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Query: UMLS:C0265264 (HOS)
 1,119 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Holt-Oram syndrome is one of the autosomal dominant human "heart-hand" disorders, with a combination of upper limb malformations and cardiac defects. Holt-Oram syndrome is caused by mutations in the TBX5 gene, a member of a large family of T-box transcription factors that play important roles in cell-type specification and morphogenesis. In a screen for mutations affecting zebrafish cardiac function, we isolated the recessive lethal mutant heartstrings, which lacks pectoral fins and exhibits severe cardiac dysfunction, beginning with a slow heart rate and progressing to a stretched, non-functional heart. We mapped and cloned the heartstrings mutation and find it to encode the zebrafish ortholog of the TBX5 gene. The heartstrings mutation causes premature termination at amino acid 316. Homozygous mutant embryos never develop pectoral fin buds and do not express several markers of early fin differentiation. The total absence of any fin bud differentiation distinguishes heartstrings from most other mutations that affect zebrafish fin development, suggesting that Tbx5 functions very early in the pectoral fin induction pathway. Moderate reduction of Tbx5 by morpholino causes fin malformations, revealing an additional early requirement for Tbx5 in coordinating the axes of fin outgrowth. The heart of heartstrings mutant embryos appears to form and function normally through the early heart tube stage, manifesting only a slight bradycardia compared with wild-type siblings. However, the heart fails to loop and then progressively deteriorates, a process affecting the ventricle as well as the atrium. Relative to mammals, fish require lower levels of Tbx5 to produce malformed appendages and display whole-heart rather than atrial-predominant cardiac defects. However, the syndromic deficiencies of tbx5 mutation are remarkably well retained between fish and mammals.
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PMID:The heartstrings mutation in zebrafish causes heart/fin Tbx5 deficiency syndrome. 1222 19

T box (Tbx) genes are a large family of transcription regulators that play critical roles in invertebrate and vertebrate development. Mutations in Tbx5 gene have been found to cause Holt-Oram syndrome (HOS) in humans. Partial dysfunction of TBX5 in mouse also causes HOS phenotype. Little is known about its molecular and cellular mechanism. Here, we report that ectopic expression of TBX5 inhibited colony formation, induced apoptosis, and decreased the growth rate of cells. The two point mutations in T domain and a truncated mutation in C-terminal found in human HOS patients produced TBX5 mutant proteins with a significantly reduction of colony suppression activity. Deletion of the DNA-binding domain, however, nearly completely abrogated its ability to suppress colony formation. These results reveal TBX5 as a new regulator of apoptosis and cell growth, suggesting a possible mechanism for Holt-Oram syndrome, and a potential reagent for controlling tumor growth.
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PMID:Induction of apoptosis and inhibition of cell growth by developmental regulator hTBX5. 1223

Okihiro syndrome refers to the association of forearm malformations with Duane syndrome of eye retraction. Based on the reported literature experience, clinical diagnosis of the syndrome can be elusive, owing to the variable presentation in families reported. Specifically, there is overlap of clinical features with other conditions, most notably Holt-Oram syndrome, a condition resulting from mutation of the TBX5 locus and Townes-Brocks syndrome, known to be caused by mutations in the SALL1 gene. Arising from our observation of several malformations in Okihiro syndrome patients which are also described in Townes-Brocks syndrome, we postulated that Okihiro syndrome might result from mutation of another member of the human SALL gene family. We have characterized the human SALL4 gene on chromosome 20q13.13-q13.2. Moreover, we have identified literature reports of forelimb malformations in patients with cytogenetically identifiable abnormalities of this region. We here present evidence in 5 of 8 affected families that mutation at this locus results in the Okihiro syndrome phenotype.
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PMID:Okihiro syndrome is caused by SALL4 mutations. 1239 9

Holt-Oram syndrome is an autosomal-dominant condition characterized by congenital cardiac and forelimb anomalies. It is caused by mutations of the TBX5 gene, a member of the T-box family that encodes a transcription factor. Molecular studies have demonstrated that mutations predicted to create null alleles cause substantial abnormalities in both the limbs and heart, and that missense mutations of TBX5 can produce distinct phenotypes. One class of missense mutations causes significant cardiac malformations but only minor skeletal abnormalities; others might cause extensive upper limb malformations but less significant cardiac abnormalities. Intrafamilial variations of the malformations strongly suggest that genetic background or modifier genes play an important role in the phenotypic expression of HOS. Efforts to understand the intracellular pathway of TBX5 would provide a unique window onto the molecular basis of common congenital heart diseases and limb malformations.
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PMID:Current advances in Holt-Oram syndrome. 1243 37

TBX5 is a T-box transcription factor that plays a critical role in organogenesis. Seven missense mutations in TBX5 have been identified in patients with Holt-Oram syndrome characterized by congenital heart defects and upper limb abnormalities. However, the functional significance and molecular pathogenic mechanisms of these mutations are not clear. In this study we describe functional defects in DNA binding, transcriptional activity, protein-protein interaction, and cellular localization of mutant TBX5 with these missense mutations (Q49K, I54T, G80R, G169R, R237Q, R237W, and S252I). Mutations G80R, R237Q, and R237W represent a group of mutations that dramatically reduce DNA-binding activity of TBX5, leading to reduced transcription activation by TBX5 and the loss of synergy in transcriptional activation between TBX5 and NKX2.5. The second group of mutations includes Q49K, I54T, G169R, and S252I, which have no or moderate effect on DNA-binding activity and the function of transcription activation of TBX5 but cause the complete loss of synergistic transcription activity between TBX5 and NKX2.5. All seven missense mutations greatly reduced the interaction of TBX5 with NKX2.5 in vivo and in vitro. Immunofluorescent staining showed that wild type TBX5 was localized completely into the nucleus, but mutants were localized in both nucleus and cytoplasm. These results demonstrate that all seven missense mutations studied here are functional mutations with a spectrum of defects ranging from decreases in DNA-binding activity and transcriptional activation to the dramatic reduction of interaction between TBX5 and NKX2.5, and loss of synergy in transcriptional activation between these two proteins, as well as impairment in the nuclear localization of TBX5. These defects are likely central to the pathogenesis of Holt-Oram syndrome.
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PMID:Functional analysis of TBX5 missense mutations associated with Holt-Oram syndrome. 1249 78

Holt-Oram syndrome, first described in 1960, is one of many heart-hand syndromes. Upper limb involvement, predominantly radial, is universal, bilateral and asymmetrical, with variable severity. Cardiac defects occur in 95% of familial cases. Inheritance is autosomal dominant with 100% penetrance and no evidence of reduced fitness. Mutations in TBX5 have been reported in Holt-Oram syndrome. This study was conducted to establish whether a particular facial appearance is associated with Holt-Oram syndrome, one which might facilitate early diagnosis and aid differentiation from other heart-hand syndromes. Twenty-five individuals were evaluated, age 11 months to 70 years. A complete dysmorphological examination was carried out, serial photographs were reviewed, and a series of anthropometric craniofacial measurements was obtained. Subjectively, the face is square with a broad lower jaw and parietal bossing. The forehead is prominent and tall. There is narrowing at the temples. Eyes seem close-set. The nose appears relatively long, with a wide base, and short columella. With age the face becomes longer and more oval. Our anthropometric approach confirms certain clinical impressions. However, there is no objective evidence for increased face or nose height, two of the most striking features of the "gestalt." Nasal height is, in fact, reduced at all ages. There does not appear to be a syndrome-specific pattern profile to facilitate the discrimination of this condition from other heart-hand syndromes.
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PMID:Holt-Oram syndrome: is there a "face"? 1268 61

Tbx5 is a T-box transcription factor expressed exclusively in the developing forelimb but not in the developing hindlimb of vertebrates. Tbx5 is first detected in the prospective forelimb mesenchyme prior to overt limb bud outgrowth and its expression is maintained throughout later limb development stages. Direct evidence for a role of Tbx5 in forelimb development was provided by the discovery that mutations in human TBX5 cause Holt-Oram Syndrome (HOS), a dominant disorder characterised predominantly by upper(fore) limb defects and heart abnormalities. Misexpression studies in the chick have demonstrated a role for this gene in limb-type specification. Using a conditional knockout strategy in the mouse to delete Tbx5 gene function in the developing forelimb, we demonstrate that this gene is also required at early limb bud stages for forelimb bud development. In addition, by misexpressing dominant-negative and dominant-activated forms of Tbx5 in the chick wing we provide evidence that this gene is also required at later stages of limb bud development for continued limb outgrowth. Our results provide a context to understand the defects observed in HOS caused by haploinsufficiency of TBX5 in human. Moreover, our results also demonstrate that limb bud outgrowth and specification of limb identity are linked by a requirement for Tbx5.
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PMID:Tbx5 is required for forelimb bud formation and continued outgrowth. 1273 17

Mutations in TBX5, a T-box-containing transcription factor, cause cardiac and limb malformations in individuals with Holt-Oram syndrome (HOS). Mutations that result in haploinsufficiency of TBX5 are purported to cause cardiac and limb defects of similar severity, whereas missense mutations, depending on their location in the T box, are thought to cause either more severe heart or more severe limb abnormalities. These inferences are, however, based on the analysis of a relatively small number of independent cases of HOS. To better understand the relationship between mutations in TBX5 and the variable expressivity of HOS, we screened the coding and noncoding regions of TBX5 and SALL4 for mutations in 55 probands with HOS. Seventeen mutations, including six missense mutations in TBX5 and two mutations in SALL4, were found in 19 kindreds with HOS. Fewer than 50% of individuals with nonsense or frameshift mutations in TBX5 had heart and limb defects of similar severity, and only 2 of 20 individuals had heart or limb malformations of the severity predicted by the location of their mutations in the T box. These results suggest that neither the type of mutation in TBX5 nor the location of a mutation in the T box is predictive of the expressivity of malformations in individuals with HOS.
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PMID:Expressivity of Holt-Oram syndrome is not predicted by TBX5 genotype. 1278 47

Holt-Oram syndrome (HOS) is a specific developmental defect involving upper limb malformations and cardiac defects. Mutations in the TBX5 gene, located on chromosome 12q24.1, were demonstrated as the underlying molecular defect in several families with this disorder. We report on two unrelated families with HOS. Affected members of both families have the same truncation mutation in exon 5 of the TBX5 gene (Y136X). This mutation has not been reported before in HOS. The spectrum of defects is similar in both families, displaying an ASD, hypoplastic deltoid muscles and hypoplastic or absent thumbs extending to radial defects in one case. So far, only a single genotype-phenotype analysis in HOS has been done which is not sufficient to explain the high inter- and intrafamilial variability of expression. Our observation further supports that the position of the mutation in the TBX5 gene is related to the phenotype expression of HOS.
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PMID:Holt-Oram syndrome: a new mutation in the TBX5 gene in two unrelated families. 1281 25

We have recently shown that Okihiro syndrome results from mutation in the putative zinc finger transcription factor gene SALL4 on chromosome 20q13.13-13.2. There is considerable overlap of clinical features of Okihiro syndrome with other conditions, most notably Holt-Oram syndrome, a condition in part resulting from mutation of the TBX5 locus, as well as acro-renal-ocular syndrome. We analysed further families/patients with the clinical diagnosis of Holt-Oram syndrome and acro-renal-ocular syndrome for SALL4 mutations. We identified a novel SALL4 mutation in one family where the father was originally thought to have thalidomide embryopathy and had a daughter with a similar phenotype. We also found two novel mutations in two German families originally diagnosed as Holt-Oram syndrome and a further mutation in one out of two families carrying the diagnosis acro-renal-ocular syndrome. Our results show that some cases of "thalidomide embryopathy" might be the result of SALL4 mutations, resulting in an increased risk for similarly affected offspring. Furthermore we confirm the overlap of acro-renal-ocular syndrome with Okihiro syndrome at the molecular level and expand the phenotype of SALL4 mutations.
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PMID:Mutations at the SALL4 locus on chromosome 20 result in a range of clinically overlapping phenotypes, including Okihiro syndrome, Holt-Oram syndrome, acro-renal-ocular syndrome, and patients previously reported to represent thalidomide embryopathy. 1284 16


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