First reported adult patient with TARP syndrome: A case report

Nuclear speckleopathies: developmental disorders caused by variants in genes encoding nuclear speckle proteins

Nuclear speckles are small, membrane-less organelles that reside within the nucleus. Nuclear speckles serve as a regulatory hub coordinating complex RNA metabolism steps including gene transcription, pre-mRNA splicing, RNA modifications, and mRNA nuclear export. Reflecting the importance of proper nuclear speckle function in regulating normal human development, an increasing number of genetic disorders have been found to result from mutations in the genes encoding nuclear speckle proteins. To denote this growing class of genetic disorders, we propose "nuclear speckleopathies". Notably, developmental disabilities are commonly seen in individuals with nuclear speckleopathies, suggesting the particular importance of nuclear speckles in ensuring normal neurocognitive development. In this review article, a general overview of nuclear speckle function, and the current knowledge of the mechanisms underlying some nuclear speckleopathies, such as ZTTK syndrome, NKAP-related syndrome, TARP syndrome, and TAR syndrome, are discussed. These nuclear speckleopathies represent valuable models to understand the basic function of nuclear speckles and how its functional defects result in human developmental disorders.

RNA binding proteins in cardiovascular development and disease

Congenital heart disease (CHD) is the most common birth defect affecting>1.35 million newborn babies worldwide. CHD can lead to prenatal, neonatal, postnatal lethality or life-long cardiac complications. RNA binding protein (RBP) mutations or variants are emerging as contributors to CHDs. RBPs are wizards of gene regulation and are major contributors to mRNA and protein landscape. However, not much is known about RBPs in the developing heart and their contributions to CHD. In this chapter, we will discuss our current knowledge about specific RBPs implicated in CHDs. We are in an exciting era to study RBPs using the currently available and highly successful RNA-based therapies and methodologies. Understanding how RBPs shape the developing heart will unveil their contributions to CHD. Identifying their target RNAs in the embryonic heart will ultimately lead to RNA-based treatments for congenital heart disease.

Functional insight into a neurodevelopmental disorder caused by missense variants in an RNA-binding protein, RBM10

The RNA-binding motif protein 10, RBM10, is an RNA splicing regulator essential for development. Loss-of-function RBM10 variants are associated with TARP syndrome, a severe X-linked recessive condition in males. We report a 3-year-old male with a mild phenotype, consisting of cleft palate, hypotonia, developmental delay, and minor dysmorphisms, associated with a missense RBM10 variant, c.943T>C, p.Ser315Pro, affecting the RRM2 RNA-binding domain. His clinical features were similar to a previously reported case associated with a missense variant. The p.Ser315Pro mutant protein was expressed normally in the nucleus, but its expression level and protein stability were slightly reduced. Nuclear magnetic resonance spectroscopy showed that the structure and the RNA-binding ability of the RRM2 domain with the p.Ser315Pro were unaffected. However, it affects the alternative splicing regulations of downstream genes, NUMB and TNRC6A, and its splicing alteration patterns were variable depending on target transcripts. In summary, a novel germline missense RBM10 p.Ser315Pro variant that causes functional changes in the expression of its downstream genes results in a non-lethal phenotype associated with developmental delays. The functional alteration effects depend on the residues affected by missense variants. Our findings are expected to bring broader insights into the RBM10-associated genotype-phenotype relationships by delineating the molecular mechanism of RBM10 functions.

Vitelline vascular remnant causing intestinal obstruction in a patient with TARP syndrome

BACKGROUND

TARP syndrome, characterized by talipes equinovarus, atrial septal defect, Robin sequence, and persistent left superior vena cava, is an X-linked recessive condition caused by deleterious variants in RBM10. Vitelline vascular remnants (VVR) are a rare vitelline duct anomaly with approximately 26 cases previously reported. There are no previously reported cases of VVRs in patients with TARP syndrome.

CASE

We present a male neonate diagnosed with TARP syndrome via trio whole exome sequencing who had classic features of this syndrome, although his course was additionally complicated by feeding intolerance with multiple episodes of abdominal distension. Serial imaging and contrast studies of the upper GI tract and small bowel demonstrated small bowel obstruction of unclear etiology. Given the poor prognosis associated with this condition, life-sustaining measures were withdrawn, and he passed away at 38 days of age. On autopsy, a VVR was unexpectedly identified with proximal bowel dilation, explaining his feeding intolerance.

CONCLUSIONS

We highlight the importance of full post-mortem examination in understanding the complete spectrum of manifestations of genetic syndromes and provide a review of the literature.

Abnormal liver function tests and improved survival in a child with splice mutation TARP syndrome

TARP (talipes equinovarus, atrial septal defect (ASD), Robin sequence, persistent left superior vena cava) syndrome is a rare X-linked disorder affecting the RBM10 gene. It was previously viewed as universally fatal in the early neonatal period, however, recent cases have shown patients surviving beyond this stage. We present a male toddler diagnosed with TARP syndrome due to a a previously unreported splicing mutation c.2295+1G>A in the RBM10 gene. At birth, he had an ASD and Robin sequence, two of the eponymous features, as well as other associated phenotypic features. During infancy, he had an extremely high alpha-fetoprotein, conjugated hyperbilirubinaemia and thrombocytopaenia, features not previously described in TARP syndrome. We discuss these findings as well as our patient's survival past the neonatal period with special consideration to recent genotype-phenotypes correlations.

A Frameshift RBM10 Variant Associated With TARP Syndrome

TARP syndrome is a rare X-linked genetic condition caused by mutations in the RBM10 gene. Primary clinical characteristics of TARP syndrome include Talipes equinovarus, Atrial septal defect, Robin sequence and Persistent left superior vena cava. Newly reported cases identified a few novel RBM10 variants and atypical manifestations associated with TARP syndrome, thus expanding the genetic and clinical spectrum of TARP syndrome. Here we report a molecularly confirmed TARP syndrome with distinctive clinical features including pulmonary arteriovenous malformation, single umbilical artery, and coagulopathy. We identified a frameshift RBM10 variant that might be associated with his distinctive clinical features.

RBM10: Structure, functions, and associated diseases

RBM10 is a nuclear RNA-binding protein (RBP) that regulates the alternative splicing of primary transcripts. Recently, research on RBM10 has become increasingly active owing to its clinical importance, as indicated by studies on RBM0 mutations that cause TARP syndrome, an X-linked congenital pleiotropic developmental anomaly, and various cancers such as lung adenocarcinoma in adults. Herein, the molecular biology of RBM10 and its significance in medicine are reviewed, focusing on the gene and protein structures of RBM10, its cell biology, molecular functions and regulation, relationship with the paralogous protein RBM5, and the mutations of RBM10 and their associated diseases. Finally, the challenges in future studies of RBM10 are discussed in the concluding remarks.

TARP syndrome associated with renal malformation and optic nerve atrophy

Talipes equinovarus, atrial septal defect, Robin sequence and persistent left superior vena cava (TARP) syndrome is a congenital disease caused by mutations in the RBBM10 gene. It has a low prevalence and a high rate of mortality in the neonatal stage. In this case report, we present a case of a 32-week gestational age preterm newborn with a prenatal diagnosis of intrauterine growth restriction, with a persistent left superior vena cava, interatrial communication and a horseshoe kidney. Additionally, postnatal optic nerve atrophy was diagnosed. By using exome sequencing, the pathogenic variant c.1877del; p.his626Lefus*78 was identified in the RMB10 gene. Due to a lack of reports in the medical literature, the phenotype has not fully been described. Here, we report on a patient with TARP syndrome and a previously unreported mutation, c.1877del; p.his627Leufs*78, which is predicted to generate a truncated and/or protein decay of the RBM10 transcript.

Genetic Mutations Associated with Pierre Robin Syndrome/Sequence: A Systematic Review

Pierre Robin syndrome/sequence (PRS) is associated with a triad of symptoms that includes micrognathia, cleft palate, and glossoptosis that may lead to respiratory obstruction. The syndrome occurs in 2 forms: nonsyndromic PRS (nsPRS), and PRS associated with other syndromes (sPRS). Studies have shown varying genetic mutations associated with both nsPRS and sPRS. The present systematic review aims to provide a comprehensive collection of published literature reporting genetic mutations in PRS. Web of Science, PubMed, and Scopus were searched using the keywords: "Pierre Robin syndrome/sequence AND gene mutation." The search resulted in 208 articles, of which 93 were excluded as they were duplicates/irrelevant. The full-text assessment led to the further exclusion of 76 articles. From the remaining 39 articles included in the review, details of 324 cases were extracted. 56% of the cases were sPRS, and 22% of the cases were associated with other malformations and the remaining were nsPRS. Genetic mutations were noted in 30.9% of the 300 cases. Based on the review, SOX9 was found to be the most common gene associated with both nsPRS and sPRS. The gene mutation in sPRS was specific to the associated syndrome. Due to the lack of original studies, a quantitative analysis was not possible. Thus, future studies must focus on conducting large-scale cohort studies. Along with generating data on genetic mutation, future studies must also conduct pedigree analysis to assess potential familial inheritance, which in turn could provide valuable insights into the etiopathogenesis of PRS.

Phenotypic spectrum of the RBM10-mediated intellectual disability and congenital malformation syndrome beyond classic TARP syndrome features

Pathogenic variants in the RBM10 gene cause a rare X-linked disorder described as TARP (Talipes equinovarus, Atrial septal defect, Robin sequence, and Persistent left vena cava superior) syndrome. We report two novel patients with truncating RBM10 variants in view of the literature, presenting a total of 26 patients from 15 unrelated families. Our results illustrate the highly pleiotropic nature of RBM10 pathogenic variants, beyond the classic TARP syndrome features. Major clinical characteristics include severe developmental delay, failure to thrive, brain malformations, neurological symptoms, respiratory issues, and facial dysmorphism. Minor features are growth retardation, cardiac, gastrointestinal, limb, and skeletal abnormalities. Additional recurrent features include genital and renal abnormalities as well as hearing and visual impairment. Thus, RBM10 loss of function variants typically cause an intellectual disability and congenital malformation syndrome that requires assessment of multiple organ systems at diagnosis and for which provided clinical features might simplify diagnostic assessment. Furthermore, evidence for an RBM10-related genotype-phenotype correlation is emerging, which can be important for prognosis.

Updates on congenital lacrimal drainage anomalies and their association with syndromes and systemic disorders: A major review

BACKGROUND

To review and update the syndromic and non-syndromic systemic associations of congenital lacrimal drainage anomalies.

METHODS

The authors performed a PubMed search of all articles published in English on congenital lacrimal drainage anomalies (CLDA). The current review provides an update from January 2017 to August 2020 on all CLDA associated with clinical syndromes or non-syndromic systemic disorders. The update intends to appraise the readers on all papers that were published in the interim 3-year period since the publication of the previous major review by authors (1933-2016). Patients with specific syndromes or systemic disorders were then reviewed. Pertinent cross-references from each of the short-listed articles were also included. Data reviewed include syndromic descriptions, systemic details, demographics, lacrimal presentations, management, and outcomes.

RESULTS

There have been significant new updates. Eleven new syndromes have been added to the list of syndromic associations, of which three were suspects. Among the new syndromic associations, three (PHACE, Williams-Beuren, and Peter's plus syndromes) described CLDA details in depth. Several new non-syndromic systemic conditions with associated CLDA also came to light, the foremost amongst them being proboscis lateralis, diprosopus dirrhinus, cerebral palsy, and NGLY-1 related disorders. Although familial presentations have been reported, the inheritance patterns are unclear for most anomalies. Surgical challenges in these patients are distinct, and a thorough pre-operative assessment, including detailed imaging when indicated, may facilitate good outcomes. Two updated tables reflecting the summary of syndromic and non-syndromic systemic associations are provided to capture the details at a glance.

CONCLUSION

It is not very uncommon to find CLDA in syndromic or non-syndromic systemic disorders. Diagnosis of a craniofacial syndrome should prompt the physician to look out for CLDA. Similarly, a diagnosis of multiple CLDA should alert the examiner for the possible presence of associated systemic anomalies.

A novel missense variant in RBM10 can cause a mild form of TARP syndrome with developmental delay and dysmorphic features

RBM10, is an RNA binding protein that is important for development by regulating the expression of multiple genes. RBM10 is on the X chromosome, and nonsense and frameshift RBM10 variants cause TARP syndrome in males. In a 4-year-old male, we identified a novel maternally inherited missense RBM10 variant in the RRM2 RNA binding domain, c.965C>T, p.Pro322Leu. His clinical features included intellectual disability, developmental delay, growth restriction, hypotonia, and craniofacial malformations. These features were much milder than those described in previously reported cases of TARP syndrome. By in vitro assays, we found that the mutant p.Pro322Leu RBM10 protein retained its specific RNA binding capacity, while gaining a low-affinity nonspecific RNA binding. It was normally localized to the nucleus, but its expression level was significantly reduced with a significantly short half-life. These results indicated that the p.Pro322Leu missense variant causes a developmental disorder in humans through a unique loss-of-function mechanism.

First reported adult patient with TARP syndrome: A case report

TARP syndrome (talipes equinovarus, atrial septal defect, Robin sequence, and persistence of the left superior vena cava) is a rare X‐linked syndrome often resulting in pre‐ or post‐natal lethality in affected males. In 2010, RBM10 was identified as the disease‐causing gene, and we describe the first adult patient with TARP syndrome at age 28 years, hereby expanding the phenotypic spectrum. Our patient had Robin sequence, atrial septal defect, intellectual disability, scoliosis, and other findings previously associated with TARP syndrome. In addition, he had a prominent nose and nasal bridge, esotropia, displacement of lacrimal points in the cranial direction, small teeth, and chin dimple, which are the findings that have not previously been associated with TARP syndrome. Our patient was found to carry a hemizygous c.273_283delinsA RBM10 mutation in exon 4, an exon skipped in three of five protein‐coding transcripts, suggesting a possible explanation for our patient surviving to adulthood. Direct sequencing of maternal DNA indicated possible mosaicism, which was confirmed by massive parallel sequencing. One of two sisters were heterozygous for the mutation. Therefore, we recommend sisters of patients with TARP syndrome be carrier tested before family planning regardless of carrier testing results of the mother. Based on our patient and previously reported patients, we suggest TARP syndrome be considered as a possible diagnosis in males with severe or profound intellectual disability combined with septal heart defect, and Robin sequence, micrognathia, or cleft palate.