Jacobsen syndrome, also known as 11q terminal deletion disorder, is a rare genetic condition that is present from birth. To understand this, it is essential to know that our body’s genetic blueprint is organized into 23 pairs of chromosomes. In Jacobsen syndrome, a small piece of genetic material is missing (deleted) from the end of the long (q) arm of chromosome 11.

It is helpful to use an analogy. Think of your entire set of chromosomes as a multi-volume encyclopedia of instruction manuals for building and running a human body. Each chromosome is a single volume. Each page within that volume is a gene, containing a specific instruction. In Jacobsen syndrome, it is as if the very last chapter of Volume 11 has been accidentally torn out. Because this “lost chapter” contained many different pages (genes) with a variety of important instructions, for building parts of the heart, developing the face, forming blood platelets, and guiding brain development, the loss of this entire section leads to the wide range of health and developmental issues seen in the syndrome.

Because the number and size of missing genes can vary, the severity and range of symptoms also differ widely between individuals.

In my experience, families often come in with a cluster of unexplained symptoms, from heart defects to learning delays, and the diagnosis only becomes clear after genetic testing. It’s a condition that reveals itself gradually through developmental and medical patterns.

Jacobsen syndrome is caused by a deletion of genetic material on the long arm (q arm) of chromosome 11, usually near the end.  This is not a single gene mutation, but a larger-scale chromosomal error. The deleted segment can contain anywhere from about 5 million to 16 million DNA base pairs, encompassing a large number of genes.

While many genes are lost in this deletion, scientists have identified a few key genes whose absence is linked to the most significant features of the syndrome. For example, the loss of a gene called FLI1 is strongly associated with the characteristic bleeding disorder, Paris-Trousseau syndrome, that is a hallmark of the condition (NORD, 2023). The loss of other genes in the region contributes to the potential for heart defects, developmental delays, and other physical features. The loss of this genetic material occurs during cell division, but why this specific chromosomal error occurs is not known.

I’ve seen parents struggle with guilt over a diagnosis like this, but it’s important to emphasize that most cases are not inherited. This is usually a spontaneous chromosomal error, not something anyone could have prevented.

The way Jacobsen syndrome arises is a critical point of understanding for parents, as it is almost never something that is passed down in a predictable way.

A Sporadic, Random Event

In approximately 95% of cases, the chromosomal deletion that causes Jacobsen syndrome is a sporadic or de novo event. This means that the error, the breaking off of the end of chromosome 11, occurs by complete chance during the formation of the reproductive cells (egg or sperm) in a healthy parent, or during the earliest stages of fetal development. It is not caused by anything the parents did or did not do before or during the pregnancy. In these cases, the parents have normal chromosomes, and the risk of them having another child with Jacobsen syndrome is extremely low.

Rare Inherited Cases

In a very small percentage of cases (about 5%), a child can inherit the deletion from an unaffected parent who carries a “balanced translocation.” In a balanced translocation, a piece of chromosome 11 has broken off and reattached to another chromosome, so no genetic material is lost, and the parent is healthy. However, when this parent creates reproductive cells, there is a risk of passing on an “unbalanced” set of chromosomes, one that is missing that final piece of chromosome 11. Genetic counseling is very important for families where an inherited translocation is identified.

In the clinic, I’ve often encountered parents who only received the diagnosis after years of chasing answers. The symptoms can be subtle at first, so unless there’s a major birth defect, it often takes a full genetic panel to uncover the underlying cause.

Symptoms of Jacobsen syndrome can vary depending on the size of the chromosome deletion. No two individuals will be exactly alike, and the severity can vary greatly.

The most common features affect several different body systems:

Distinctive Craniofacial Features

Many children with Jacobsen syndrome share a recognizable set of facial features. These can include:

• Trigonocephaly: A pointed or triangular-shaped forehead.
• Hypertelorism: Widely spaced eyes.
• Ptosis: Drooping of the upper eyelids.
• Downward-slanting eyes, small and low-set ears, broad nasal bridge.

Bleeding Disorder (Paris-Trousseau Syndrome)

A hallmark and medically significant feature of Jacobsen syndrome is a lifelong bleeding disorder known as Paris-Trousseau syndrome. This is characterized by:

• Thrombocytopenia: A low blood platelet count, the cell fragments responsible for forming blood clots.
• Abnormal Platelet Function: The platelets that are present do not function correctly.
• This combination leads to a risk of easy bruising and abnormal or prolonged bleeding, which requires careful management, especially during any surgery, dental work, or after an injury.

Growth and Development

• Slow Growth: Most children with Jacobsen syndrome have slow growth, both before birth (intrauterine growth restriction) and after, leading to short stature.
• Microcephaly: A smaller than average head size is common.
• Developmental Delays: Most individuals have some degree of developmental delay and intellectual disability, which can range from mild to moderate. Delays in reaching motor milestones (like sitting and walking) and speech and language delays are very common.
• Behavioral Issues: Many children and adults with Jacobsen syndrome exhibit behavioral characteristics that can include compulsive behaviors, short attention span, and features of attention-deficit/hyperactivity disorder (ADHD) or autism spectrum disorder.

Congenital Heart Defects

A very high percentage of individuals with Jacobsen syndrome over 90% are born with a structural heart defect. The problems most often affect the left side of the heart. Common defects include hypoplastic left heart syndrome, aortic coarctation, and ventricular septal defects (VSD).

Other Potential Issues

• Abnormalities of the hands and feet, such as hammertoes or clinodactyly (curved fingers).
• Gastrointestinal problems, such as pyloric stenosis (a narrowing of the stomach outlet).
• Kidney problems.
• Hearing and vision problems.
• Immune system deficiencies.

What stands out to me is how the condition rarely affects just one system. You often see a child with cardiac issues, developmental delays, and easy bruising, all pointing to a bigger underlying genetic issue like Jacobsen.

A diagnosis of Jacobsen syndrome may be suspected before birth if a routine prenatal ultrasound shows growth restriction or a congenital heart defect. In other cases, it is suspected at birth or in early infancy when a doctor recognizes the combination of characteristic facial features, slow growth, and signs of a bleeding disorder.

The diagnosis is confirmed with chromosome analysis using a blood sample.

• Karyotyping: This is a classic laboratory technique where a picture of the baby’s chromosomes is created to be examined under a microscope. In many cases, the large deletion at the end of chromosome 11 can be seen directly.
• Fluorescence In Situ Hybridization (FISH) or Chromosomal Microarray: These are more advanced and sensitive genetic tests that can more precisely identify the presence and size of the deletion, even if it is too small to be seen on a standard karyotype.

A Comprehensive Evaluation

Once Jacobsen syndrome is diagnosed, a comprehensive evaluation is essential. This workup must include:

• A complete echocardiogram to diagnose any heart defects.
• A hematology consultation to evaluate and manage the bleeding disorder.
• A renal ultrasound to check the kidneys.
• A thorough eye exam and hearing test.
• A developmental assessment.

The diagnosis is usually confirmed with microarray testing, but the clues often come from a pattern, heart murmur, developmental delay, and frequent nosebleeds are a trio I’ve learned not to ignore.

There is no cure for Jacobsen syndrome, but supportive care can greatly improve quality of life. This requires a coordinated, multidisciplinary team of specialists. This team may include a pediatrician, clinical geneticist, cardiologist, hematologist, endocrinologist, neurologist, ophthalmologist, and physical, occupational, and speech therapists.

The key management strategies include:

• Hematology and Bleeding Precautions: This is a critical aspect of lifelong care. Individuals require regular monitoring of their platelet counts by a hematologist. They must be given platelet transfusions before any planned surgery or dental procedure. It is also vital that they avoid medications that disrupt platelet function, such as aspirin and ibuprofen.
• Cardiac Management: The treatment of any congenital heart defect is a priority. This often requires medical management or open-heart surgery in infancy. Lifelong follow-up with a cardiologist is essential.
• Developmental Support: This is the cornerstone of helping a child reach their potential. Early and intensive intervention with physical therapy, occupational therapy, and speech therapy is crucial to address motor and language delays. Most children will require a specialized education plan (IEP) at school to support their unique learning needs.
• Growth Monitoring: An endocrinologist will monitor the child’s growth. In some cases, growth hormone therapy may be considered, although its effectiveness can vary.
• Routine Screenings: Lifelong, regular check-ups for vision, hearing, and kidney function are necessary to monitor for any developing issues.

In my experience, early intervention is the game changer. Kids who get support with speech, coordination, and behavior early on often surprise their families, and even their doctors, with how much they can achieve.

Jacobsen syndrome is a rare and complex chromosomal disorder that presents a family with a journey of significant medical and developmental challenges. The condition’s wide spectrum of features, particularly its impact on the heart, blood platelets, and cognitive development, requires care from a dedicated and coordinated team of specialists. While the diagnosis can be daunting, it is important for families to know that it is almost always a random event and not their fault. Though there is no cure, a proactive and comprehensive management plan focused on treating the associated health problems and providing robust developmental support can make a world of difference. What I often tell families is this: while Jacobsen syndrome may sound overwhelming, each child is unique, and with a caring, informed team around them, they can thrive in their own way.

National Institutes of Health, Genetic and Rare Diseases Information Center (GARD). (2023). Jacobsen syndrome. Retrieved from https://rarediseases.info.nih.gov/diseases/6811/jacobsen-syndrome

National Organization for Rare Disorders (NORD). (2023). Jacobsen Syndrome. Retrieved from https://rarediseases.org/rare-diseases/jacobsen-syndrome/

MedlinePlus Genetics. (n.d.). Jacobsen syndrome. U.S. National Library of Medicine. Retrieved July 2, 2025, from https://medlineplus.gov/genetics/condition/jacobsen-syndrome/