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TBX3, TBX5, and the Ulnar-Mammary and Holt-Oram Syndromes 

TBX3, TBX5, and the Ulnar-Mammary and Holt-Oram Syndromes
TBX3, TBX5, and the Ulnar-Mammary and Holt-Oram Syndromes

Michael J. Bamshad

and Lynn B. Jorde

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date: 07 March 2021

Ulnar–mammary syndrome (UMS) and Holt–Oram syndrome (HOS) are rare, autosomal dominant, multiple malformation disorders. UMS is characterized by apocrine abnormalities including breast defects and malformations of the posterior elements of the upper limb. In contrast, HOS is typified by heart malformations, most commonly an atrial septal defect (ASD) or ventricular septal defect (VSD), conduction abnormalities, and defects of the anterior elements of the upper limb. UMS and HOS are caused by mutations in TBX3 and TBX5, respectively, two members of the T-box gene family linked together on chromosome 12q24. The long-term care of patients with UMS or HOS can be challenging, but in general, most patients do well. In the heart, TBX5 plays an important role in formation of the septa, chambers, and conduction system. In the limb, Tbx5 appears to activate fibroblast growth factor-10 (Fgf10) to initiate forelimb bud outgrowth. Tbx3 plays multiple roles in a variety of developmental processes including maintenance of stem cells, cell-fate determination, and formation of the heart, mammary glands, and limbs. Mice haploinsufficient for Tbx3 or lacking functional Tbx5 exhibit malformations that recapitulate many of the defects observed in UMS and HOS, respectively.

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