The Grndad Registry: Contemporary Natural History Data and an Analysis of Real-World Patterns of Use and Limitations of Disease Modifying Therapy in Adults with SCD

Incremental improvement in care for children with sickle cell disease (SCD), arising from government-funded research over the last 4 decades, resulted in a dramatically reduced childhood mortality. However, the impact of iterative research and disease modifying therapy (DMT) on adults with SCD has not been as strong. Until now, there has been no coordinated, longitudinal, generalizable, natural history study of SCD that allowed for an assessment of the contemporary adult population.

Here, we describe demographics at enrollment and cross-sectional clinical characteristics of 570 adults with SCD (SCA, homozygous HbSS or HbSb⁰ N=387, 68%, and compound heterozygous SCD variant, HbSC or HbSb⁺ N=183, 32%, Table I) on whom we have evaluable data. These data are from the multi-site REDCap-based prospective Globin Research Network for Data and Discovery (GRNDaD) registry, comprising 11 centers with over 1100 consented adults and children. The objective of this work was to evaluate the cohort at year of entry, including the use and clinical associations with DMT, and to explore indicators of disease progression as patients age.

16% of adults with SCA and 9.6% with variant disease stroke; 60.9% of adults with SCA and 41% with variant disease had a history of acute chest syndrome. Albuminuria was prevalent in both SCA (39.5%) and variant disease (19.4%). 185 adults (185/387, 47.8%) with SCA, previously referred for symptoms in clinic, had recorded tricuspid regurgitant jet velocity measurements, with a significantly abnormal result (>2.7 m/s), in 92 (92/185, 49.7%).

At enrollment, 45% of adults with SCA (175/387) and 14% of adults with variant disease (25/183) were on hydroxyurea (HU); 20.4% of adults with SCA were on chronic transfusions (79/387) compared with 7% of adults with variant disease (13/183). One third of all adults with SCA were not on or were not consistently on DMT, and had laboratory evidence for increased hemolysis (Table 1).

Adults with SCA who were on HU had a higher MCV and higher HbF than other treatment states (Table 1). However, only 34% (60/175) of adults with SCA on HU were at maximally tolerated dose (MTD), per guideline-based recommendations, i.e. ANC ≤4.0 x10⁹/L. On HU, those in the lowest quartile for ANC (<3.2 x10⁹/L) were older (mean age 35.9 years (95% Confidence Limit (CL) 32.5-39.3) vs. 31.2 (95% CL 28.2 to 34.4) years, P=0.04), had a lower mean reticulocyte count (119 x10⁹/L (95% CL 76-162) vs. 203 (95% CL 129-278), P=0.05), and a higher mean MCV (104.4 fL (95% CL 100.2-108.7) vs. 92.5 (95% CL 87.2-97.8), P=0.0007), compared to those in the highest quartile for ANC (>5.7 x10⁹/L, N=34), but did not otherwise differ (including mean HbF, which was not measured in a standardized way).

In older adults with SCD (Table 2), fewer people with SCA than with variant disease were >54 years old, (26/387 HbSS, 7%, vs. 34/183, 19%, respectively). The older adult with SCA had a depressed reticulocyte count and a trend towards a higher creatinine.

45% of adults with SCA were on HU, and only a minority were at MTD, highlighting the challenges to optimal long-term therapy in chronic illness. Those patients not stably on DMT had laboratory evidence for worse anemia and hemolysis, without an evident increase in hospital admissions, perhaps due to a hyper hemolytic phenotype. Despite a more intensive regimen, SCA patients on transfusions had a higher Hgb but did not have hemolysis labs that differed from SCA patients on HU. Further, there was no difference in hospitalizations amongst treatments for SCA, although a decrease in hospitalizations was detectable in variant disease (Table 1). Successful use of DMTs in SCA was challenging even in academic centers, and there was evidence for ongoing hemolysis in treated and untreated patients.

These real world data provide useful information about adults (>17 years) with SCD. These data highlight opportunities to improve adherence to therapy (patient-centered) and to prescribing guidelines (provider-centered), and to consider less-burdensome alternatives. Importantly, we found that a large proportion of people with SCA were not on DMT, and with HU often not at MTD. In future, the GRNDaD registry will enable prospective longitudinal real-world analyses of the impact of DMTs and/or newer therapies on clinical outcomes, will enhance quality improvement, and will allow us to more fully explore clinical characteristics, of SCA and variant disease, in the aging adult.