seizure type. Recording the frequency and pattern of seizures helps with fine-tuning medication. For children whose motor or language development is progressing slowly, physical therapy, occupational therapy, and speech therapy can all be valuable.

When traits associated with autism spectrum disorder are present, behavioral support and coordination with local developmental support services or special-needs education are also options worth considering. From adulthood onward, an ongoing relationship with a primary care physician helps changes in mood or behavior get noticed and addressed early.

If you’re not sure where to start, your child’s pediatrician or your local public health center is a good first stop — from there, you can be connected to the right resources for epilepsy, development, or behavioral support.

Support for Families and Where to Turn for Help

Because this is such a rare condition, knowing about public consultation services and diagnostic-criteria resources early on can be a real source of support so families don’t feel isolated. Long-term medical care and developmental support take time and emotional energy. Here are some resources worth knowing about.

For information on rare and intractable diseases (in Japanese), Japan’s Center for Intractable Disease Information is a useful resource. For developmental support, Japan’s National Rehabilitation Center for Persons with Disabilities — Developmental Disability Information and Support Center outlines where to find consultation and support. Japanese specialists’ proposed diagnostic criteria are also summarized in this academic reference on 15q13.3 microdeletion syndrome (Japanese, PDF). For neutral background on prenatal testing itself, Japan’s Japanese Association of Medical Sciences Committee on Prenatal Testing Certification is another helpful resource.

Closer to home, local public health centers, child development support centers, and family support groups made up of people with similar experiences can all make a real difference. Connecting with families walking a similar path makes it easier to share day-to-day strategies and process feelings together. Financial assistance programs for medical care and developmental support may also be available, so it’s worth checking with your local municipal office.

Frequently Asked Questions

Q. Can NIPT detect 15q13.3 deletion syndrome?

This microdeletion is not part of standard NIPT (non-invasive prenatal testing). Some clinics offer it as an optional expanded-panel item, but the range covered is limited and detection rates vary. Because NIPT is a non-definitive screening test, an elevated probability result alone does not confirm a diagnosis. A definitive diagnosis requires chromosomal microarray testing of cells collected through amniocentesis or chorionic villus sampling.

Q. What’s the difference between deletion syndrome and duplication syndrome?

A deletion (loss) means chromosomal genetic material is missing; a duplication (gain) means there is extra genetic material. Even within the same BP4–BP5 range of 15q13.3, a deletion and a duplication are treated as entirely different conditions. Duplication syndrome tends to show a wider range of symptom presentations than deletion syndrome, and many people with it have no symptoms at all. Check your test report to see whether it specifies “deletion” or “duplication.”

Q. How is a definitive diagnosis reached?

A definitive diagnosis is reached through chromosomal microarray testing, which can detect small chromosomal deletions or duplications. Prenatally, this is done on cells collected via amniocentesis or chorionic villus sampling. After birth, it can be done from a blood draw with no miscarriage risk involved. Subtle changes that conventional microscope-based chromosome analysis can miss are picked up by this test.

Q. Is this caused by anything the parents did — their parenting or how the pregnancy was managed?

No, it is not. Roughly 75% of these deletions are inherited from one parent, and that parent often has no obvious symptoms — this is a result of incomplete penetrance, a feature of how this condition is inherited. The remaining cases arise as new (de novo) genetic changes. It has nothing to do with parenting style or how the pregnancy was managed; it is a genetic event that can happen to anyone. If this concerns you, genetic counseling is available to talk it through.

Q. How severe are the symptoms likely to be?

There is enormous individual variation in how symptoms present. Some people have prominent epilepsy or intellectual disability, while others show no noticeable symptoms at all — a feature known as incomplete penetrance. Rather than assuming an “average” case, it helps to look carefully at what’s actually happening for your own child or yourself, and build support around that.

Q. I’m not sure whether to have prenatal testing. What should I do?

Choosing to test and choosing not to are both meaningful, valid decisions for your family. Feeling torn is natural, so please don’t carry it alone. Genetic counseling lets you talk it through with a specialist, sorting out what a test can and can’t tell you and what your options are afterward. The process of reaching a decision you feel at peace with is, in itself, a way of engaging with your baby.