Steroid-Resistant Focal Segmental Glomerulosclerosis with Alport-like Glomerular Basement Membrane Lesions Due to a MYO1E Mutation: A Pediatric Case Report

Steroid-resistant nephrotic syndrome (SRNS) in childhood frequently reflects monogenic podocytopathies in which immunosuppression is ineffective. Biallelic variants in <i>MYO1E</i>, encoding the class I myosin Myo1E, cause a distinctive form of focal segmental glomerulosclerosis (FSGS) often accompanied by "Alport-like" multilamination of the glomerular basement membrane (GBM). Early recognition has therapeutic and prognostic implications. A previously healthy 4-year-old boy presented with generalized edema and nephrotic-range proteinuria. Glucocorticoids induced no remission; sequential calcineurin inhibition (cyclosporine, then tacrolimus) and a single dose of ofatumumab yielded only transient, partial reductions in proteinuria. A first biopsy elsewhere showed FSGS with nonspecific IgM/C3 trapping; electron microscopy (EM) was not performed. At age 10, repeat biopsy with EM revealed ~30% segmental foot-process effacement, focal GBM thickening (to 1740 nm), irregular lamina densa multilamination, and lamellar duplications without immune-complex deposits-features highly suggestive of hereditary GBM disease. Targeted sequencing identified compound-heterozygous <i>MYO1E</i> variants segregating in trans: a canonical splice-donor change (c.2785+1G>A) and a frameshift (c.3094_3097del; p.Thr1032Profs*73). Each parent was an unaffected heterozygous carrier; the sibling was negative. Supportive therapy with ramipril was continued. At last follow-up (January 2025), renal function was normal (serum creatinine 0.5 mg/dL; creatinine clearance 122 mL/min) with stable sub-nephrotic proteinuria (0.52 g/day; 16 mg/m² per hour) and normotension. This case broadens clinicopathologic recognition of <i>MYO1E</i>-associated nephropathy and highlights the teaching point that Alport-like GBM changes are not pathognomonic for type IV collagen disorders but may signal defects in podocyte cytoskeletal anchoring.