⁃ Individuals must meet all the following inclusion criteria to be eligible to participate in this study:

• Prior kidney biopsy demonstrating FSGS obtained within 10 years prior to the screening visit.

• Age \>=18 years weighing more than 50 kg.

• If the patient is on immunosuppressive therapy (e.g., prednisone, cyclosporine, tacrolimus or mycophenolate mofetil) he/she should be on these medications for at least 3 months prior to study evaluation and should be on a stable dose of the medication for at least 4 weeks before start of trial, with no plans to alter the regimen during 12 weeks of study period, except to stabilize levels and/or for any safety concerns.

• Subjects will be allowed to continue with standard of care (SOC) non-immunosuppressant antiproteinuric agents to include RAAS inhibitors, mineralocorticoid antagonists (MRA), sodium-glucose co-transporter-2 inhibitors (SGLT2i), non-dihydropyridine calcium channel blockers (NDHP-CCBs), and glucagon-like peptide-1 (GLP-1) receptor agonists, in addition to other SOC adjuvant therapies such as diuretics, if they are able to maintain a stable dose throughout the trial. Subjects and their primary nephrologists will be encouraged to optimize their SOC treatments as much as possible prior to trial commencement. Subjects must be on a stable dose for at least 4 weeks before start of trial. Subjects should attempt to keep stable doses of both immunosuppressants and anti-proteinuric drugs throughout trial duration, to avoid confounding effects. Patients not receiving any of these SOC agents either due to allergy or intolerance will still be eligible.

• Subjects must have a spot random urine PCR of \>= 2g/g on each of 3 measurements collected on at least 2 separate days during screening period plus a 24-hr urine protein collection of \>= 2g/day. The rationale for using this degree of proteinuria is that proteinuria beyond this threshold value significantly increases the risk of progressive decline of renal functions in the absence of effective therapies to mitigate this risk. Conversely, this threshold value could also allow for the selection of a cohort of patients who are most likely to benefit from ManNAc therapy.

• Subjects with an estimated glomerular filtration rate (eGFR) \>=45 mL/min/1.73/m\^2 using the race-free CKD-EPI 2021 equation based on creatinine and cystatin-C \[Inker et al, 2021\]. The rationale is that below this eGFR threshold, sialic acid, the key metabolite of ManNAc markedly accumulates and may potentially result in systemic toxicity. Prior pharmacokinetic studies have shown that renal elimination of sialic acid is primarily through glomerular filtration, and it is neither reabsorbed nor secreted in the renal tubules. Hence decline in eGFR below 45 mL/min/1.73m\^2 directly correlates with rising blood sialic acid levels \[Fuentes et al, 2020\], in addition, these subjects may not benefit as much from ManNAc therapy as they have advanced disease pathology, which may be irreversible. Future studies with personalized precision ManNAc dosing may benefit the patient population with eGFR \<45 mL/min/1.73m\^2.

• Subjects of reproductive potential must be willing to use at least one effective form of birth control throughout the trial period, unless they have had a permanent birth control procedure/intervention including but not limited to hysterectomy, tubal ligation and/or vasectomy. These may include the following: barrier methods (such as condoms), oral or depot injection (for example, Norplant or Depo-Provera) contraception medication, and/or intrauterine devices.

• Evidence of a personally signed and dated informed consent indicating that the patient has been informed of all pertinent aspects of the study and their willingness to comply with all aspects of the study and their willingness to comply with all aspects of the study protocol, including treatment plan, laboratory tests, baseline and follow-up visits and procedures that include completion of daily diaries to record symptoms and medication intake.