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Diseases

Genetic and Rare Diseases Information Center (GARD)

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Barth syndrome


Other Names for this Disease
  • 3-methylglutaconic aciduria type II
  • BTHS
  • Cardioskeletal myopathy with neutropenia and abnormal mitochondria
  • MGA type II
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Inheritance


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How is Barth syndrome inherited?

The malfunctioning gene that causes Barth syndrome is located on the X chromosome, and Barth syndrome is inherited in an X-linked recessive manner. Chromosomes, inside the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes - 23 inherited from each parent. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome, and females have two X chromosomes.[1]

X-linked recessive genetic disorders are conditions caused by an abnormal gene on the X chromosome. Females have two X chromosomes but one of the X chromosomes is "turned off" and all of the genes on that chromosome are inactivated. Females who have a disease gene present on one of their X chromosomes are considered carriers for that disorder. Carrier females usually do not display symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is "turned off", and they have another X chromosome with a working copy of the gene. A male has only one X chromosome. Therefore, if he inherits an X chromosome that contains a non-working gene, he will develop the disease that is associated with that gene.[1] This is why Barth syndrome occurs exclusively in males.

Males with X-linked disorders pass the disease gene to all of their daughters, who will be carriers. A male cannot pass an X-linked gene to his sons, because males always pass their Y chromosome instead of their X chromosome to male offspring (which is what makes the offspring male).[1] A female carrier of an X-linked disorder has two X chromosomes and will always pass one of them onto her offspring (whether it is male or female). Female carriers of and X-linked disorder have a 25 percent chance with each pregnancy to have a carrier daughter like themselves, a 25 percent chance to have a non-carrier daughter, a 25 percent chance to have a son affected with the disease, and a 25 percent chance to have an unaffected son. In some instances, the mother of an affected male may not be a carrier for Barth syndrome and there is no apparent family history of the disease. In such cases, the disorder appears to result from a new mutation of the gene on the X chromosome of the affected individual that occurred randomly for unknown reasons (sporadically).[1]
Last updated: 6/3/2011

References
  1. Barth Syndrome. NORD. September 17, 2007; http://www.rarediseases.org/rare-disease-information/rare-diseases/byID/1116/viewAbstract. Accessed 6/3/2011.