Hereditary Thrombotic Thrombocytopenic Purpura in a 9-Month-old: Diagnosing and Managing an Ultra-rare Disorder.

Hereditary thrombotic thrombocytopenic purpura is an ultra-rare disorder caused by biallelic mutations in the ADAMTS13 gene. Because it can be difficult to diagnose, plasma ADAMTS13 activity assessment should be considered in patients with thrombocytopenia, anemia, and schistocytes on peripheral blood smear. We present the diagnostic evaluation of a patient with hereditary thrombotic thrombocytopenic purpura. Genetic testing revealed one known pathogenic mutation and one novel mutation of ADAMTS13 classified as likely pathogenic on the basis of parental genetic testing and in silico analyses. We further discuss off-label use of prophylactic plasma-derived Factor VIII (Koate-DVI) and the benefit of rare disease registries.

An Erythrocytosis-Associated Mutation in the Zinc Finger of PHD2 Provides Insights into Its Binding of p23.

BACKGROUND: Loss of function mutations in the EGLN1 gene are a cause of erythrocytosis. EGLN1 encodes for prolyl hydroxylase domain protein 2 (PHD2). PHD2 hydroxylates and downregulates hypoxia-inducible factor-2α (HIF-2α), a transcription factor that regulates erythropoiesis. While the large majority of erythrocytosis-associated EGLN1 mutations occur within its catalytic domain, rare mutations reside in its zinc finger. This zinc finger binds a Pro-Xaa-Leu-Glu motif in p23, an HSP90 cochaperone that facilitates hydroxylation of HIF-α, an HSP90 client. Essentially nothing is known about the specific interactions between the PHD2 zinc finger and p23. RESULTS: Here, we characterize an erythrocytosis-associated mutation in the zinc finger, K55N, that abolishes interaction with p23. We provide evidence that the affected residue, Lys-55, interacts with Asp-152 of p23. We also present results that indicate that PHD2 Arg-32 interacts with p23 Glu-160. CONCLUSION: These studies not only reinforce the importance of the PHD2 zinc finger in the control of erythropoiesis, but also lead to a model in which a peptide motif in p23 binds in a specific orientation to a predicted groove in the zinc finger of PHD2.

Case Report: Development of Factor VIII Inhibitor in a Patient with an Uncommon de novo Mutation in the Factor VIII Gene.

The development of factor VIII inhibitors remains a significant clinical challenge in the management of hemophilia A. We present a patient of mixed ethnicity with severe hemophilia A who was found to have a F8 gene hemizygous c.5815G>T mutation resulting in an Ala1939Ser substitution (Ala1920Ser in legacy nomenclature) and possible splice site change that has been reported in only 1 patient previously. He developed an inhibitor shortly after starting replacement recombinant factor VIII (Advate®; Baxalta, Bannockburn, IL, USA) and was successfully treated with immune tolerance therapy. Our report describes the second patient reported to have severe hemophilia due to this mutation and the only case of a factor VIII inhibitor associated with this mutation.

Severe bleeding with subclinical oculocutaneous albinism in a patient with a novel HPS6 missense variant.

Hermanský-Pudlák syndrome (HPS), a rare autosomal recessive disorder, manifests with oculocutaneous albinism and a bleeding diathesis. However, severity of disease can be variable and is typically related to the genetic subtype of HPS; HPS type 6 (HPS-6) is an uncommon subtype generally associated with mild disease. A Caucasian adult female presented with a history of severe bleeding; ophthalmologic examination indicated occult oculocutaneous albinism. The patient was diagnosed with a platelet storage pool disorder, and platelet whole mount electron microscopy demonstrated absent delta granules. Genome-wide SNP analysis showed regions of homozygosity that included the HPS1 and HPS6 genes. Full length HPS1 transcript was amplified by PCR of genomic DNA. Targeted next-generation sequencing identified a novel homozygous missense variant in HPS6 (c.383 T > C; p.V128A); this was associated with significantly reduced HPS6 mRNA and protein expression in the patient's fibroblasts compared to control cells. These findings highlight the variable severity of disease manifestations in patients with HPS, and illustrate that HPS can be diagnosed in patients with excessive bleeding and occult oculocutaneous albinism. Genetic analysis and platelet electron microscopy are useful diagnostic tests in evaluating patients with suspected HPS. Clinical Trial registration: Registrar: ClinicalTrials.gov Website: www.clinicaltrials.gov Registration Numbers: NCT00001456 and NCT00084305.

Genotype-Phenotype Correlation of Hereditary Erythrocytosis Mutations, a single center experience.

Hereditary erythrocytosis is associated with high oxygen affinity hemoglobin variants (HOAs), 2,3-bisphosphoglycerate deficiency and abnormalities in EPOR and the oxygen-sensing pathway proteins PHD, HIF2α, and VHL. Our laboratory has 40 years of experience with hemoglobin disorder testing and we have characterized HOAs using varied protein and molecular techniques including functional assessment by p50 analysis. In addition, we have more recently commenced adding the assessment of clinically relevant regions of the VHL, BPGM, EPOR, EGLN1 (PHD2), and EPAS1 (HIF2A) genes in a more comprehensive hereditary erythrocytosis panel of tests. Review of our experience confirms a wide spectrum of alterations associated with erythrocytosis which we have correlated with phenotypic and clinical features. Through generic hemoglobinopathy testing we have identified 762 patients with 81 distinct HOA Hb variants (61 ß, 20 α), including 12 that were first identified by our laboratory. Of the 1192 cases received for an evaluation specific for hereditary erythrocytosis, approximately 12% had reportable alterations: 85 pathogenic/likely pathogenic mutations and 58 variants of unknown significance. Many have not been previously reported. Correlation with clinical and phenotypic data supports an algorithmic approach to guide economical evaluation; although, testing is expanded if the suspected causes are negative or of uncertain significance. Clinical features are similar and range from asymptomatic to recurrent headaches, fatigue, restless legs, chest pain, exertional dyspnea and thrombotic episodes. Many patients were chronically phlebotomized with reported relief of symptoms. This article is protected by copyright. All rights reserved.

Factor IX Gene (F9) Genotyping Trends and Spectrum of Mutations Identified: A Reference Laboratory Experience.

In hemophilia B (HB), factor IX gene (F9) genotyping is used for molecular confirmation of affected individuals, for carrier testing, to facilitate the identification of those at risk for anaphylaxis/inhibitors (associated with large deletions), and to assist in assigning disease severity. Owing to test costs, optimal test utilization involves pre/post-test counseling and appropriate patient and test selection (e.g., mutation screening [F9MS] vs. known mutation [F9KM] testing). This article aims to review the trends and outcomes of F9-genotyping orders and describe the spectrum of variants identified in a sample of individuals in our reference laboratory. We performed a retrospective review of consecutive orders submitted to the Special Coagulation DNA Diagnostic Laboratory, Mayo Clinic, between 2012 and 2015. A total of 133 orders (38%) were identified for men: 118 (88%) were F9MS and 15 (12%) were F9KM. Thirteen orders (10%) were cancelled. A total of 209 orders were identified for women: 178 (85%) were F9MS and 31 (15%) were F9KM. Thirty-seven orders (18%) were cancelled and 30% of the tests performed yielded negative results. A total of 164 samples (47%) were received without clinical information. Seventeen previously unreported variants were identified. F9 genotyping provides useful information for HB management; however, 18% of our orders were cancelled and almost half were received without relevant clinical information, thus reaffirming the need for ongoing scrutiny of submitted orders. Optimal patient and test selection is important as is the accurate interpretation of variants identified. Most of the pathogenic variants identified were point mutations, with very few large deletions, consistent with the literature.

Hermansky-Pudlak syndrome subtype 5 (HPS-5) novel mutation in a 65 year-old with oculocutaneous hypopigmentation and mild bleeding diathesis: The importance of recognizing a subtle phenotype.

Hermansky-Pudlak syndrome (HPS) - characterized by the distinct clinical phenotypes of both oculocutaneous albinism and mild bleeding diathesis-is caused by mutations in genes that have crucial roles in the assembly of cellular organelles (skin melanosomes, platelet delta [dense] granules, lung lamellar bodies, and cytotoxic T-cell lymphocyte granules). Immunodeficiency, pulmonary fibrosis and granulomatous colitis are associated with some, but not all subtypes of HPS, with varying degrees of clinical severity. We describe a patient diagnosed with platelet dense granule storage pool deficiency (DG-SPD) at age 38 years after he presented with spontaneous intracranial hemorrhage. His mild oculocutaneous hypopigmentation was subtle. In the following 27 years, he did not develop severe bleeding nor pulmonary or gastrointestinal complications. A novel homozygous c.1960A>T; p.Lys654* mutation in the HPS-5 protein gene (HPS5) was identified through next generation sequencing, (NGS) which is consistent with the patient's clinical and laboratory phenotypes. This case underscores the importance of recognizing the mild clinical phenotype of HPS-5 and utilization of both laboratory and molecular testing for diagnosis, prognostication, and surveillance for end organ damage in patients affected with HPS.

Practice patterns in the diagnosis of inherited platelet disorders within a single institution.

: The diagnosis of inherited platelet disorders (IPDs) is challenging with variable diagnostic practices existing between institutions. To determine patterns and utility of diagnostic testing practices for IPDs within a single institution, a retrospective cohort study was performed. Records of 50 patients (50% women), median age 32 years (1 day to 81 years) were analyzed. In total, 28 (53%) had a positive International Society of Thrombosis and Hemostasis Bleeding Assessment Tool score. Test-ordering patterns were highly variable. All patients had platelet morphology analysis by light microscopy. In total, 42 (84%) underwent light transmission aggregometry, 43 (86%) platelet function analyzer, 37 (74%) platelet electron microscopy, 25 (50%) flow cytometry, and 15 (30%) genetic testing. Platelet function analyzer and light transmission aggregometry were always used as first-order tests, followed by platelet transmission electron microscopy and flow cytometry (81 and 84%, respectively). Genetic testing was obtained up front in five cases (33% of orders), mostly in patients with syndromic thrombocytopenia or in the setting of a known genetic disorder. Test-ordering practices did not adhere to published algorithms. Even within a single institution, great heterogeneity exists in the testing approach to IPDs. Although, a large proportion of cases were studied with platelet transmission electron microscopy and flow cytometry, standard platelet assays established the diagnosis in a great majority. Standardization of testing practices, first beginning at the institutional level is a much needed step forward.

Clinical and laboratory characteristics in congenital ANKRD26 mutation-associated thrombocytopenia: A detailed phenotypic study of a family.

The clinical and laboratory characteristics of patients with non-syndromic, autosomal dominant thrombocytopenia secondary to germ line ANKRD26 mutations appear to be heterogeneous. Except for a targeted molecular genotyping approach, there is no distinct clinical or laboratory phenotype that has been specifically associated with this particular gene mutation. Such heterogeneity could be due to variations in mutation and genetic background in different families. To understand the phenotypic heterogeneity, we thoroughly studied one affected family using the International Society for Thrombosis and Haemostasis bleeding assessment tool and both clinically validated standard and esoteric platelet testing (electron microscopy (EM) and flow cytometry). We found that decreased platelet aggregation with arachidonic acid and epinephrine agonists was common in affected family members. EM studies demonstrated persistent borderline low mean dense granules per platelet, decreased alpha granules and an increased canalicular network pattern in all affected members. Since these characteristics are subtle or non-pathognomonic, molecular testing for ANKRD26 mutation remains the most reliable test to render a diagnosis and should be considered when evaluating a patient or family with congenital thrombocytopenia, particularly if there is a history of myeloid neoplasms.

A Novel ß-Globin Chain Hemoglobin Variant, Hb Allentown [ß137(H15)Val→Trp (GTG>TGG) HBB: c.412_413delinsTG, p.Val138Trp], Associated with Low Oxygen Saturation, Intermittent Aplastic Crises and Splenomegaly.

Hemoglobin (Hb) variants may be associated with low oxygen saturation and exacerbated episodes of anemia from common stressors such as viral infections. These attributes frequently cause increased clinical concern and unnecessary and expensive testing if not considered early in the evaluation of the patient. Some clinically significant Hb variants result in a normal Hb electrophoresis result, which can be method-dependent. Herein we describe a patient with low oxygen saturation and a history of hemolytic anemia who was subsequently found to carry a novel, unstable ß-globin variant that we have named Hb Allentown [ß137(H15)Val→Trp (GTG>TGG) HBB: c.412_413delinsTG, p.Val138Trp] for the place of identification of the variant. Hb Allentown is formed by a rare double nucleotide substitution within the same codon. Additionally, positive identification of rare Hb variants characterized by a single method is discouraged, as the Hb variant was misclassified as Hb S-South End or ß6(A3)Glu→Val;ß132(H10)Lys→Asn (HBB: c.[20A > T;399A > C]) by the initial laboratory.