Discrepant Hemophilia A: An Underdiagnosed Disease Entity

Genetic testing for children at risk to be hemophilia carriers

Carriers for hemophilia are at risk for bleeding despite normal or mildly reduced factor 8 or factor 9 activity levels. Genetic testing is necessary to determine carrier status in those at risk and early identification of carriers can inform their bleeding risk. The aims of this single-center retrospective study were to determine the uptake of genetic testing in children at risk to be hemophilia carriers and identify barriers to completion of testing. We identified 64 unique at-risk children assigned female sex at birth under 18 years old, with at least one caregiver participating in a visit between June 2019 and July 2023 with a genetic counselor with expertise in hemophilia. Of all those at risk, 27% (17/64) had undergone genetic testing prior to having genetic counseling at our center, at a median age of 5 years. Of those who had not yet had genetic testing (47/64): insurance prior authorization was initiated for 49% (23/47), testing was completed for 28% (13/47) at a median age of 11 years, and factor activity levels were known or drawn after the visit for 36% (17/47). The primary reason (14/24, 58%) for not initiating insurance prior authorization was not having a known family variant. Because carrier testing for X-linked disorders standardly involves targeted family variant testing rather than full gene testing, increasing the accessibility of carrier testing depends on increasing the accessibility and uptake of genetic testing in affected family members, usually individuals assigned male sex at birth, with a diagnosis of hemophilia. The impact of the decision to pursue genetic testing on current or future family members at risk to be carriers could be included in counseling discussions with individuals with hemophilia and their families.

Comparing one stage, chromogenic assay results and discrepancies with bleeding phenotype and genetic variants in females with hemophilia A

BACKGROUND

Increasing evidence in females with hemophilia A has shown significant bleeding symptoms. Accurate factor (F) VIII activity (FVIII:C) measurement is essential to assign correct diagnosis and severity. Assay discrepancies reported in male patients with hemophilia A are not well studied in females.

OBJECTIVES

Our research sought to assess the association of FVIII:C levels by one-stage versus chromogenic assays and the assay discrepancy with bleeding phenotype and genetic mutation in females with hemophilia A.

METHODS

Data from 64 females with hemophilia A from our center were reviewed with center's institutional review board approval. Descriptive statistics, chi-squared, Fisher's exact, and Bland-Altman plot analysis were applied.

RESULTS

Abnormal International Society on Thrombosis and Haemostasis bleeding assessment tool score was seen in 52% (FVIII:C <40 IU/dL: 72%/73%; FVIII:C ≥40 IU/dL: 41%/45%; by one-stage and chromogenic assays, respectively), more often in adults and postmenarchal patients. Assay discrepancies were present, direct more often than inverse. Based on one assay result only, 11 (17%) patients would have been incorrectly diagnosed and 1 (1.5%) patient would have been assigned incorrect hemophilia severity. No associations of genetic variants with FVIII:C levels and bleeding phenotype were found.

CONCLUSION

Our study emphasizes the importance of evaluating female patients with hemophilia A for bleeding phenotype. Our study is the first to document prevalence of assay discrepancies exclusively in females with hemophilia A, which can lead to inaccurate diagnosis and severity assignment. Future larger, multicenter studies are needed to validate our findings, to help develop recommendations regarding the appropriate use of assays for accurate diagnosis and to further elucidate the association of genetic variants with bleeding phenotype and assay discrepancies.

Evaluation of discrepancy between clot-based and chromogenic factor IX coagulation assays in non-severe hemophilia B patients and identification of the causing mutations

BACKGROUND

Hemophilia B, or Christmas disease, is a hemorrhagic inherited disorder. Previous studies have reported measurement discrepancies in factor VIII activity between clot-based and chromogenic assays in approximately one-third of patients with non-severe hemophilia A. However, similar discrepancies in hemophilia B have been less extensively studied. This research compares clot-based and chromogenic assays in 33 patients with non-severe hemophilia B and investigates the mutations associated with these discrepancies.

METHODS

Citrate and EDTA samples were collected from 33 patients with non-severe hemophilia B at Iran's hemophilia comprehensive care center. Clinical information was also gathered. Both clot-based and chromogenic assays were performed on these patients. DNA was extracted from the EDTA samples for those with discrepancies in the test results, and PCR was conducted to sequence their genes to find mutations.

RESULTS

Among 33 plasma samples from patients with non-severe hemophilia B, 7 showed a measurement discrepancy according to the definition of ISTH (<0.5, >2.0, or an absolute difference >10), which includes both reverse and classic types of discrepancies. In this study, mutations that previously did not show contradictory results now exhibit discrepancies. A difference in classification was observed in 21 % of the patients.

CONCLUSIONS

The findings indicate that the impact of specific mutations varies depending on the assay conditions. In addition to mutations, other factors also play a role in this discrepancy. Both types of assays are essential for the accurate diagnosis and classification of hemophilia B.

Acquired Factor VIII Inhibitors: A Case Study

The physiology of hemostasis is one of high complexity that involves the initiation, amplification, and propagation of the many moving parts of the hemostatic system and its regulatory mechanisms. It is imperative that clinical laboratory professionals have a strong understanding of the many intricacies of the physiology of coagulation and its in vitro testing. An elongated activated partial thromboplastin time can have several causes, and the correct cause must be elucidated in a timely manner for proper treatment. A mixing study with normal pooled plasma should be performed to evaluate for the presence of an inhibitor vs factor deficiency. Factor inhibitors, specifically factor VIII in this case study, should be titered so that the clinician can decide which treatment may work best for the patient. Continued monitoring of factor levels and inhibitor titers should be conducted to follow the resolution or progression of inhibitor presence.

Cryptogenic oozers and bruisers

Bleeding disorders with normal, borderline, or nondiagnostic coagulation tests represent a diagnostic challenge. Disorders of primary hemostasis can be further evaluated by additional platelet function testing modalities, platelet electron microscopy, repeat von Willebrand disease testing, and specialized von Willebrand factor testing beyond the usual initial panel. Secondary hemostasis is further evaluated by coagulation factor assays, and factor XIII assays are used to diagnose disorders of fibrin clot stabilization. Fibrinolytic disorders are particularly difficult to diagnose with current testing options. A significant number of patients remain unclassified after thorough testing; most unclassified patients have a clinically mild bleeding phenotype, and many may have undiagnosed platelet function disorders. High-throughput genetic testing using large gene panels for bleeding disorders may allow diagnosis of a larger number of these patients in the future, but more study is needed. A logical laboratory workup in the context of the clinical setting and with a high level of expertise regarding test interpretation and limitations facilitates a diagnosis for as many patients as possible.