Whole exome sequencing identifies genetic variants in inherited thrombocytopenia with secondary qualitative function defects.

Inherited thrombocytopenias are a heterogeneous group of disorders characterized by abnormally low platelet counts which can be associated with abnormal bleeding. Next-generation sequencing has previously been employed in these disorders for the confirmation of suspected genetic abnormalities, and more recently in the discovery of novel disease-causing genes. However its full potential has not yet been exploited. Over the past 6 years we have sequenced the exomes from 55 patients, including 37 index cases and 18 additional family members, all of whom were recruited to the UK Genotyping and Phenotyping of Platelets study. All patients had inherited or sustained thrombocytopenia of unknown etiology with platelet counts varying from 11×109/L to 186×109/L. Of the 51 patients phenotypically tested, 37 (73%), had an additional secondary qualitative platelet defect. Using whole exome sequencing analysis we have identified "pathogenic" or "likely pathogenic" variants in 46% (17/37) of our index patients with thrombocytopenia. In addition, we report variants of uncertain significance in 12 index cases, including novel candidate genetic variants in previously unreported genes in four index cases. These results demonstrate that whole exome sequencing is an efficient method for elucidating potential pathogenic genetic variants in inherited thrombocytopenia. Whole exome sequencing also has the added benefit of discovering potentially pathogenic genetic variants for further study in novel genes not previously implicated in inherited thrombocytopenia.

Chediak-Higashi syndrome: description of two novel homozygous missense mutations causing divergent clinical phenotype.

Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disease resulting from mutations in the LYST/CHS1 gene, which encodes for a 429 kDa protein, CHS1/LYST, that regulates vesicle trafficking and determines the size of lysosomes and other organelles. To date, 60 different mutations have been characterized, and a reasonably straightforward phenotype-genotype correlation has been suggested. We describe two patients on opposite ends of the CHS clinical spectrum with novel missense mutations. We characterized these patients in terms of their mutations, protein localization and expression, mRNA stability, and electrostatic potential. Patient 1 is the first report of a severe early-onset CHS with a homozygous missense mutation (c.11362 G>A, p.G3725R) in the LYST/CHS1 gene. This molecular change results in a reduction at the CHS1 protein level, not due to an mRNA effect, but maybe a consequence of both, a change in the structure of the protein and most likely attributable to the remarkable serious perturbation in the electrostatic potential. Patient 2, who exhibited the adolescence form of the disease, was found to be homozygous for a novel missense mutation c.961 T>C, p.C258R, which seemed to have minor effect on the structure of the CHS1/LYST protein. Reexamining accepted premises of missense mutant alleles being reported among patients with clinically mild forms of the disorder should be carried out, and attempts to link genotype and clinical phenotype require identifying the actual molecular effect of the mutation. Early and accurate diagnosis of the severity of the disease is extremely important to early differentiate patients who would benefit from premature enrollment into a transplantation protocol.

Allogeneic hematopoietic cell transplantation in an adult patient with Glanzmann thrombasthenia.

Glanzmann thrombasthenia is a rare bleeding disorder that can present life-threatening bleeding. Our patients develop antiplatelet antibodies that become refractory to any pharmacological treatment. Allogeneic hematopoietic stem-cell transplantation is the only currently curative procedure, but has major risks mainly in adult; indeed, our patient died.

Towards the targeted management of Chediak-Higashi syndrome.

Chediak-Higashi syndrome (CHS) is a rare, autosomal recessive congenital immunodeficiency caused by mutations in CHS1, a gene encoding a putative lysosomal trafficking protein. In the majority of patients, this disorder is typically characterized by infantile-onset hemophagocytic lymphohistiocytosis (HLH), which is lethal unless allogeneic transplantation is performed. A small number of individuals have the attenuated form of the disease and do not benefit from transplant. Improved outcomes of transplantation have been reported when performed before the development of HLH, thus it is important to quickly differentiate patients that present with the childhood form of disease and to prematurely enroll them into a transplantation protocol. In addition, this would also preclude those that exhibit clinical phenotypes of adolescent and adult CHS from this treatment. Patients with an absence of cytotoxic T lymphocyte (CTL) function have a high risk for developing HLH, and could therefore benefit the most from early hematopoietic stem cell transplantation (HSCT). However, although normal CTL cytotoxicity or bi-allelic missense mutations do not exclude the occurrence of HLH in childhood, a more conservative approach is justified. This article summarizes recent advances in the clinical characterization of CHS patients, provides updates on promising new testing methods, and focuses on specific therapeutic approaches.

Functional and molecular characterization of inherited platelet disorders in the Iberian Peninsula: results from a collaborative study.

BACKGROUND: The diagnostic evaluation of inherited platelet disorders (IPDs) is complicated and time-consuming, resulting in a relevant number of undiagnosed and incorrectly classified patients. In order to evaluate the spectrum of IPDs in individuals with clinical suspicion of these disorders, and to provide a diagnostic tool to centers not having access to specific platelets studies, we established the project "Functional and Molecular Characterization of Patients with Inherited Platelet Disorders" under the scientific sponsorship of the Spanish Society of Thrombosis and Haemostasis. PATIENTS/METHODS: Subjects were patients from a prospective cohort of individuals referred for clinical suspicion of IPDs as well as healthy controls. Functional studies included light transmission aggregation, flow cytometry, and when indicated, Western-blot analysis of platelet glycoproteins, and clot retraction analysis. Genetic analysis was mainly performed by sequencing of coding regions and proximal regulatory regions of the genes of interest. RESULTS: Of the 70 cases referred for study, we functionally and molecularly characterized 12 patients with Glanzmann Thrombasthenia, 8 patients with Bernard Soulier syndrome, and 8 with other forms of IPDs. Twelve novel mutations were identified among these patients. The systematic study of patients revealed that almost one-third of patients had been previously misdiagnosed. CONCLUSIONS: Our study provides a global picture of the current limitations and access to the diagnosis of IPDs, identifies and confirms new genetic variants that cause these disorders, and emphasizes the need of creating reference centers that can help health care providers in the recognition of these defects.