Unwrapping the Enigma: A Rare Case of MYH9 Nephropathy

Introduction: The MYH9 gene encodes the non-muscle myosin heavy chain IIA expressed in various tissues including podocytes and mesangial cells. Mutations in this gene lead to MYH9 related disorders (MYH9-RD) with an autosomal dominant pattern of inheritance characterized by macrothrombocytopenia with variable risk of non-hematologic features including nephropathy, cataracts and hearing loss. Lack of a family history does not rule out disease, as some mutations are sporadic. Case Description: A 56-year-old Caucasian female with a past medical history of thrombocytopenia in childhood was found to be hypertensive with an elevated creatinine (Cr) 3.23 mg/dl and a reduced eGFR 15 ml/min/1.73m2 during her wellness check which prompted a referral to nephrology. She had no skin rash, hematuria, dysuria, leg swelling or hemoptysis. She denied a history of kidney stones, recurrent urinary tract infections, hearing loss, cataracts or nonsteroidal anti-inflammatory (NSAID) use. Urinalysis showed proteinuria without hematuria, Urine Protein Creatinine ratio (UPCR) 4236 mg/g. Platelet count was 30,000 K/uL. Renal ultrasound revealed bilateral echogenic kidneys with no hydronephrosis, calculi or masses. Work up for proteinuria including antinuclear antibody (ANA), antineutrophil cytoplasmic antibodies (ANCA), anti-double stranded DNA, anti Glomerular basement membrane antibody, HIV, hepatitis panel, complements and immunofixation were negative. A renal biopsy was deferred due to thrombocytopenia. Hematology was consulted and a diagnosis of idiopathic thrombocytopenic purpura (ITP) was made. Genetic testing revealed a pathogenic mutation of c.4270G>A (p. Asp1424Asn) in exon 31 of MYH9 gene. Her blood pressure and antiproteinuric regimen was optimized with subsequent improvement in proteinuria. She was provided counseling by the genetic counselling team. Discussion: There is great heterogeneity among renal and nonrenal manifestations of MYH9 related disorders including age at presentation, quantity of proteinuria and rate of progression to ESRD. Disease prevalence is underestimated due to misdiagnosis. MYH9-RD should be considered in any patient presenting with renal failure and thrombocytopenia, as early diagnosis and therapy with RAAS blockade may slow progression to ESRD.