Jacobsen Syndrome

Jacobsen syndrome is a rare chromosomal disorder in which several genes on chromosome 11 are missing (deleted). This deletion happens at the end (terminus) of the long (q) arm of chromosome 11. Another name for the condition is 11q terminal deletion disorder.

Losing a smaller part of 11q means fewer genes are affected. So, people with smaller deletions tend to have milder symptoms than people with larger deletions. People with smaller deletions have partial Jacobsen syndrome or partial monosomy 11q. Partial monosomy means a part of one chromosome in a pair is deleted.

Jacobsen syndrome causes developmental delays, behavioral issues and distinctive facial features. Many children with the condition also have congenital heart defects. They also have an increased risk for a bleeding disorder called Paris-Trousseau syndrome.

There isn’t a cure for Jacobsen syndrome, and life expectancy varies.

Symptoms of Jacobsen syndrome

Jacobsen syndrome symptoms vary based on the location and size of the chromosomal deletion. Most people with the condition will experience developmental delays in their speech and motor skills. They may also have cognitive impairment and other learning disabilities.

Many children with Jacobsen syndrome have behavioral issues. These may include compulsive behavior and a short attention span. Many children have also been diagnosed with attention-deficit/hyperactivity disorder (ADHD). The condition is associated with an increased risk of autism spectrum disorders as well.

Children with Jacobsen syndrome have distinctive facial features. Jacobsen syndrome characteristics may include:

• A large head (macrocephaly)
• A pointed forehead caused by a skull abnormality called trigonocephaly
• Small, low-set ears
• Widely set eyes (hypertelorism)
• Droopy eyelids (ptosis)
• Skin folds covering the inner corner of their eyes (epicanthal folds)
• A wide nose bridge
• Downturned corners of their mouth
• A thin upper lip
• A small lower jaw

Other characteristics of Jacobsen syndrome may include:

• Congenital heart defects
• Feeding difficulties
• Growth delay before and after birth
• Short stature
• Frequent sinus and ear infections
• Abnormalities of their digestive system, kidneys and genitalia

Most people with Jacobsen syndrome also have a bleeding disorder called Paris-Trousseau syndrome. This condition affects your child’s platelets. Platelets are blood cells that are important for blood clotting. With Paris-Trousseau syndrome, your child has a lifelong risk of abnormal bleeding, and they may bruise easily.

Jacobsen syndrome causes

Jacobsen syndrome is a chromosomal disorder. Chromosomes are a part of your body that contain genetic material (genes). Genes tell your body how to develop and function. The human body normally has 22 numbered pairs of chromosomes, as well as a pair of sex chromosomes. Each of your chromosomes has a short (p) arm and a long (q) arm.

In some people, genes are missing (deleted) at the end of the long (q) arm of one chromosome 11, while the other chromosome 11 is usually intact. This causes Jacobsen syndrome. Larger deletions typically cause more severe symptoms to appear than smaller deletions. Depending on its size, the deleted area can contain from 170 to more than 340 genes. The genes in this area are responsible for the normal development of your heart, brain and facial features.

Is Jacobsen syndrome dominant or recessive?

Dominant or recessive refers to the way you receive (inherit) your genes from each biological parent.

But most cases of Jacobsen syndrome aren’t inherited. Instead, they result from a chromosomal deletion that occurs randomly. This random deletion happens after an error in cell division during fetal development. There’s nothing that a parent does to cause this deletion to happen, and nothing that can be done to prevent this from happening. People with Jacobsen syndrome usually don’t have a family history of the disorder. But they can pass the deletion on to their children.

In some cases, people with Jacobsen syndrome inherit the deletion from an unaffected parent. This can occur when a parent carries a chromosomal rearrangement called a balanced translocation. In the case of Jacobsen syndrome, that means a segment from chromosome 11 has swapped positions with a segment from another chromosome. No genetic material is lost, and the parent doesn’t show any symptoms. But the chromosomes can become unbalanced as they’re passed on.

Risk factors for Jacobsen syndrome

Jacobsen syndrome is a genetic condition that can affect anyone. Some research has found that the disorder affects more female babies.

How doctors diagnose Jacobsen syndrome

Your healthcare provider may be able to diagnose Jacobsen syndrome during your pregnancy. If prenatal ultrasound scans indicate a concern, your provider may recommend additional testing. Common prenatal genetic screening tests include:

• Non-invasive prenatal testing (NIPT). A provider will look for abnormal chromosome numbers in small amounts of fetal DNA found in your blood.
• Chorionic villus sampling (CVS). A provider uses a needle to remove a sample of cells from the placenta.
• Amniocentesis. A provider uses a needle to remove a sample of amniotic fluid from the amniotic sac.

After birth, your baby’s healthcare provider can use genetic testing to diagnose Jacobsen syndrome. During genetic testing, a provider examines a sample of your baby’s blood under a microscope. They stain the chromosomes in the sample, which makes them look kind of like a barcode. The provider can see broken chromosomes and deleted genes. They can normally see the broken chromosome 11. But further genetic testing is usually required to accurately determine the breakage point.

Additional testing may include microarray comparative genomic hybridization (array CGH). Subtle changes in the chromosomes that are too small to see using a microscope may cause Jacobsen syndrome. So, a provider may use array CGH. Array CGH shows the deletions of microscopic amounts of DNA throughout your baby’s chromosomes. Array CGH can detect and identify duplicated, disrupted or missing DNA.

How is Jacobsen syndrome treated?

There’s no cure for Jacobsen syndrome. Treatment focuses on:

• Managing your child’s symptoms
• Helping them reach their developmental milestones
• Preventing health complications

For babies with feeding issues, providers may recommend a gastrostomy tube (G-tube). The tube goes directly into your baby’s stomach to provide food. A surgical operation called a fundoplication can help correct an issue with the valve at the bottom of their esophagus.

Your child may need other surgeries as well. This may include surgery to correct skull and face (craniofacial) issues like trigonocephaly. They may have surgery to fix issues with their vision or eyes. Other surgeries may be needed to correct skeletal, cardiac and other defects.

Your child’s provider may treat the complications of some heart defects with certain medications. For instance, they may prescribe antiarrhythmics. These are drugs that can help prevent or correct abnormal heart rhythms. They may also suggest diuretics, which are drugs that can help get rid of extra fluid from their body.

Your child’s provider may correct eye abnormalities with corrective glasses, contact lenses or surgery.

Providers may treat the effects of Paris-Trousseau syndrome with blood or platelet transfusions. Your child may also receive a drug called desmopressin that helps their blood clot.

Your child will likely eventually reach their developmental milestones. But early intervention can ensure that they’ll reach their highest potential. Your child’s provider may recommend:

• Special remedial education
• Physical therapy
• Speech therapy

How can I prevent Jacobsen syndrome?

You can’t prevent Jacobsen syndrome because it’s a genetic condition. If you’re pregnant or planning to become pregnant, consider asking your provider about genetic counseling. A genetic counselor can help you understand your risk of having a child with Jacobsen syndrome.

What can I expect if my child has Jacobsen syndrome?

The life expectancy of people with Jacobsen syndrome varies based on the severity of their symptoms. Due to serious heart conditions and blood clotting issues, 20% of babies with Jacobsen syndrome die before the age of 2.

But many children with Jacobsen syndrome have lived into adulthood. Adults with the condition can live happy, fulfilling lives with varying levels of independence.