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Diseases

Genetic and Rare Diseases Information Center (GARD)

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Down syndrome

*


* Not a rare disease
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Other Names for this Disease
  • Down's syndrome
  • Trisomy 21
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Your Question

My daughter is 9 months old and has Down syndrome. She also has a strong, fish-like odor coming from the mouth. Is it possible that she could also have trimethylaminuria? How might a person be tested for this condition?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

Is it possible for an individual to have both Down syndrome and trimethylaminuria?

It is technically possible for an individual to have both Down syndrome and trimethylaminuria. The gene that is typically mutated in an individual with trimethylaminuria (FMO3) is located on chromosome 1.[1] Trimethylaminuria is usually inherited in an autosomal recessive manner, which means that two mutated FMO3 genes are usually needed for a person to have symptoms. Each parent of an individual with an autosomal recessive condition, such as trimethylaminuria, carries one copy of the mutated gene and are referred to as carriers. Since this condition usually requires two altered genes to cause symptoms, typically neither parent of an individual with trimethylaminuria has any symptoms. Sometimes, however, carriers of an FMO3 mutation may have mild symptoms of trimethylaminuria or have temporary episodes of fish-like odor.[2]

Most cases of Down syndrome result from trisomy 21, which means each cell in the body has three copies of chromosome 21 instead of the usual two copies. The extra genetic material disrupts the normal course of development, causing the characteristic features of Down syndrome. A small percentage of people with Down syndrome have an extra copy of chromosome 21 in only some of the body's cells (mosaic Down syndrome), and others may have it because part of chromosome 21 becomes attached (translocated) to another chromosome during the formation of reproductive cells (eggs and sperm) or very early in fetal development (translocation Down syndrome).[3]

The genetic changes that cause trimethylaminuria (on chromosome 1) are very different from those that cause Down syndrome (and involve chromosome 21) and the two conditions are completely unrelated. Although it is uncommon, it is possible for an individual to have any form of Down syndrome, as well as an autosomal recessive condition such as trimethylaminuria.
Last updated: 12/22/2010

Is testing available for trimethylaminuria?

Yes. Trimethylaminuria can be diagnosed through a urine test that measures the amount of trimethylamine in the urine. If an individual is on a non-restricted diet, urine testing should be performed on two separate occasions.

 

Carrier testing is also available for trimethylaminuria. This test is called either a 'TMA challenge' or a 'TMA load' test. It involves giving an individual a 600mg capsule of trimethylamine. Then the amount of trimethylamine that is not broken down and excreted in the urine is measured. If an individual is a carrier, the amount of trimethylamine that is not broken down is 20-30% of total trimethylamine excreted. For people who are not carriers, the amount of trimethylamine that is not broken down is less than 13%.[4]

The laboratories listed below provide clinical diagnostic testing for elevated levels of trimethylamine in the urine. The Information Center provides the names of these centers for informational purposes only, not as an endorsement of the institutions' products or services. Please note that some laboratories do not accept direct contact from patients. Therefore, we recommend that you work with a medical or genetics professional to contact these laboratories for further information. 

Arkansas Children's Hospital
Metabolic Laboratory
Phone: (501) 364-1300
Web site: http://www.archildrens.org/documents/TMAinfoLab.pdf

Monell Chemical Senses Center
University of Pennsylvania
Phone: 267-519-4700
Contact: George Preti, PhD 
E-mail: preti@monell.org  
Web site: http://www.monell.org/contact_us/tmau/
For more information, patients can send an e-mail to: bodyodorinfo@monell.org 

The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.
Last updated: 1/27/2014

References