Jacobsen Syndrome Health Article

Diagnosis

Most individuals with Jacobsen syndrome are diagnosed after birth. The diagnosis is usually made through a blood test called chromosome analysis in an infant or child who has mental retardation and a typical facial appearance. The karyotype will show a deletion or rearrangement of the longer segment, known as the q arm, of one copy of chromosome 11. Jacobsen syndrome can be diagnosed before birth. There have been reports of prenatal diagnosis through amniocentesis after an ultrasound demonstrated one or more fetal abnormalities. Another technique, known as FISH (fluorescent in-situ hybridization), may be used to further define the chromosome 11q deletion breakpoints; this laboratory test is being done on a research basis to identify the disease-causing genes in the Jacobsen syndrome critical region.

Treatment and management

There is no cure for Jacobsen syndrome nor is there a therapy that can replace the missing genes from the deleted segment of chromosome 11. In addition to routine pediatric exams, there are management strategies and treatments that aim to prevent or minimize some of the serious health consequences associated with Jacobsen syndrome.

At the time of diagnosis a series of evaluations should be undertaken in order to appropriately guide medical management. Pediatric specialists in genetics, cardiology, orthopedics, ophthalmology, and neurology should be consulted, especially since some problems can be treated if caught early. Important tests may include a karyotype, a cardiac echocardiogram, a renal sonogram, a platelet count, a blood count, a brain imaging study, hearing and vision screenings, and a dental exam.

A neurodevelopmental evaluation should be initiated in infancy or at the time of diagnosis with implementation of age-appropriate early intervention services such as speech therapy, occupational therapy, and physical therapy. An ear, nose, and throat specialist (ENT) may be needed to treat problems such as otitis media. Craniofacial and neurosurgery consults may be indicated if trigonocephaly or other forms of craniosynostosis are present.

Some children may require a gastroenterology specialist to evaluate problems such as failure to thrive, chronic constipation, and/or severe gastroesophageal reflux, some or all of which may require surgical intervention. Boys with Jacobsen syndrome should be examined for undescended testes, a problem found in half of males and one that often requires surgery.

Prognosis

Approximately 25% of affected children die before two years of age mainly from cardiac defects, a tendency to bleed, or infection. Except for respiratory infections, the remainder of children are generally healthy. Most individuals described here are children or adolescents. Little is known about the course of this syndrome in adulthood, and the life expectancy for those who live beyond age two is unknown.

BOOKS

Jones, Kenneth Lyons. Smith's Recognizable Patterns of Human Malformation. Philadelphia: W.B. Saunders Company, 1997.

PERIODICALS

Jones, Christopher, et al. "Co-localisation of CCG repeats and chromosome deletion breakpoints in Jacobsen syndrome: evidence for a common mechanism of chromosome breakage." Human Molecular Genetics 9, no. 8: 1201–08.

McClelland, S. M., et al. "Nuchal thickening in Jacobsen syndrome." Ultrasound in Obstetrics and Gynecology 12 (1998): 280–82.

Ono, J., et al. "Partial deletion of the long arm of chromosome 11: ten Japanese children." Clinical Genetics 50 (1996): 474–78.

Penny, Laura A., et al. "Clinical and Molecular Characterization of Patients with Distal 11q Deletions." American Journal of Human Genetics 56 (1995): 676–83.

Pivnick, E. K., et al. "Jacobsen syndrome: report of a patient with severe eye anomalies, growth hormone deficiency, and hypothyroidism associated with deletion 11(q23q25) and review of 52 cases." Journal of Medical Genetics 33 (1996): 772–78.

Tunnacliffe, Alan, et al. "Localization of Jacobsen syndrome breakpoints on a 40-Mb physical map of distal chromosome 11q." Genome Research 9 (1999): 44–52.

ORGANIZATIONS

European Chromosome 11q Network. <http://www.11q.org>.

OTHER

11q Research and Resource Home Page. <http://www.11q.net>.

The Fragile WEB Site. <http://web.ukonline.co.uk>.

Dawn Cardeiro, MS, CGC