Thrombocytopenia absent radius syndrome with Tetralogy of Fallot: a rare association

Thrombocytopenia-Absent Radius Syndrome: Descriptions of Three New Cases and a Novel Splicing Variant in RBM8A That Expands the Spectrum of Null Alleles

Thrombocytopenia-absent radius (TAR) syndrome is a rare congenital disorder characterized by the bilateral absence of the radius and thrombocytopenia, and sometimes by other skeletal, gastrointestinal, cardiac, and renal abnormalities. The underlying genetic defect is usually the compound inheritance of a microdeletion in 1q21.1 (null allele) and a low-frequency, non-coding single nucleotide variant (SNV) in the RBM8A gene (hypomorphic allele). We report three new cases from two unrelated families. The two siblings presented the common genotype, namely the compound heterozygosity for a 1q21.1 microdeletion and the hypomorphic SNV c.-21G>A in RBM8A, whereas the third, unrelated patient presented a rare genotype comprised by two RBM8A variants: c.-21G>A (hypomorphic allele) and a novel pathogenic variant, c.343-2A>G (null allele). Of the eight documented RBM8A variants identified in TAR syndrome patients, four have hypomorphic expression and four behave as null alleles. The present report expands the RBM8A null allele spectrum and corroborates the particularities of RBM8A involvement in TAR syndrome pathogenesis.

Thrombocytopenia With Absent Radii Syndrome With an Unusual Urological Pathology: A Case Report

Thrombocytopenia with absent radii (TAR) syndrome is a rare congenital syndrome that follows an autosomal recessive pattern of inheritance. TAR syndrome is characterized by thrombocytopenia and bilateral absence (aplasia) of the radii of the forearms. This syndrome can be associated with defects within the skeletal, cardiac, renal, or gastrointestinal systems. It is important for clinicians treating patients with TAR syndrome to be aware of the myriad of complications that may arise in the other organ systems in order to promptly diagnose and treat any associated anomalies. We present a case of an African American infant diagnosed with TAR syndrome who was also found to have grade 5 vesicoureteral reflux and moderate right hydronephrosis, as well as cow's milk protein allergy.

Metacarpal Bone Plane Examination by Ultrasonography for the Diagnosis of Fetal Forearm and Hand Deformity

We explored the value of the metacarpal bone plane in screening for serious fetal forearm and hand deformities, excluding simple polydactyly and dactylion deformity, by ultrasonographic examination. Observed the second to fifth metacarpal bone plane of fetuses in 20,139 pregnant women at a gestational age of 16 to 30 weeks in The International Peace Maternity & Child Health Hospital of China Welfare Institute (IPMCH). There was a total 138 cases of fetal forearm and/or hand deformity among the 20,139 pregnant women. Of these, 134 cases were diagnosed, 4 cases were not diagnosed, and 1 case was misdiagnosed. Among the 134 diagnosed cases, there were 19 cases of hand absence, 5 cases of cleft hand, 13 cases of ectrodactyly, 26 cases of radius absence, 9 cases of forearm and hand dysplasia, 55 cases of thanatophoric dysplasia, 6 cases of wrist joint dysplasia, and 1 case of forearm amputation deformity. The deformity rate was 0.76%, the diagnostic coincidence rate was 99.97%, the sensitivity was 97.10%, the specificity was 99.99%, and the false negative rate was 2.9%. As such, careful observation of the metacarpal bone plane can be used increase the diagnosis rate of fetal forearm and hand deformity.

Thrombocytopenia-absent radius (TAR) syndrome due to compound inheritance for a 1q21.1 microdeletion and a low-frequency noncoding RBM8A SNP: a new familial case

BACKGROUND

Thrombocytopenia-absent radius syndrome (TAR; MIM 274000) is a rare autosomal recessive disorder combining specific skeletal abnormalities with a reduced platelet count. TAR syndrome has been associated with the compound inheritance of an interstitial microdeletion in 1q21.1 and a low frequency noncoding RBM8A SNP.

RESULTS

Here, we report on a patient with scapulo-humeral hypoplasia, bilateral radio-ulnar agenesis with intact thumbs, bilateral proximal positioning of the first metacarpal, bilateral fifth finger clinodactyly, bilateral radial deviation of the hands, and thrombocytopenia. Molecular studies showed compound heterozygosity for the 1q21.1 microdeletion and the RBM8A rs139428292 variant in hemizygous state, inherited from the father and the mother, respectively. A second aborted fetus presented TAR features and 1q21.1 microdeletion.

DISCUSSION

The complex inheritance pattern resulted in reduced expression of Y14, the protein encoded by RBM8A, and a component of the core exon-junction complex (EJC) in platelets. Further studies are needed to explain how Y14 insufficiency and subsequent defects of the EJC could cause the skeletal, haematological and additional features of TAR syndrome. In this study, we discuss other factors that could influence the overall phenotype of patients affected by TAR syndrome.

CONCLUSION

In this study, we discuss other factors that could influence the overall phenotype of patients affected by TAR syndrome.