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Boomerang dysplasia

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Description

Boomerang dysplasia is a disorder that affects the development of bones throughout the body. Affected individuals are born with inward- and upward-turning feet (clubfeet) and dislocations of the hips, knees, and elbows. Bones in the spine, rib cage, pelvis, and limbs may be underdeveloped or in some cases absent. As a result of the limb bone abnormalities, individuals with this condition have very short arms and legs. Pronounced bowing of the upper leg bones (femurs) gives them a "boomerang" shape.

Some individuals with boomerang dysplasia have a sac-like protrusion of the brain (encephalocele). They may also have an opening in the wall of the abdomen (an omphalocele) that allows the abdominal organs to protrude through the navel. Affected individuals typically have a distinctive nose that is broad with very small nostrils and an underdeveloped partition between the nostrils (septum).

Individuals with boomerang dysplasia typically have an underdeveloped rib cage that affects the development and functioning of the lungs. As a result, affected individuals are usually stillborn or die shortly after birth from respiratory failure.

Frequency

Boomerang dysplasia is a rare disorder; its exact prevalence is unknown. Approximately 10 affected individuals have been identified.

Causes

Mutations in the FLNB gene cause boomerang dysplasia. The FLNB gene provides instructions for making a protein called filamin B. This protein helps build the network of protein filaments (cytoskeleton) that gives structure to cells and allows them to change shape and move. Filamin B attaches (binds) to another protein called actin and helps the actin to form the branching network of filaments that makes up the cytoskeleton. It also links actin to many other proteins to perform various functions within the cell, including the cell signaling that helps determine how the cytoskeleton will change as tissues grow and take shape during development.

Filamin B is especially important in the development of the skeleton before birth. It is active (expressed) in the cell membranes of cartilage-forming cells (chondrocytes). Cartilage is a tough, flexible tissue that makes up much of the skeleton during early development. Most cartilage is later converted to bone (a process called ossification), except for the cartilage that continues to cover and protect the ends of bones and is present in the nose, airways (trachea and bronchi), and external ears. Filamin B appears to be important for normal cell growth and division (proliferation) and maturation (differentiation) of chondrocytes and for the ossification of cartilage.

FLNB gene mutations that cause boomerang dysplasia change single protein building blocks (amino acids) in the filamin B protein or delete a small section of the protein sequence, resulting in an abnormal protein. This abnormal protein appears to have a new, atypical function that interferes with the proliferation or differentiation of chondrocytes, impairing ossification and leading to the signs and symptoms of boomerang dysplasia.

Inheritance

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Almost all cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

Other Names for This Condition

  • Piepkorn dysplasia

Additional Information & Resources

Genetic Testing Information

Genetic and Rare Diseases Information Center

Patient Support and Advocacy Resources

Catalog of Genes and Diseases from OMIM

Scientific Articles on PubMed

References

  • Bicknell LS, Morgan T, BonafĂ© L, Wessels MW, Bialer MG, Willems PJ, Cohn DH, Krakow D, Robertson SP. Mutations in FLNB cause boomerang dysplasia. J Med Genet. 2005 Jul;42(7):e43. Citation on PubMed or Free article on PubMed Central
  • Krakow D, Robertson SP, King LM, Morgan T, Sebald ET, Bertolotto C, Wachsmann-Hogiu S, Acuna D, Shapiro SS, Takafuta T, Aftimos S, Kim CA, Firth H, Steiner CE, Cormier-Daire V, Superti-Furga A, Bonafe L, Graham JM Jr, Grix A, Bacino CA, Allanson J, Bialer MG, Lachman RS, Rimoin DL, Cohn DH. Mutations in the gene encoding filamin B disrupt vertebral segmentation, joint formation and skeletogenesis. Nat Genet. 2004 Apr;36(4):405-10. Epub 2004 Feb 29. Citation on PubMed
  • Sawyer GM, Clark AR, Robertson SP, Sutherland-Smith AJ. Disease-associated substitutions in the filamin B actin binding domain confer enhanced actin binding affinity in the absence of major structural disturbance: Insights from the crystal structures of filamin B actin binding domains. J Mol Biol. 2009 Jul 31;390(5):1030-47. doi: 10.1016/j.jmb.2009.06.009. Epub 2009 Jun 6. Citation on PubMed
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