Efficacy and safety in patients with haemophilia A switching to octocog alfa (BAY 81-8973): Final results of the global real-world study, TAURUS.

OBJECTIVES: To report the final results of the 2-year TAURUS study, assessing weekly prophylaxis dosing regimens of octocog alfa (Kovaltry®/BAY 81-8973) used in standard clinical practice in patients with moderate-to-severe haemophilia A. METHODS: TAURUS (NCT02830477) is a phase 4, multinational, prospective, non-interventional, single-arm study in patients of any age with moderate or severe haemophilia A (≤5% factor [F]VIII activity). TAURUS was designed to primarily investigate weekly prophylaxis dosing regimens used in standard clinical practice. Annualised bleeding rates (ABRs), treatment satisfaction and adherence, and safety were also assessed. RESULTS: Of 302 patients included in the full analysis set, 84.4% (n = 255) maintained their octocog alfa prophylaxis baseline regimen throughout the study, with a majority of patients (76.5%, n = 231) on two times or three times weekly regimens at the end of the observation period (≥1-≤2 years). ABRs, treatment satisfaction, and adherence remained stable during the observation period. Octocog alfa was well tolerated and there were no new or unexpected adverse events. CONCLUSIONS: These data show that a smooth transition is observed when switching to octocog alfa from a previous FVIII treatment, with no safety issues and stable bleeding rates in a real-world setting of patients with moderate-to-severe haemophilia A.

Patient preferences for gene therapy in haemophilia: Results from the PAVING threshold technique survey.

OBJECTIVES: The aim of the Patient preferences to Assess Value IN Gene therapies (PAVING) study was to investigate trade-offs that adult Belgian people with haemophilia (PWH) A and B are willing to make when choosing between prophylactic factor replacement therapy (PFRT) and gene therapy. METHODS: The threshold technique was used to quantify the minimum acceptable benefit (MAB) of a switch from PFRT to gene therapy in terms of 'Annual bleeding rate' (ABR), 'Chance to stop prophylaxis' (STOP), and 'Quality of life' (QOL). The design was supported by stakeholder involvement and included an educational tool on gene therapy. Threshold intervals were analysed using interval regression models in Stata 16. RESULTS: A total of 117 PWH completed the survey. Mean thresholds were identified for all benefits, but substantial preference heterogeneity was observed; especially for the STOP thresholds, where the distribution of preferences was bimodal. Time spent on the educational tool and residence were found to impact MAB thresholds. The most accepted (88% of PWH) gene therapy profile investigated in this study comprised of zero bleeds per year (vs. six for PFRT), 90% chance to stop prophylaxis, no impact on QoL, and 10 years of follow-up on side effects (vs. 30 for PFRT). CONCLUSIONS: Results from this study proved the value of educating patients on novel treatments. Moreover, preference heterogeneity for novel treatments was confirmed in this study. In gene therapy decision-making, preference heterogeneity and the impact of patient education on acceptance should be considered.

BAY 81-8973 prophylaxis and pharmacokinetics in haemophilia A: Interim results from the TAURUS study.

OBJECTIVES: To report interim data from TAURUS, a study assessing real-world prophylactic treatment with unmodified, full-length recombinant FVIII BAY 81-8973 (Kovaltry® ; Bayer) indicated for haemophilia A. METHODS: TAURUS (NCT02830477) is an international, open-label, prospective, non-interventional, single-arm study with a one-year observation period (target N = 350). Patients have moderate or severe haemophilia A (FVIII ≤5% or ≤1%) and ≥50 exposure days to any FVIII product. Clinician- and patient-reported outcomes are captured on previous product use, changes in prophylaxis dose and dosing frequency, FVIII consumption, reported bleeding rates, treatment satisfaction and adherence, pharmacokinetic (PK) data (if available) and safety data. RESULTS: At cut-off, baseline data were available from 160 patients (89 had ≥6 months of follow-up data). Most patients had severe haemophilia A (85%), infused BAY 81-8973 ≥ 3×/wk (59%) and experienced a median number of total bleeds of 2.0 (non-annualised; 246 days median documentation period). Good levels of treatment satisfaction (Hemo-SATA,P ) and adherence (VERITAS-Pro) were maintained. TAURUS demonstrated a favourable PK profile of BAY 81-8973 in comparison with other standard half-life rFVIIIs and supported the WAPPS PopPK model. No patients developed inhibitors. CONCLUSIONS: TAURUS data demonstrate effective prophylaxis with BAY 81-8973 in the real world without compromising patient satisfaction or adherence.

Automated RBC exchange compared to manual exchange transfusion for children with sickle cell disease is cost-effective and reduces iron overload.

BACKGROUND: Chronic transfusion in sickle cell disease (SCD) remains the gold standard therapy for stroke prevention and for patients with severe disease despite adequate hydroxyurea treatment. The aim of our study was to assess the safety and efficacy of automated red blood cell exchange (aRBX) in patients with SCD previously treated with manual exchange transfusion (MET). Costs related to transfusion and chelation overtime were evaluated. STUDY DESIGN AND METHODS: Beginning in January 2012, children with SCD who weighed 30 kg or more on MET could switch to aRBX. Clinical, biological, and procedures' data, including costs, were recorded for the last 6 months on MET and compared to those after the first and the second year on aRBX. RESULTS: Ten patients switched from MET to aRBX at a median age of 11.8 years. After the switch, median hemoglobin S (HbS) increased significantly (33.5% on MET compared to 45% on aRBX; p < 0.001) but remained in the target values for all patients. Median ferritin decreased significantly (663.3 µg/L on MET compared to 126.8 µg/L on aRBX; p < 0.001) and intervals between procedures were significantly longer. The requirements of red blood cells (RBCs)/kg/year were not different on MET (0.88 unit/kg/year) than during the second year on aRBX (1.07 unit/kg/year; p = NS). MET costs were similar compared to aRBX since chelation was stopped in previously treated patients. CONCLUSION: Erythrocytapheresis reduces iron overload and allows a longer interval between procedures without a higher RBC requirement from the second year on aRBX. The cost did not increase as estimated in our Belgian Health Care System.

Different profile of thrombin generation in children with acute lymphoblastic leukaemia treated with native or pegylated asparaginase: A cohort study.

BACKGROUND: Asparaginase (Asp) and corticosteroid (CS) treatment in patients with acute lymphoblastic leukaemia (ALL) is associated with an increased risk of thrombotic events. OBJECTIVE: Characterization of global haemostatic phenotypes of patients with ALL during Asp therapy. PROCEDURE: Thrombin generation (TG) was monitored in platelet-poor plasma of 56 children treated for a B lineage ALL (36 with native, 20 with PEG Asp) using 1 pM tissue factor and 4 µM phospholipids, with and without thrombomodulin. Protein C activity (PC), free protein S (PS), antithrombin (AT) and fibrinogen levels were also measured. RESULTS: Elevated endogenous thrombin potential (ETP) and peak of TG were noted at diagnosis, throughout the Induction phase and Late Intensification but was significantly less for PEG than for native Asp (P < 0.001), while age, sex, type of corticosteroid during Induction and molecular response had no significant effect. The reduction of ETP after addition of thrombomodulin was significantly lower in ALL children compared with that in controls, suggesting impairment in PS/PC pathway. Three patients experienced thrombosis: two treated with native and one with PEG Asp. The two patients with native Asp had, at the time of thrombosis, a prothrombotic profile. CONCLUSIONS: Treatment with Asp, in combination with CS, enhances TG in children with ALL, more significantly with native than PEG Asp, which is present early at diagnosis, persists during Induction and reappears during Late Intensification. This is consistent with the high incidence of thrombotic events described during these phases of therapy. The less pronounced effect of PEG Asp remains to be elucidated.

Survival among children and adults with sickle cell disease in Belgium: Benefit from hydroxyurea treatment.

OBJECTIVE: To evaluate the survival of patients with sickle cell disease (SCD) recorded in the Belgian SCD Registry and to assess the impact of disease-modifying treatments (DMT). METHOD: The Registry created in 2008 included patients of eight centers. All available data in 2008 were retrospectively encoded in the database. After 2008 and until 2012, all data were recorded prospectively for already registered patients as well as newly diagnosed subjects. Data were registered from neonatal screening or from diagnosis (first contact) until last follow-up or death. Data included diagnosis, demography, and outcome data. RESULTS: We collected data from 469 patients over a 5,110 patient years (PY) follow-up period. The global mortality rate was low (0.25/100 PY), although 13 patients died (2.8%) and was similar between children, adolescents (10-18 years), and young adults (P = 0.76). Out of the cohort, 185 patients received hydroxyurea at last follow-up (median duration of treatment: 10.3 years), 90 underwent hematopoietic stem cell transplantation (HSCT), 24 were chronically transfused, and 170 had never had any DMT. Hydroxyurea showed significant benefit on patients outcome as reflected by a lower mortality rate compared to transplanted individuals or people without DMT (0.14, 0.36, and 0.38 per 100 PY, respectively) and by higher Kaplan-Meier estimates of 15 year survival (99.4%) compared to HSCT (93.8%; P = 0.01) or no DMT groups (95.4%; P = 0.04). CONCLUSION: SCD mortality in Belgium is low with no increase observed in young adults. Patients treated with hydroxyurea demonstrate a significant benefit in survival when compared to those without DMT or transplanted.

SARS-CoV-2 Infection in Children Less Than Forty Days Hospitalized in Belgium Between 2020 and 2022.

Our study aimed to assess the severity of severe acute respiratory syndrome coronavirus 2 infection in hospitalized infants under 40 days old, across 21 Belgian hospitals between 2020 and 2022. Of the 365 infants studied, 14.2% needed respiratory support. The median hospital stay was 3 days (interquartile range, 2-4), and there were no deaths. Infection severity was similar during the Omicron and Alpha/Delta periods.

Antibody deficiency due to a missense mutation in CD19 demonstrates the importance of the conserved tryptophan 41 in immunoglobulin superfamily domain formation.

Immunoglobulin superfamily (IgSF) domains are conserved structures present in many proteins in eukaryotes and prokaryotes. These domains are well-capable of facilitating sequence variation, which is most clearly illustrated by the variable regions in immunoglobulins (Igs) and T cell receptors (TRs). We studied an antibody-deficient patient suffering from recurrent respiratory infections and with impaired antibody responses to vaccinations. Patient's B cells showed impaired Ca(2+) influx upon stimulation with anti-IgM and lacked detectable CD19 membrane expression. CD19 sequence analysis revealed a homozygous missense mutation resulting in a tryptophan to cystein (W52C) amino acid change. The affected tryptophan is CONSERVED-TRP 41 located on the C-strand of the first extracellular IgSF domain of CD19 and was found to be highly conserved, not only in mammalian CD19 proteins, but in nearly all characterized IgSF domains. Furthermore, the tryptophan is present in all variable domains in Ig and TR and was not mutated in 117 Ig class-switched transcripts of B cells from controls, despite an overall 10% amino acid change frequency. In vitro complementation studies and CD19 western blotting of patient's B cells demonstrated that the mutated protein remained immaturely glycosylated. This first missense mutation resulting in a CD19 deficiency demonstrates the crucial role of a highly conserved tryptophan in proper folding or stability of IgSF domains.

Thrombin generation reveals high procoagulant potential in the plasma of sickle cell disease children.

Changes in several components of the clotting system are well documented in sickle cell disease (SCD) patients. However, whether the global hemostatic potential of these patients is altered is still unclear. Calibrated automated thrombogram(®) method of thrombin generation (TG) was used to characterize the hemostatic potential of 83 SCD children (75 SS, 6 SC, and 2 Sß (thal)) at steady-state as compared with 50 controls of the same range of age. TG was triggered using 1 pM tissue factor and 4 µM phospholipids with and without thrombomodulin. Thirteen SCD children were also evaluated during vaso-occlusive crisis. Protein C activity, free protein S and D-dimers levels were measured in parallel. SCD patients showed higher rates of thrombin formation, higher thrombin peak height (with and without thrombomodulin), and higher endogenous thrombin potential (ETP) than controls in the presence of thrombomodulin. Reduction of ETP (RETP) in the presence of thrombomodulin was lower in SCD group compared with controls and correlated both with protein C and protein S levels. ETP, RETP, peak height, and velocity index of TG correlated with D-dimers. Compound heterozygous patients showed an intermediate hemostatic phenotype at steady-state. No significant difference was observed when comparing TG parameters during vaso-occlusive crisis to those obtained at steady-state in the same patients. The global hemostatic potential is increased and reflects the hypercoagulable state of SCD patients even at steady-state. The relevance of this finding with respect to the risk of thrombotic complications of the disease needs further investigation.

Osteoid Osteoma: A Unique Presentation in a Child's Lesser Toe.

INTRODUCTION: Osteoid osteoma is an uncommon, small, benign, self-limiting, and usually painful tumor of the skeleton. Diagnosis can be straightforward if seen in the usual locations as the femur and the tibia in young adults, who present with nocturnal pain, alleviated by salicylates. The diagnosis can be more challenging in the spine, pelvis, hand, or feet. Case Report. We report the case of an 11-year-old boy who was treated symptomatically for a painful toe since 10 months, without a definitive diagnosis. X-ray, MRI, and scintigraphy, along with the typical nocturnal pain and swelling of the toe, suggested an osteoid osteoma, confirmed by histology after excisional biopsy of the lesion. CONCLUSION: Osteoid osteoma should always be included in the differential diagnosis when it comes to nocturnal pain without systemic signs, even in unusual places in children. The awareness should lead to a prompt diagnosis and treatment.

Diagnosis of respiratory syncytial virus and influenza A and B with cobas® Liat® from nasopharyngeal aspirations in pediatrics.

The cobas® Liat® Influenza A/B and respiratory syncytial virus assay was tested on nasopharyngeal aspirates. The resolution of invalid samples was performed using a preanalytical step. cobas® Liat® can be used on nasopharyngeal aspirates with a preanalytical processing step, with a slightly diminished performances in detecting respiratory syncytial virus but not for influenza.

Serum calprotectin (S100A8/A9): a promising biomarker in diagnosis and follow-up in different subgroups of juvenile idiopathic arthritis.

INTRODUCTION: In the management of juvenile idiopathic arthritis (JIA), there is a lack of diagnostic and prognostic biomarkers. This study assesses the use of serum calprotectin (sCal) as a marker to monitor disease activity, and as a classification and prognosis tool of response to treatment or risk of flares in patients with JIA. METHODS: Eighty-one patients with JIA from the CAP48 multicentric cohort were included in this study, as well as 11 non-paediatric healthy controls. An ELISA method was used to quantify sCal with a commercial kit. RESULTS: Patients with an active disease compared with healthy controls and with patients with inactive disease showed an eightfold and a twofold increased level of sCal, respectively. sCal was found to be correlated with the C-reactive protein (CRP) and even more strongly with the erythrocyte sedimentation rate. Evolution of DAS28 scores correlated well with evolution of sCal, as opposed to evolution of CRP. With regard to CRP, sCal could differentiate forms with active oligoarthritis from polyarthritis and systemic forms. However, sCal brought an added value compared with the CRP as a prognosis marker. Indeed, patients with active disease and reaching minimal disease activity (according to Juvenile Arthritis Disease Activity Score) at 6 months following the test had higher sCal levels, while patients with inactive disease had higher sCal levels if a flare was observed up to 3-9 months following the test. CONCLUSIONS: This study confirms the potential uses of sCal as a biomarker in the diagnosis and follow-up of JIA.

Etanercept improves linear growth and bone mass acquisition in MTX-resistant polyarticular-course juvenile idiopathic arthritis.

OBJECTIVES: Chronic inflammation in juvenile idiopathic arthritis interferes with linear growth and bone mass acquisition. We prospectively evaluated and compared linear growth and evolution of bone mass acquisition and body composition in MTX-resistant polyarticular-course JIA (polyJIA) patients started on etanercept and in recently diagnosed polyJIA patients started on MTX monotherapy. METHODS: Sixteen MTX-resistant polyJIA patients were given add-on etanercept, eight recently diagnosed polyJIA patients were started on MTX. Patients were evaluated at baseline and at 1, 6, 12 and 18 months with respect to disease activity, linear growth, BMD and body composition. RESULTS: Baseline patient and disease characteristics were similar in both groups. Clinical disease activity (Pediatric ACR30) was equally well controlled in both groups. Growth velocity increased significantly allowing catch-up growth in the etanercept + MTX group only. BMD (lumbar spine Z-score) improved significantly in both groups. A significant increase of bone mineral content and lean:fat mass ratio was seen in the etanercept + MTX group, but not in the MTX group. CONCLUSION: Clinical control of disease activity by etanercept in MTX-refractory polyJIA is associated with rapidly instituted catch-up growth and improvement of bone mineralization and body composition. In recently diagnosed polyJIA patients treated with MTX the relation between clinical response and these parameters was less evident. Preliminary data on serum IL-6 and osteoprotegerin levels indicate that the beneficial effects seen with etanercept therapy may be related to its control of systemic IL-6 production and enhancement of osteoblast activity.

Sickle cell disease from Africa to Belgium, from neonatal screening to clinical management.

AIM: To describe the severity of sickle cell disease (SCD) in newborns in Belgium and evaluate the impact of neonatal screening (NS) on clinical outcome. METHODS: Universal NS of umbilical cord blood for hemoglobinopathy was progressively deployed in Brussels and Liège starting in 1994. No particular population was targeted. Samples were analyzed initially using the isoelectric focusing technique and since 2008 the capillary electrophoresis technique. If a hemoglobin variant was suspected, further analysis was carried out using high performance liquid chromatography. Children presenting major hemoglobinopathy, especially SCD, were referred to a specialized centre for comprehensive management. Preventive measures included antipneumococcal prophylaxis immunization/antibiotic therapy, parental training to recognize severe anemia and splenic sequestration, and transcranial ultrasound recording for early detection of intracranial stenosis. A database was set up in Belgium to collect clinical and laboratory data including parental phenotype, diagnostic technique (neonatal screening or not), major clinical events (episodes of dactylitis, acute chest syndrome, severe anemia, infection, etc), number and duration of required hospitalizations, and treatment used. RESULTS: Screening of 222352 newborns in maternity units in Brussels led to diagnosis of SCD in 145 patients, Adequate data for analysis of clinical outcome was available for 96 of these children born before 2007. Median age in the study group was 4.2 years and the total duration of follow-up was 510 years. Most cases occurred in families from the Democratic Republic of Congo. (64/96 patients; 66.7%) and involved homozygous hemoglobin S disease (80/96 patients; 83.3%). Twenty-seven percent of patients (26/96) presented no severe clinical events during the study (17 SS, median age 2,1 years (0-13.1 years). Conversely 33% presented an episode of dactylitis and 47.9% (46/96) presented recurrent vasoocclusive crises. Severe anemia was observed in 39.6% (38/96) of cases. Six patients (6.3%) developed septicemia despite prophylactic antibiotic therapy and anti-pneumococcal immunization using heptavalent conjugate vaccine and polysaccharide vaccine, No penicillin-resistant strains were observed. The incidence of stroke was 2.1% (3/96). Two patients presenting homozygous hemoglobin S disease died due to septicemia due to non-compliance with antibiotic therapy in one case and severe anemia in one case. All episodes of septicemia and both deaths occurred at the beginning of the NS program. Hydroxyurea therapy was used in 30 patients (31.2%) including 7 in whom transcranial Doppler depicted blood flow abnormalities and 8 in whom allogeneic bone marrow transplantation was performed. CONCLUSIONS: Sickle cell disease is still associated with high morbidity and mortality but clinical care has improved and no death has occurred in the last 10 years. NS is an effective tool for early detection and management of SCD. Neonates with SCD diagnosed by NS in Belgium presented severe manifestations, but clinical outcomes were improved by comprehensive management.

Is There Any Improvement of the Coagulation Imbalance in Sickle Cell Disease after Hematopoietic Stem Cell Transplantation?

Several components of the clotting system are modified towards hypercoagulability in sickle cell disease (SCD). To date, hematopoietic stem cell transplantation (HSCT) is the only validated curative treatment of SCD. Here, we investigated the changes in the hemostatic potential of SCD children who've received a successful HSCT. Seventeen children with severe SCD were enrolled in the study. Thrombin generation (TG) was performed on citrated platelet-poor plasma, obtained before and 3, 6, 9, 12 and 15 months after HSCT. TG was triggered using 1 pM tissue factor and 4 µM phospholipids with or without thrombomodulin (TM). Before the HSCT, SCD children showed a higher endogenous thrombin potential (ETP), higher peak, higher velocity and shorter time-to-peak of TG than the normal controls (NC). ETP did not significantly change following the HSCT. However, the peak, velocity and time-to-peak of TG reversed to normal ranges from 3 months post-HSCT and remained so up to 15 months post-HSCT. The reduction of ETP after the addition of thrombomodulin (RETP) was dramatically reduced in SCD children before HSCT as compared with the NC. A partial reversal of RETP was observed from 3 months through 15 months post-HSCT. No statistical difference was observed for patient age or donor hemoglobinopathy status. In summary, successful HSCT improves the kinetics of TG but not the total thrombin capacity in SCD children.

Neonatal Screening for Sickle Cell Disease in Belgium for More than 20 Years: An Experience for Comprehensive Care Improvement.

Our previous results reported that compared to sickle cell patients who were not screened at birth, those who benefited from it had a lower incidence of a first bacteremia and a reduced number and days of hospitalizations. In this context, this article reviews the Belgian experience on neonatal screening for sickle cell disease (SCD). It gives an update on the two regional neonatal screening programs for SCD in Belgium and their impact on initiatives to improve clinical care for sickle cell patients. Neonatal screening in Brussels and Liège Regions began in 1994 and 2002, respectively. Compiled results for the 2009 to 2017 period demonstrated a birth prevalence of sickle cell disorder above 1:2000. In parallel, to improve clinical care, (1) a committee of health care providers dedicated to non-malignant hematological diseases has been created within the Belgian Haematology Society; (2) a clinical registry was implemented in 2008 and has been updated in 2018; (3) a plan of action has been proposed to the Belgian national health authority. To date, neonatal screening is not integrated into the respective Belgian regional neonatal screening programs, the ongoing initiatives in Brussels and Liège Regions are not any further funded and better management of the disease through the implementation of specific actions is not yet perceived as a public health priority in Belgium.

Neonatal screening improves sickle cell disease clinical outcome in Belgium.

Objectives To compare the outcomes of sickle cell disease patients diagnosed through neonatal screening with those who were not. Methods In an observational multicenter study in Belgium, 167 screened and 93 unscreened sickle cell disease patients were analyzed for a total of 1116 and 958 patient-years of follow-up, respectively. Both groups were compared with propensity score analysis, with patients matched on three covariates (gender, genotype, and central Africa origin). Bonferroni correction was applied for all comparisons. Results Kaplan-Meier estimates of survival without bacteremia were significantly higher in the screened group than the unscreened group (94.47%; [95% CI, 88.64-97.36%] versus 83.78% [95% CI, 72.27-90.42%]), p = 0.032. Non-significant differences between both groups were reported for survival without acute chest syndrome, acute anemia, cerebral complication, severe infection, and vaso-occlusive crisis. Significantly lower hospitalization rate and days per 100 patient-years were observed in the screened compared with the unscreened group (0.27 vs. 0.63 and 1.25 vs. 2.82, p = 0.0006 and <0.0001). Conclusion These data confirm the benefit of a neonatal screening programme in reducing bacteremia and hospitalization.

Imaging of Juvenile Idiopathic Arthritis.

Juvenile idiopathic arthritis is an umbrella term covering several distinct categories that share common features. The European League Against Rheumatism and the Pediatric Rheumatology European Society have published a consensus article with recommendations to guide radiologists and clinicians in choosing the best imaging technique for each particular clinical setting. A reproducible, accurate, validated, and long-established scoring system to use in everyday practice for monitoring and predicting long-term response to therapy is still to be developed on MR imaging for each joint.

GCMB mutation in familial isolated hypoparathyroidism with residual secretion of parathyroid hormone.

Isolated hypoparathyroidism is an uncommon metabolic disorder characterized by hypocalcemia and hyperphosphatemia, with absent or low levels of PTH. It may present as an apparently sporadic disorder or may be transmitted in families as a genetic trait. Mutations of the calcium-sensing receptor gene and of the preproPTH gene have been reported in occasional cases, and a mutation of the parathyroid-specific transcription factor GCMB gene has been reported in one familial case. We report a second family with isolated hypoparathyroidism and a GCMB mutation. The patients were two siblings from asymptomatic, first-cousin parents, indicating autosomal recessive inheritance. The mutation consisted of the substitution of a glycine residue with a serine at position 63 (G63S) in the DNA-binding GCM domain of GCMB. Functional studies in transfected cells showed that the mutation caused loss of GCMB function, as it abolished transactivation capacity, despite normal subcellular localization, protein stability, and DNA-binding specificity. Contrary to the previously reported family, our patients displayed low but clearly detectable levels of PTH in plasma. This residual hormone secretion probably results from a very small residual activity of the G63S mutant GCMB.