F8 gene dosage defects in atypical patients with severe haemophilia A

F8 gene inversion and duplication cause no obvious hemophilia A phenotype

Hemophilia A (HA, OMIM#306700) is an X-linked recessive bleeding disorder caused by the defects in the F8 gene, which encodes coagulation factor VIII (FVIII). Intron 22 inversion (Inv22) is found in about 45% of patients with severe hemophilia A. Here, we reported a male without obvious hemophilia A phenotype but bearing an inherited segmental variant duplication encompassing F8 as well as Inv22. The duplication was approximately 0.16 Mb and involved from exon 1 to intron 22 of F8. This partial duplication and Inv22 in F8 was first found in the abortion tissue of his older sister with recurrent miscarriage. The genetic testing of his family revealed that his phenotypically normal older sister and mother also had this heterozygous Inv22 and a 0.16 Mb partial duplication of F8, while his father was genotypically normal. The integrity of the F8 gene transcript was verified by sequencing of the adjacent exons at the inversion breakpoint, which explained why this male had no phenotype for hemophilia A. Interestingly, although he had no significant hemophilia A phenotype, the expression of C1QA in his mother, sister, and the male subject was only about half of that in his father and normal population. Our report broadens the mutation spectrum of F8 inversion and duplication and its pathogenicity in hemophilia A.

Prenatal diagnosis for hemophilia A (intron 22 inversion) reveals a rare association with Klinefelter syndrome with diagnostic difficulties in molecular interpretation

Hemophilia A is an X-linked recessive disorder caused by genetic abnormalities in the F8 . Klinefelter syndrome is sex chromosome aneuploidy caused by nondisjunction during meiosis in the germ cells or mitotic cell divisions in the early embryonic cells. We here report an intriguing case of a prenatal diagnosis where a rare association of hemophilia A and Klinefelter syndrome was found in a fetus. This case highlights the diagnostic difficulty where the inverse-PCR for intron 22 inversion defect leading to hemophilia A did not amplify. Indirect molecular testing was done using multiallelic extragenic variable number tandem repeat (VNTR) DXS52 (St14) and polymorphic markers. The interpretation was further complicated by the presence of Klinefelter syndrome. This case highlights the challenges faced when such rare combinations are found during prenatal diagnosis.

Applicability of the Thrombin Generation Test to Evaluate the Hemostatic Status of Hemophilia A Patients in Daily Clinical Practice

Hemophilia A (HA) is a rare bleeding disorder caused by factor VIII (FVIII) deficiency due to various genetic mutations in the F8 gene. The disease severity inversely correlates with the plasma levels of functional FVIII. The treatment of HA patients is based on FVIII replacement therapy, either following a prophylactic or on-demand regime, depending on the severity of the disease at diagnosis and the patient’s clinical manifestations. The hemorrhagic manifestations are widely variable amongst HA patients, who may require monitoring and treatment re-adjustment to minimize bleeding symptoms. Notably, laboratory monitoring of the FVIII activity is difficult due to a lack of sensitivity to various FVIII-related molecules, including non-factor replacement therapies. Hence, patient management is determined mainly based on clinical manifestations and patient–clinician history. Our goal was to validate the ST Genesia^® automated thrombin generation analyzer to quantify the relative hemostatic status in HA patients. We recruited a cohort of HA patients from the Principality of Asturias (Spain), following treatment and at a stable non-bleeding phase. The entire cohort (57 patients) had been comprehensively studied at diagnosis, including FVIII and VWF activity assays and F8 genetic screening, and then clinically monitored until the Thrombin Generation Test (TGT) was performed. All patients were recruited prior to treatment administration, at the maximum time-window following the previous dose. Interestingly, the severe/moderate patients had a similar TGT compared to the mild patients, reflecting the non-bleeding phase of our patient cohort, regardless of the initial diagnosis (i.e., the severity of the disease), treatment regime, and FVIII activity measured at the time of the TGT. Thus, TGT parameters, especially the peak height (Peak), may reflect the actual hemostatic status of a patient more accurately compared to FVIII activity assays, which may be compromised by non-factor replacement therapies. Furthermore, our data supports the utilization of combined TGT variables, together with the severity of patient symptoms, along with the F8 mutation type to augment the prognostic capacity of TGT. The results from this observational study suggest that TGT parameters measured with ST Genesia^® may represent a suitable tool to monitor the hemostatic status of patients requiring a closer follow-up and a tailored therapeutic adjustment, including other hemophilia subtypes or bleeding disorders.

Custom oligonucleotide array-based CGH: a reliable diagnostic tool for detection of exonic copy-number changes in multiple targeted genes

The frequency of disease-related large rearrangements (referred to as copy-number mutations, CNMs) varies among genes, and search for these mutations has an important place in diagnostic strategies. In recent years, CGH method using custom-designed high-density oligonucleotide-based arrays allowed the development of a powerful tool for detection of alterations at the level of exons and made it possible to provide flexibility through the possibility of modeling chips. The aim of our study was to test custom-designed oligonucleotide CGH array in a diagnostic laboratory setting that analyses several genes involved in various genetic diseases, and to compare it with conventional strategies. To this end, we designed a 12-plex CGH array (135k; 135 000 probes/subarray) (Roche Nimblegen) with exonic and intronic oligonucleotide probes covering 26 genes routinely analyzed in the laboratory. We tested control samples with known CNMs and patients for whom genetic causes underlying their disorders were unknown. The contribution of this technique is undeniable. Indeed, it appeared reproducible, reliable and sensitive enough to detect heterozygous single-exon deletions or duplications, complex rearrangements and somatic mosaicism. In addition, it improves reliability of CNM detection and allows determination of boundaries precisely enough to direct targeted sequencing of breakpoints. All of these points, associated with the possibility of a simultaneous analysis of several genes and scalability 'homemade' make it a valuable tool as a new diagnostic approach of CNMs.