Early recurrence of focal segmental glomerulosclerosis in a kidney transplant recipient with APOL1 one risk variant

Abstract

Apolipoprotein 1 (APOL1) risk variants (G1 and G2) are associated with focal segmental glomerulosclerosis (FSGS) in patients of African ancestry. The prevalence of APOL1 two risk variants is lower in Hispanics and very rare in European and Asian populations. APOL1 two risk variants in donor kidneys is associated with recipient kidney graft loss, however the effect of recipient risk variant in the kidney transplant outcome is unclear. Here, we present a late adolescent male with FSGS and end stage renal disease with one APOL1 risk variant (G2) who had immediate recurrence of FSGS in the post-KT period. There was an excellent response to few sessions of plasmapheresis and Rituximab with no further recurrence of FSGS in the 1 year follow-up period. It needs to be seen whether the recipient APOL1 single risk variant causes increased susceptibility to kidney graft loss on a long run via recurrent or de novo pathologies.

Background

The Apolipoprotein 1 (APOL1) gene belongs to the APOL gene family on human chromosome 22.¹ Two APOL1 risk variants (G1 and G2) are present disproportionately in people of recent African ancestry as compared with other ethnicities.² The c.1024AG (p.Ser342Gly) and c.1152TG (p.Ile384Met) variants represent the first risk allele (G1), and the c.1164_1169del (p. Asn388_Tyr389del) variant is the second risk allele (G2). Although known to provide protection against African trypanosomiasis, these APOL1 variants have been shown to be associated with focal segmental glomerulosclerosis (FSGS), HIV-associated nephropathy (HIVAN) and hypertensive nephropathy.¹ There is a substantial increased risk of renal disease with two risk alleles as compared with the one risk allele.¹ Hence, APOL1 risk alleles seem to follow the recessive mode of inheritance although APOL1 is not associated with Mendelian inheritance as opposed to other podocyte gene mutations. Kidney transplant (KT) recipients from a donor with two APOL1 risk alleles demonstrate an increased risk of kidney allograft failure.³ Whether recipient APOL1 status is also linked to the allograft failure or FSGS recurrence is not very clear, as there have been conflicting reports of such in a few published studies.^{4 5} Here we report an 18-year-old man with one APOL1 risk variant (G2) who received a kidney from a Caucasian donor and developed recurrent FSGS in the immediate post-KT period.

Case presentation

A late adolescent male presented with generalised oedema, decreased urine output, hypoalbuminemia and nephrotic range proteinuria. There were no other extra-renal symptoms. He had no history of usage of non-steroidal anti-inflammatory drugs and other medications known to cause nephrotic syndrome (NS). There was no other significant medical history, including hypertension and diabetes. He was born at full term in the USA with birth weight of seven pounds. There was no family history of kidney disease, NS or consanguinity. His parents were of Hispanic ethnicities. He was treated with multiple sessions of hypertonic albumin and diuretics for symptomatic relief of oedema. Investigations for secondary causes of NS including but not limited to HIV, hepatitis B and C, syphilis, SARS-CoV-2 and parvovirus B19 PCR were all negative. Given the age of onset of presentation, he underwent a renal biopsy. Light microscopy showed 24 glomeruli, seven of which were globally sclerotic. Eight glomeruli showed segmental sclerosis, hyalinosis, podocyte hyperplasia and foam cells. There was no collapse of glomerular capillary tuft seen. The capillary walls had no spikes. There were no crescents, fibrinoid necrosis or endocapillary hypercellularity. Interstitial fibrosis and tubular atrophy were seen in 40% of the cortical sample. Arteries and arterioles were unremarkable. Electron microscopy showed partial podocyte foot process effacement (figure 1A and B). FSGS was classified as ‘not otherwise specified’ type. The FSGS was not responsive to steroid and calcineurin inhibitors. He subsequently progressed to end stage renal disease (ESRD). The ESRD was managed with three times weekly haemodialysis (HD) along with three times a week 25% albumin during the HD sessions for severe hypoalbuminemia, persistent nephrotic range proteinuria and clinical oedema. He had native kidneys in situ and was not oliguric. Medical nephrectomy with ACE inhibitor was attempted without success. After 1 year after being on HD, he received a deceased donor KT from an adult Caucasian donor whose APOL1 genotyping status was not known. The pretransplant panel reactive antibody titre was 0% for both class I and class II human leucocyte antigen antibodies (Luminex bead assay). The virtual crossmatch of the recipient with the deceased donor was negative before the transplant. Pretransplant plasmapheresis was not done to prevent the prolonged cold ischaemia time (CIT). Prior to the transplant, the plasmapheresis was not considered due to difficulty in determining the timing of availability of the deceased donor kidney. The living donor option was not available. At the time of the KT, he underwent bilateral native nephrectomies. Donor was negative for HIV, hepatitis B and C and had no history of hypertension, diabetes or known kidney disease. The terminal serum creatinine was 0.9 mg/dL. The CIT was 12 hours and warm ischaemia time was 35 min. The induction immunosuppression (IS) was done with three doses of Thymoglobulin 1.5 mg/kg and iv 500 mg methylprednisolone. The maintenance IS consisted of tacrolimus, mycophenolate mofetil and prednisone. The post-transplant period was significant for immediate recurrence of the NS in the allograft which was manifested by nephrotic range proteinuria, hypoalbuminemia, oedema and weight gain.

Figure 1.

(A) A glomerulus showing sclerosis in more than half of glomerulus capillary tuft, associated with podocyte hyperplasia (H&E stain 40×10). (B) Podocyte foot processes effacement detected by Electron microscopy (Direct Mag: 8000).

Investigations

Renal function post-KT showed stable serum creatinine of 0.8–1 mg/dL with serum albumin ranging from 2.1 to 2.5 g/dL. Random urine protein to creatinine ratio (UPCR) varied from 3 to 5 mg/mg. A renal transplant biopsy was not obtained. SARS-CoV-2 PCR and parvovirus B19 PCR were both negative. Fasting serum lipid levels were elevated. Serum trough tacrolimus levels were in the goal range of 10–12 ng/mL in the first month of KT. Cytomegalovirus (CMV), Epstein-Barr virus and BK virus DNA PCRs were negative in the first 6 months of KT.

Differential diagnosis

The most important differential diagnoses included recurrent FSGS post-KT given known history of FSGS. Other possibilities were occurrence of de novo FSGS in the recipient from a donor with APOL1 high risk alleles, viral infections such as HIV, parvovirus B19 and SARS-CoV-2, obesity-related FSGS and medications such as heavy metals, non-steroidal anti-inflammatory drugs, pamidronate and tumour necrosis factor alpha inhibitors. Donor was a Caucasian, hence the possibility of carrying two APOL1 risk alleles was minimal. However, the donor’s genotype was not done and hence this merely remains an assumption. The recipient’s HIV status was negative, all viral PCRs were negative and there was no history of intake of drugs causing secondary FSGS. His body mass index was 26.1 kg/m².

Treatment

The recurrent FSGS was treated with six sessions of every other day plasmapheresis (1.3 plasma volume exchange with 5% albumin as replacement fluid) followed by weekly intravenous Rituximab 375 mg/m²/dose for four dosages. His serum albumin normalised, and proteinuria decreased with random UPCR of 0.2–0.4 mg/mg. He then received Rituximab 375 mg/m²/dose every 3 months. Post-KT course was also complicated by CMV and BK viremia around 6 months after transplant which responded to lowering of IS with a goal trough tacrolimus level of 3–5 ng/mL, valganciclovir and switching of mycophenolate to leflunomide.

Pretransplant genetic study was not obtained. Post-transplant genetic study showed that the patient was heterozygous in the APOL1 gene for a sequence variant c.1164_1169del, which is predicted to result in an in-frame deletion (p. Asn388_Tyr389del). There were no variants seen in the nephrin, podocin and MYH9, among others.

Outcome and follow-up

Follow-up 1 year after KT showed a stable serum creatinine of 1.2 mg/dL with normal serum albumin. Random UPCR was 0.2 mg/mg. There was no oedema with excellent urine output. All viral PCRs at 1 year post-KT were negative.

Discussion

APOL1 risk variants (G1 and G2) have been associated with increased risk of non-diabetic chronic kidney disease and progression to ESRD. As mentioned above, one risk allele has only minimal to no effect on kidney disease.¹ African- American is the third most common ethnicity in the USA (White alone, non-Hispanic or non-Latino: 59.3%; Hispanic or Latino: 18.9%; African-American: 13.6%; US census data, 2022). Many people of recent African ancestry possess at least one APOL1 risk allele (about 50%) and 12% possess two risk alleles.⁶ These risk variants are even more common in the subset of this population with FSGS.² In Hispanics, the prevalence of two APOL1 risk alleles is 20% and 6% in patients with non-diabetic and diabetic ESRD, respectively.⁷ The frequency of occurrence of these risk variants is less than 1% in European and Asian populations.⁸ Having two APOL1 risk alleles is associated with a 29-fold increased risk for HIVAN, 17-fold increased risk for FSGS and 7.3-fold increased risk for hypertension-attributed ESRD.^{2 6 9} Hence, APOL1-risk variants contribute significantly to the renal morbidity. Therapeutic options for APOL1-mediated FSGS are limited. However, one recent study showed a promising efficacy of inaxaplin in reducing proteinuria in patients with two APOL1 risk alleles and FSGS.¹⁰

In normal kidneys, APOL1 localises in the podocyte, proximal tubular epithelial cell and in medium-sized arterial and arteriolar endothelial cells.¹¹ The number of APOL1-positive podocytes and tubular cells is diminished in FSGS and it has been shown that there is a de novo appearance of APOL1 within the cells of the arterial medial wall.¹¹ It is postulated that APOL1 causes arterial wall damage and vascular dysfunction.¹¹ We did not have data on the APOL1 staining of the renal biopsy as the biopsy was not obtained. APOL1-associated FSGS is thought to be secondary to dose-dependent podocyte injury from the dominant toxic gain of function of the high risk APOL1 variants.¹² Although APOL1-associated FSGS has been described mostly with two risk alleles, even a single risk allele is associated with cellular/tissue changes with some studies showing increased risk of chronic kidney disease with single G1 or G2 alleles.^{2 13–15}

FSGS is an important cause of ESRD in children.¹⁶ Idiopathic FSGS recurs in about one-third of cases of KT and is associated with a significant risk of graft loss, thought to be due to the presence of circulating factors which then causes podocyte injury in the allograft.¹⁷ Renal histology is not required to diagnose recurrent FSGS and if obtained, may be negative in the early post KT period. With regard to the inherited forms of FSGS, more than 75 genes known to cause steroid resistant NS, including FSGS, have been identified.¹⁶ Most inherited forms of FSGS typically do not recur after KT except in some patients with NPHS1 pathogenic variants leading to a complete absence of nephrin.^{18 19} The recurrence in these patients is believed to be due to an immune-mediated process leading to antibody production against the donor nephrin protein.²⁰ The optimal therapy for treatment of recurrent FSGS post-KT is not well defined in children and adolescents. Some of the common therapeutic approaches include plasmapheresis, high dose calcineurin inhibitor, with or without Rituximab.^{16 21–23} The role of prophylactic plasmapheresis in prevention of recurrent FSGS post-KT is not well established.²⁴

There is a conflicting data on the risk of post-transplant FSGS recurrence in recipients with APOL1 high-risk variants. It is known that a donor with two risk alleles is an important risk factor for development of FSGS in the allograft of the recipient.³ Additional second hits such as viral infections can cause de novo collapsing glomerulopathy in the recipients who receive kidneys from these donors with high-risk alleles.^{25 26} However, a recipient with two risk alleles may not have increased risk of recurrent FSGS, given intrinsic pathogenic role of APOL1 variants in the kidney tissue.⁴ Lee et al studied 119 KT recipients of African ancestry, about half of them had two APOL1 risk variants, and concluded that those with high-risk APOL1 genotypes have similar allograft survival at 5 years as compared with the ones with zero or only one risk allele.⁴ These observations are consistent with the idea that kidney APOL1, rather than circulating APOL1 produced primarily by the liver is the critical factor in driving APOL1 kidney disease.²⁷ In contrast, another study showed that recipient APOL1 risk alleles are associated with T-cell mediated rejection and allograft loss.²⁸ In their study, Zhang et al showed that the recipient APOL1 genotypes impact transplant outcomes and the immune response.²⁸ Independent of ancestry and within the subgroup of African American and Hispanic recipients, the number of recipient APOL1 G1/G2 alleles associated with an increased risk of death-censored allograft loss. The T-cell mediated rejection events were also higher with recipient APOL1 G1/G2 alleles. The authors showed the immunomodulatory role of recipient APOL1 risk alleles by detecting enriched immune response gene pathways in risk allele carriers compared with non-carriers on the KT waitlist and among healthy controls.²⁸

The role of pretransplant native nephrectomy in prevention of recurrent FSGS post-KT is not very clear.²⁴ Some transplant centres routinely perform native nephrectomies prior to or at the time of transplantation in patients with FSGS who still have significant diuresis, nephrotic range proteinuria and hypoalbuminemia before KT. This approach assists the nephrologists in monitoring for FSGS recurrence post-KT. However, some studies have shown that bilateral native nephrectomy as performed in our patient, rather increases the risk of FSGS recurrence post-KT.²⁹ Although the exact aetiology of the recurrent FSGS in these patients is not known, it is postulated that the native kidneys absorb the pathogenic circulating factors leading to reduction of the free circulating factors, and if removed, these factors may damage the podocytes in the transplanted kidney.³⁰

Our patient mentioned in this report is of Hispanic ethnicity. APOL1 genetic risk variants are predominantly found in people of recent African ancestry which confer CKD and proteinuria risk. However, these variants have also been demonstrated in people of Hispanic ethnicity although at a much lower rate.³¹ Hence, the single risk APOL1 variant seen in this patient could merely be a chance event. However, it is important to mention that these risk variants in Hispanic population can also be associated with an increased CKD and proteinuria risk.³¹ Also, Santoriello et al reported that the donor APOL1 high-risk genotypes, but not recipient, are associated with increased risk of de novo collapsing FSGS.³² Hence, a definite cause-and-effect relationship between recipient APOL1 single risk allele and recurrent FSGS cannot be established from this report. However, it does raise an important question of whether this needs to be studied in further larger studies. In the USA, an observational study called ‘APOL1 Long-term Kidney Transplantation Outcomes Network’ (APOLLO) is prospectively assessing kidney allograft survival from donors with recent African ancestry based on donor and recipient APOL1 genotypes and hopefully will fill this unmet need.³³

One of the limitations of our study include unavailability of donor APOL1 genotyping. However, given the ethnicity of the donor, the probability of having donor high risk APOL1 alleles is low. Whether there is a need to implement donor APOL1 genotyping at a widespread level, mainly the donors with recent African ancestry, will remain to be studied at a larger scale. This would possibly prevent allocating the high-risk kidneys to children who are expected to have longer estimated post-transplant life expectancy. Other limitations include the absence of pretransplant genetic testing, renal transplant biopsy and hence measurement of glomerular APOL1 gene expression, short-term follow-up of only 1 year and absence of determination of the presence of circulating factor. Since FSGS is known to recur even long after transplantation, a longer follow-up is also important. Also, the efficacy of maintenance Rituximab treatment needs to be determined in this subset of patients.

Patient’s perspective.

I was extremely excited and at the same time worried when I received the kidney transplant. I was concerned that my focal segmental glomerulosclerosis (FSGS) might recur after the transplant. When I had recurrence of the FSGS after transplant, I thought that I may go back on the dialysis. I was also worried when I received the genetics result showing that I carry one high risk allele of the APOL1 gene. However, with the treatments such as plasmapheresis and Rituximab, and the careful monitoring by my doctors, I am feeling great. I hope that I keep my kidney transplant healthy for a long time.

Learning points.

• Apolipoprotein 1 (APOL1) high risk alleles are associated with HIV-associated nephropathy, focal segmental glomerulosclerosis (FSGS) and hypertension-related kidney disease.

• Donor APOL1 high risk alleles are associated with poor kidney allograft outcome in the recipient.

• Whether recipient APOL1 high risk alleles lead to poor kidney allograft outcome is not clear, but may be associated with early recurrence of FSGS after kidney transplantation.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s).