Bardet-Biedl Syndrome

Diagnosis and Testing

How do I get tested for Bardet-Biedl Syndrome?

Diagnosis is generally made in late childhood or early adulthood. Generally, Bardet-Biedl syndrome is first suspected when vision worsens around 7-8 years of age. When suspicious that a child has Bardet-Biedl syndrome, talking to a doctor about a referral to ophthalmology (eye doctor) is strongly recommended. A test that ophthalmologists can use to check for vision loss is done with an electroretinogram (ERG); it should be noted that significant changes in vision are usually not seen in people with Bardet-Biedl syndrome before five years of age.

References
  • Reference: Forsythe, E. & Beales, P.L. (2012). Bardet-Biedl syndrome. European Journal of Human Genetics 21: 8-13.
  • http://www.nature.com/ejhg/journal/v21/n1/full/ejhg2012115a.html
  • http://www.ncbi.nlm.nih.gov/books/NBK1363/
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More Diagnosis and Testing Content

Is there newborn testing for Bardet-Biedl Syndrome?

Is there more than one type of test for Bardet-Biedl Syndrome?

Who else in my family should I test for Bardet-Biedl Syndrome?

How is Bardet-Biedl syndrome diagnosed?

Does it matter if you test blood versus saliva versus a biopsy for Bardet-Biedl Syndrome?

Is there newborn testing for Bardet-Biedl Syndrome?

Screening with a second-trimester ultrasound can reveal the anomalies typical of Bardet-Biedl syndrome, such as polydactyly and renal abnormalities. However, ultrasound cannot definitively rule out a diagnosis, as not all Bardet-Biedl babies will have these findings. If the familial mutations are already known, prenatal genetic testing may be performed through chorionic villi sampling (CVS) or an amniocentesis.

References
  • http://www.ncbi.nlm.nih.gov/books/NBK1363/
Is there more than one type of test for Bardet-Biedl Syndrome?

For a clinical diagnosis a doctor may order a kidney ultrasound to check for any malformations. For a vision test, a doctor (or ophthalmologist) may order an electroretinogram (ERG) to measure the response of eyes to light. When pursuing genetic testing, sequence analysis detects the majority of genetic changes and a genetic panel (looking at multiple genes associated with Bardet-Biedl syndrome, not just BBS1) will likely be ordered. A doctor may order targeted testing when a patient knows of a family member with a mutation associated with Bardet-Biedl syndrome in order to examine the specific gene mutated in the relative.

References
  • http://www.ncbi.nlm.nih.gov/books/NBK1363/
  • http://www.ncbi.nlm.nih.gov/gtr/tests/?term=C0752166[DISCUI]&condition=C0752166&compare_labs=1
Who else in my family should I test for Bardet-Biedl Syndrome?

Carriers for Bardet-Biedl syndrome (those with one mutation but are unaffected by the condition) should ask parents and siblings to consider getting tested. Those with children or who are planning to have children should also ask their partners about testing for a mutation linked to Bardet-Biedl syndrome. If two would-be parents are carriers, each pregnancy carries a 25% risk for Bardet-Biedl syndrome.

Those with Bardet-Biedl syndrome should suggest that their parents and siblings get tested; their parents are most likely carriers for Bardet-Biedl syndrome, which means further that their siblings have a 50% chance of also being carriers. Someone with Bardet-Biedl syndrome with children or planning to have children should ask her partner about testing: if her partner is not a carrier, each child would be a carrier; if her partner is a carrier for Bardet-Biedl syndrome, each child would have a 50% risk of being a carrier and a 50% risk of inheriting Bardet-Biedl syndrome; if her partner also has Bardet-Biedl syndrome, each child would inherit Bardet-Biedl syndrome. Importantly, though, carrier testing cannot identify all mutations that case Bardet-Biedl syndrome.

References
  • http://www.ncbi.nlm.nih.gov/books/NBK1363/
How is Bardet-Biedl syndrome diagnosed?

Bardet-Biedl syndrome is typically clinically diagnosed in childhood by identifying its characteristic presentations (ex. extra fingers and/or toes, obesity, vision problems). An ophthalmologist may diagnose it with an electroretinogram (ERG), measuring the eyes’ response to light.

For a clinical diagnosis a person either needs to present with 4 primary features or 3 primary and 2 secondary features.

Primary features

  • Rod-cone dystrophy (eye finding)
  • Extra fingers and/or toes
  • Obesity
  • Kidney anomalies
  • Learning difficulties

Secondary features

  • Speech delay
  • Developmental delay
  • Diabetes mellitus
  • Dental (teeth) anomalies
  • Congenital (from birth) heart disease
  • Clumsy, poor coordination (ataxia)
  • Short and/or fused fingers and/or toes
  • Lack of smell
References
  • http://rarediseases.org/rare-diseases/bardet-biedl-syndrome/
  • Reference: Forsythe, E. & Beales, P.L. (2012). Bardet-Biedl syndrome. European Journal of Human Genetics 21: 8-13.
  • http://www.nature.com/ejhg/journal/v21/n1/full/ejhg2012115a.html
Does it matter if you test blood versus saliva versus a biopsy for Bardet-Biedl Syndrome?

The lab running the test will determine the sample type; Bardet-Biedl syndrome should not affect which sample type (blood or saliva) will work best. A biopsy should not be needed for a genetic test for Bardet-Biedl syndrome.

References
  • http://www.ncbi.nlm.nih.gov/books/NBK1363/
  • http://dnatesting.uchicago.edu/tests/bardet-biedl-syndrome-sequencing-panel

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