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Actin remodeling
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Adenosine degradation
Dynein motor activity
Immunoglobulin production
Microtubule polymerization
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This patient who presents with recurrent respiratory tract infections and dextrocardia (right-sided heart sounds) most likely has Kartagener syndrome. This disease is caused by a defect in dynein arm motor function. Cilia are cytoskeletal structures that are composed of a 9+2 arrangement of microtubules. These microtubules are linked by axonemal dynein, a molecular motor protein that causes bending of cilium by binding differentially to different tubules. Kartagener syndrome or immotile cilia disease is caused by a dynein arm defect and presents with infertility, recurrent infections, and situs inversus. Infertility is caused by immotile sperm (dysfunctional flagellar tail) or immobile cilia within the Fallopian tubes. Infections are caused by the inability to move mucus in the airway resulting in bronchiectasis. Finally, situs inversus (most prominently seen as dextrocardia) is caused by dysfunction of embryonic patterning cells that rely upon ciliary function to establish left/right asymmetry. Hoben et al. discuss the molecular mechanisms underlying primary ciliary dyskinesia. They find that mutations in proteins involved in the cytoplasmic assembly of dynein arms as well as dynein motor activity can result in this syndrome. Incorrect Answers: Answer 1: Actin remodeling is defective in Wiskott-Aldrich syndrome; however, this syndrome would present with thrombocytopenic purpura and eczema in addition to recurrent infections. Answer 2: Adenosine degradation is defective in patients with autosomal recessive severe combined immunodeficiency disorder; however, these patients would present with life-threatening infections including viral, bacterial, and fungal of all organ systems rather than only respiratory infections. Answer 4: Immunoglobulin production is defective in patients with Bruton agammaglobulinemia; however, this disease would present with absent/scant lymphoid tissues (tonsils/lymph nodes) in addition to recurrent infections starting at 6 months of age. Answer 5: Microtubule polymerization is defective in Chédiak–Higashi syndrome; however, this disease would present with partial albinism and peripheral neuropathy in addition to recurrent infections. Bullet Summary: Dynein motor dysfunction results in Kartagener syndrome that presents with infertility, situs inversus, and recurrent respiratory infections.
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