No genetic abnormalities identified in α2IIb and β3: phenotype overcomes genotype in Glanzmann thrombasthenia

Classic Light Transmission Platelet Aggregometry: Do We Still Need it?

For more than 50 years, light transmission aggregometry has been accepted as the gold standard test for diagnosing inherited platelet disorders in platelet-rich plasma, although there are other functional approaches performed in whole blood. In this article, several advantages and disadvantages of this technique over other laboratory approaches are discussed in the view of recent guidelines, and the necessity of functional assays, such as light transmission aggregometry in the era of molecular genetic testing, is highlighted.

A novel heterozygous mutation flanking the fourth calcium-binding domain of the ITGA2B gene induces severe bleeding complications: a case report and literature review

Glanzmann thrombasthenia is a rare autosomal recessive genetic disease characterized by platelet aggregation dysfunction caused by a congenital defect of platelet membrane glycoprotein IIb/IIIa (integrin αIIbβ3). Integrin αIIbβ3, a calcium-dependent heterodimer, plays a critical role in platelet aggregation. We described a boy who was hospitalized with serious epistaxis at 10 months of age who had a history of repeated petechiae and spontaneous epistaxis since birth. Flow cytometry showed normal surface expression of platelet antigens. Genetic analysis and sequencing revealed the novel missense mutation c.G1252>T (p.Gly418Cys) in ITGA2B. This heterozygous amino acid mutation flanked the fourth calcium-binding domain and may interfere with integrin biogenesis via mechanisms other than merely altering cell surface expression. We discuss the heterogeneity of the genotype and phenotype with this atypical case and review the relevant literature on mutations adjacent to or within the calcium-binding domains in Glanzmann thrombasthenia.

Retinal hemorrhage and bleeding disorders in children: A review

BACKGROUND

Retinal hemorrhages (RH) are a common manifestation of abusive head trauma (AHT) resulting from acceleration-deceleration injury with or without blunt impact. Evaluation of a child with RH requires careful consideration of these differential diagnoses. The extent to which coagulopathy alone can cause RH would be useful to understand as coagulopathy may accompany AHT.

OBJECTIVE

In this systematic review, we sought to identify whether coagulopathies have been reported with RH similar to those of AHT.

METHODS

We performed a literature search for ocular manifestations of bleeding disorders in children less than 18 years old. We included clotting factor deficiencies, vitamin K deficiency, platelet function abnormalities, thrombocytopenia, disseminated intravascular coagulation (DIC), and trauma induced coagulopathy (TIC). We included only pediatric reports of intraocular bleeding or documented eye examinations that indicated no hemorrhages. We then re-examined cases for ocular and systemic findings that could potentially mimic abuse.

RESULTS

Our initial search yielded 816 results. Sixty-one articles met our inclusion criteria. Of these, there were 32 children within the AHT age range (less than 5 years old) who had RH and concomitant coagulopathy. Only 5 cases might potentially be confused for abuse. Of these, no classic characteristics of RH from abuse such as retinoschisis or retinal folds were found. Systemic features were inconsistent with AHT.

CONCLUSIONS

The presence of coagulopathy alone does not rule out the possibility that the child has been abused. Coagulopathy alone has not been reported as an etiology of RH that are consistent with AHT, especially when other findings are present.

Introducing high-throughput sequencing into mainstream genetic diagnosis practice in inherited platelet disorders

Inherited platelet disorders are a heterogeneous group of rare diseases, caused by inherited defects in platelet production and/or function. Their genetic diagnosis would benefit clinical care, prognosis and preventative treatments. Until recently, this diagnosis has usually been performed via Sanger sequencing of a limited number of candidate genes. High-throughput sequencing is revolutionizing the genetic diagnosis of diseases, including bleeding disorders. We have designed a novel high-throughput sequencing platform to investigate the unknown molecular pathology in a cohort of 82 patients with inherited platelet disorders. Thirty-four (41.5%) patients presented with a phenotype strongly indicative of a particular type of platelet disorder. The other patients had clinical bleeding indicative of platelet dysfunction, but with no identifiable features. The high-throughput sequencing test enabled a molecular diagnosis in 70% of these patients. This sensitivity increased to 90% among patients suspected of having a defined platelet disorder. We found 57 different candidate variants in 28 genes, of which 70% had not previously been described. Following consensus guidelines, we qualified 68.4% and 26.3% of the candidate variants as being pathogenic and likely pathogenic, respectively. In addition to establishing definitive diagnoses of well-known inherited platelet disorders, high-throughput sequencing also identified rarer disorders such as sitosterolemia, filamin and actinin deficiencies, and G protein-coupled receptor defects. This included disease-causing variants in DIAPH1 (n=2) and RASGRP2 (n=3). Our study reinforces the feasibility of introducing high-throughput sequencing technology into the mainstream laboratory for the genetic diagnostic practice in inherited platelet disorders.