Clinical and molecular characterisation of Holt-Oram syndrome focusing on cardiac manifestations

Case report: Novel TBX5-related pathogenic mechanism of Holt-Oram syndrome

Introduction: Holt-Oram syndrome (HOS) is a rare genetic disorder characterized by upper limb abnormalities, congenital heart defects, and/or conduction abnormalities. Sequence alteration of T-box transcription factor 5 (TBX5) is correlated with the incidence of HOS. Case description: We present the case of a 24-year-old female with upper limb alterations (congenital dysplasia in the wrist and elbow joints) and an anomalous left main trunk arising from the right coronary sinus. The patient inherited a base T (reference C) at rs883079 from her mother and base C (reference T) at rs10850326 from her father, both of which belong to the 3'-untranslated region (UTR) of the TBX5 gene; no alterations in TBX5 expression or single-nucleotide polymorphisms (SNPs) in other exon areas were found. We explored the effects of TBX5 on cardiomyocytes using the HL-1 cell line and TBX5-knockdown cells. Discussion: Quantitative polymerase chain reaction analysis demonstrated that TEKT2, TEKT4, and SPTB expression decreased after TBX5 knockdown, while chromatin immunoprecipitation analysis further revealed that TBX5 binds to the TEKT2, TEKT4, and SPTB promoter regions to promote gene transcription. Our findings support a novel TBX5-related pathogenic mechanism in HOS.

Functional analysis of two novel TBX5 variants present in individuals with Holt-Oram syndrome with different clinical manifestations

Holt-Oram syndrome (HOS) is a rare disorder characterized by cardiac and upper-limb defects. Pathogenic variants in TBX5-a gene encoding a transcription factor important for heart and skeletal development-are the only known cause of HOS. Here, we present the identification and functional analysis of two novel TBX5 pathogenic variants found in two individuals with HOS presenting distinct phenotypes. The individual with the c.905delA variant has a severe cardiac phenotype but mild skeletal defects, unlike the individual with the c.246_249delGATG variant who has no cardiac problems but severe upper limbs malformations, including phocomelia. Both frameshift variants, c.246_249delGATG and c.905delA, generate mRNAs harbouring premature stop codons which, if not degraded by nonsense mediated decay, will lead to the production of shorter TBX5 proteins, p.Gln302Argfs*92 and p.Met83Phefs*6, respectively. Immunocytochemistry results suggest that both mutated proteins are produced and furthermore, like the wild-type protein, p.Gln302Argfs*92 mutant appears to be mainly localized in the nucleus, in contrast with p.Met83Phefs*6 mutant that displays a higher level of cytoplasmic localization. In addition, luciferase activity analysis revealed that none of the TBX5 mutants are capable of transactivating the NPPA promoter. In conclusion, our results provide evidence that both pathogenic variants cause a severe TBX5 loss-of-function, dramatically reducing its biological activity. The absence of cardiac problems in the individual with the p.Met83Phefs*6 variant supports the existence of other mechanisms/genes underlying the pathogenesis of HOS and/or the existence of an age-related delay in the development of a more serious cardiac phenotype. Further studies are required to understand the differential effects observed in the phenotypes of both individuals.

Familial dilated cardiomyopathy associated with pathogenic TBX5 variants: Expanding the cardiac phenotype associated with Holt-Oram syndrome

Holt-Oram syndrome (HOS) is a rare, autosomal dominant disorder caused by heterozygous pathogenic variants in cardiac T-box transcription factor, TBX5. Classically, it is associated with upper limb malformations and variable cardiac abnormalities. Limb manifestations are considered to be invariably present, ranging in severity from limitation in movement, to triphalangeal thumbs, absent thumbs, shortened forearms, or phocomelia. Cardiac involvement is characterized by congenital heart defects, most commonly septal structural malformations, and conduction system disease. Recently, novel TBX5 variants have also been reported in association with dilated cardiomyopathy (DCM). In this context, we report eight individuals from four unrelated families, in whom pathogenic variants in TBX5 segregated with an atypical HOS phenotype. Affected individuals exhibit relatively mild skeletal features of HOS, with a predominant cardiac phenotype, which includes several individuals affected by non-ischaemic DCM. To our knowledge, these represent the first reported cases of DCM in families with skeletal features of HOS, some of whom also harbored variants previously linked to a classical HOS phenotype (p. Arg279* and p.Arg237Gln). This finding supports diverse roles of TBX5 in cardiovascular development and function, and confirms the importance of long-term cardiac surveillance for individuals affected by HOS. Furthermore, these families highlight the wide phenotypic variability of HOS, which may include comparatively mild upper limb findings in respect to cardiac manifestations.

Asymptomatic phaeochromocytoma in a patient with Holt-Oram syndrome: a case report

Background

Holt-Oram syndrome (HOS) is a rare congenital disease that affects the heart and upper limbs. Phaeochromocytoma, a catecholamine-secreting tumour, is a rare neuroendocrine disorder. We present an interesting case presentation of these two rare disorders in a patient who was asymptomatic for phaeochromocytoma.

Case summary

A 28-year-old woman who was diagnosed at birth with HOS, presented to the hospital with heart failure. She has a past medical history of corrected cyanotic congenital heart disease. She presented with dyspnoea but she did not have headaches, tremors, or diaphoresis. Cardiac magnetic resonance scan was done to investigate the cause of her heart failure and revealed right ventricular systolic dysfunction and a suspicious adrenal lesion. Magnetic resonance imaging adrenal confirmed the presence of the adrenal lesion and concerns were raised for a possible phaeochromocytoma. Biochemical tests showed raised plasma free metanephrine levels. Gallium-68 DOTA positron emission tomography scan showed intense right adrenal gland uptake in keeping with diagnosis of phaeochromocytoma.

Discussion

Phaeochromocytoma appears to be more prevalent in patients who are in a chronic hypoxic state. This hypoxic state has been postulated to cause the proliferation of adrenal tissue and therefore the formation of phaeochromocytomas. The hypoxia-inducing factor, which is increased in patients with phaeochromocytoma, has been identified as one of the key factors driving this process as it modulates genes that regulate angiogenesis and proliferation. Congenital heart defects seen in HOS can progress to cyanotic heart disease if left uncorrected and may have been the driver for the development of phaeochromocytoma in our patient.

Clinical and epidemiological features of Heart-Hand Syndrome: a hospital-based study in China

Heart–hand syndrome (HHS) is a clinically and genetically heterogeneous disorder characterized by the co-occurrence of a congenital cardiac disease and an upper limb malformation. This study revealed the clinical and epidemiological features of HHS in China. The study was based on patients with congenital upper limb malformation treated in Beijing Ji Shui Tan hospital from October 1^st, 2013 to October 1^st, 2016. We reviewed the patients’ medical records and identified patients with abnormal ultrasonic cardiogram and/or electrocardiogram (ECG). A total of 1462 patients (910 male and 552 female) were identified to be treated for congenital upper limb malformation. Among them, 172 (11.8%) had abnormal ultrasonic cardiogram and/or ECG. Abnormal heart structure were discovered in 121 patients and 51 patients had abnormal ECG. The most common type of abnormal heart structure was tricuspid regurgitation (53/121, 43.8%), while the most common abnormal ECG was wave patterns (22/51, 43.1%). This hospital-based study suggests that the rate of congenital heart disease is high in patients treated for congenital upper extremity malformation in China. Surgeons and anesthetists should be aware of the comorbidity and preoperational examination of congenital heart diseases is highly needed to avoid complications during operation.

NUP155 insufficiency recalibrates a pluripotent transcriptome with network remodeling of a cardiogenic signaling module

BACKGROUND

Atrial fibrillation is a cardiac disease driven by numerous idiopathic etiologies. NUP155 is a nuclear pore complex protein that has been identified as a clinical driver of atrial fibrillation, yet the precise mechanism is unknown. The present study employs a systems biology algorithm to identify effects of NUP155 disruption on cardiogenicity in a model of stem cell-derived differentiation.

METHODS

Embryonic stem (ES) cell lines (n = 5) with truncated NUP155 were cultured in parallel with wild type (WT) ES cells (n = 5), and then harvested for RNAseq. Samples were run on an Illumina HiSeq 2000. Reads were analyzed using Strand NGS, Cytoscape, DAVID and Ingenuity Pathways Analysis to deconvolute the NUP155-disrupted transcriptome. Network topological analysis identified key features that controlled framework architecture and functional enrichment.

RESULTS

In NUP155 truncated ES cells, significant expression changes were detected in 326 genes compared to WT. These genes segregated into clusters that enriched for specific gene ontologies. Deconvolution of the collective framework into discrete sub-networks identified a module with the highest score that enriched for Cardiovascular System Development, and revealed NTRK1/TRKA and SRSF2/SC35 as critical hubs within this cardiogenic module.

CONCLUSIONS

The strategy of pluripotent transcriptome deconvolution used in the current study identified a novel association of NUP155 with potential drivers of arrhythmogenic AF. Here, NUP155 regulates cardioplasticity of a sub-network embedded within a larger framework of genome integrity, and exemplifies how transcriptome cardiogenicity in an embryonic stem cell genome is recalibrated by nucleoporin dysfunction.

Genetic Analyses Identified a SALL4 Gene Mutation Associated with Holt-Oram Syndrome

Holt-Oram syndrome (HOS) is an autosomal dominant disorder, which is characterized by deformities of upper limbs and congenital heart defects. Alterations of TBX5 gene have been identified to be the leading cause of HOS, while some cases could not be explained by TBX5 mutations. In our study, we preliminarily diagnosed a newborn baby, who had Tetralogy of Fallot, thumb agenesis, facial dysplasia, and right ear canal malformation, as HOS. Chromosome microarray analyses showed no pathological deletions or replications of chromosome segments; whole exome sequencing screened out six candidate genes that were involved in cardiac diseases or syndromes among which SALL4 has been reported as HOS related gene. We evaluated the pathogenicity of SALL4 mutant sites by series of software. The results indicated that SALL4-M143V may be a polymorphism site, and SALL4-R418C could cause disease. HOPE and SWISS PDB viewer showed that SALL4-R418C leads to changes in amino acid properties, loss of protein hydrogen bond, and functional impact of SALL4 zinc finger domain. These results further confirmed the pathogenic significance of SALL4-R418C mutant. When genetic analyses coupled with bioinformatic analyses, we identified a SALL4 gene rare mutation which might contribute to a newborn with HOS. Although some doubts need to be further discussed and explored, our study deepened the understanding of phenotype difference among syndromes and role of SALL4 mutations in disease occurrence.