Analysis of published data
We have included 12 case reports of hydroxychloroquine-mediated hemolytic anemia in G6PD-deficient COVID-19 patients published during the period of 2020 – 2021. All were men with the mean age of 49.5 ± 18.3 yr. Out of these 12, seven patients were of African Ancestry (58.3%). Seven were diabetic (58.3%), two had hypertension (16.7%), two had cardiac problems (16.7%), three were obese (25%), two had renal problems (16.7%), five were using azithromycin (41.7%), two were on concomitant therapy with contra-indicated medications (sulfa drugs, methylene blue (16.7%). Two patients expired following the therapy. A 54 yr old man from USA expired with Coomb’s negative hemolysis following co-administration of methylene blue along with hydroxychloroquine and azithromycin. A 60 yr old African American man with acute kidney injury, electrolyte abnormalities, high anion gap, metabolic acidosis expired due to severe hemolytic crisis following HCQS therapy. N-acetyl cysteine was reported to be effective in reversing the hemolytic anemia induced by HCQS and sulfa in one patient. Folate was effective in reversing HCQS-mediated hemolysis in one patient. (Table 1)
Subjects with African Ancestry exhibited significant lowering of hemoglobin following HCQS therapy (pre- vs. post-therapy Hb, g/dl: 12.75 ± 1.57 vs. 6.78 ± 0.62, p=0.0008) than those from those with non-African ancestry (pre- vs. post-therapy Hb, g/dl: 13.27 ± 1.51 vs. 9.97 ± 2.34, p=0.04). Diabetics exhibited significant lowering of hemoglobin following HCQS therapy (pre- vs. post-therapy Hb, g/dl: 12.96 ± 0.98 vs. 6.82 ± 0.76, p=0.0007) than non-diabetics (pre- vs. post-therapy Hb, g/dl: 12.88 ± 2.13 vs. 9.13 ± 2.51, p=0.05). (Fig 1)
Multiple Linear regression
We have used African Ancestry, diabetes, hypertension, and use of azithromycin as the input variables and HCQS-induced hemolytic drop in hemoglobin (Hb) as output variable. This additive model suggests that in G6PD-deficient subjects with African ancestry are more prone for developing hemolytic anemia with 2.04 g/dl drop in hemoglobin following HCQS therapy for COVID-19. Diabetics will have 1.51 g/dl drop in hemoglobin. Hypertension and azithromycin have only minor contribution towards inducing hemolytic anemia. MLR model based on these variables explained 53.75% variability in HCQS-induced hemolytic anemia. (Fig 2) The mathematical representation of this model is shown below:

Classification and Regression Tree (CART) model
G6PD deficiency in African Ancestry subjects was found to be the key predictor of HCQS-mediated hemolytic anemia. The second predictor being the diabetes followed by obesity. Hypertension and azithromycin use being the mild contributors. These variables cumulatively explain all the contributors towards HCQS-mediated hemolytic anemia (R2: 1.00). G6PD deficient African Ancestry subjects with diabetes and obesity exhibited maximum drop in hemoglobin following HCQS-therapy (8.6 g/dl). G6PD deficient African Ancestry non-diabetic subjects exhibited maximum drop in hemoglobin when Azithromycin is co-administered concomitantly (7.3 g/dl). The drop in hemoglobin is lowest in subjects of non-African Ancestry without obesity and concomitant use of Azithromycin (2.4 g/dl). (Fig 3)
G6PD variant analysis in our population
We have used Infinium global screening array to identify the G6PD variants in our population, which are likely to be risk factors for HCQS-mediated hemolytic anemia. This array covers 56 G6PD variants. The SNP missing call rate was 0.0025±0.005. Out of the 1215 men screened, 52 had G6PD deficiency. G6PD Mediterranean (n=19) and G6PD Kerala-Kalyan (n=18) are the most common variants identified. G6PD Orissa was observed in six subjects. G6PD Mahidol, G6PD Viangchan /Jammu, G6PD Chatham were observed in two subjects each. G6PD Y70H, G6PD L235F and G6PD Union were observed in one subject each.
In silico studies (Table 2)
G6PD wild
We have used the crystal structure of G6PD (PDB ID: 6E08) as a reference for the wild protein. The NADP interacts with 38G, 40S, 41G, 42D, 43L, 112Y,141A, 142L, 143P, 170E, 199I, 200D, 201H, 246R, 437Y residues. NADP forms 8 hydrogen bonds i.e., one each with 43L, 112Y, 199I; three with 171K, and two with 201H. (Supplementary Fig 1)
G6PD Mediterranean (S188F)
This is predicted to be deleterious by SIFT, Provean and SNAP2 scores. Its position specific evolutionary conservation (PSEP) time is 220 million years suggesting possibly damaging nature. The ligand propensity score is 9. In the S188F, the NADP binding site is devoid of 38G, 200D, and 246R residues. Hence, there is a disruption of the H-bond with 43L and the formation of new bonds with 40S, 72R, 141A, and 147Y.
G6PD Kerala-Kalyan (E317K)
This is predicted to be deleterious by Provean score. Its PSEP time is 361 million years suggesting possibly damaging nature. The ligand propensity score is 0. In the E317K variant, the NADP binding site is devoid of 200D and 246R. This results in the loss of H-bond with 43L and the formation of new H-bonds with 40S, 42D, and 72R.
G6PD Orissa (A44G)
This is predicted to be deleterious by SIFT, Provean and SNAP2 scores. Its PSEP time is 4200 million years suggesting probably damaging nature. It is found to be thermolabile (DG: -3.79 Kcal/mol). In the A44G variant, the NADP binding site is devoid of 199I, 200D, and 246R residues. This resulted in the loss of H-bonds with 43L, 112Y, 199I and the formation of new H- bonds with the 40S, 72R, 142L, and 147Y.
G6PD Mahidol (G163S)
This is predicted to be deleterious by SIFT, Provean and SNAP2 scores. Its PSEP time is 4200 million years suggesting probably damaging nature. The ligand propensity score is 7. In G163S variant, the NADP binding site is devoid of 199I, 200D, and 246R residues. As a result, there is a loss of H-bonds with 43L and 199I and the formation of new H-bonds with 40S, 72R, 142L, and 147Y.
G6PD Viangchan/Jammu (V291M)
This is predicted to be deleterious by SIFT, Provean and SNAP2 scores. Its PSEP time is 4200 million years suggesting probably damaging nature. The ligand propensity score is 2. In the V291M variant, the NADP binding site is devoid of 199I, 200D, 201H, and 246R residues. There is disruption of H-bonds with 199I and 201H and new H-bond formation with 40S, 42D, 47K, 72R, 142L, and 437Y.
G6PD Chatham (A335T)
This is predicted to be deleterious by SIFT and SNAP2. Its PSEP time is 324 million years suggesting possibly damaging nature. Its ligand propensity score is 2. In the A335T variant, the NADP binding site is devoid of 38G, 40S, 112Y, 200D, and 246R residues. As a result, there is disruption of H-bond at 112Y and formation of new H-bonds with 42D, 72R, 141A, 142L, and 147Y.
G6PD Y70H
This is predicted to be deleterious by SIFT, Provean and SNAP2. Its PSEP time is 361 million years suggesting possibly damaging nature. It has high thermolability (DG: -8.17 Kcal/mol). Its ligand propensity score is 9. In the Y70H variant, the catalytic binding site is devoid of 38G, 40S, 41G, 112Y, 141A, 142L, 143P, and 246R residues. This led to the loss of H-bonds with 43L, 112Y, and 199I and the formation of new H-bonds with 47K and 89K residues.
G6PD L235F
This is predicted as neutral variant by SIFT, Provean and SNAP2. However, its PSEP time is 455 million years suggesting probably damaging nature. It has thermolability (DG: -3.04 Kcal/mol). Its ligand propensity score is 2. In the L235F variant, there is disruption of all the NADP binding sites except for 201H and 437Y residues. This results in the formation of New H-bonds with K47, 51T, 54W, and K205 residues.
G6PD Union (R454C)
This is predicted to be deleterious by SIFT, Provean and SNAP2. Its PSEP time is 4200 million years suggesting probably damaging nature. Its ligand propensity score is 9. In the R454C variant, the NADP binding site is devoid of 199I, 200D, 201H, 246R, and 437Y residues. This leads to disruption of H-bond with 199I and the formation of new H-bonds with 40S, 42D, 72R, 140L, and 142L.