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MYH9 related diseases are caused by mutations in the MYH9 gene and constitute a rare group of genetic entities. Its inheritance follows an autosomal dominant pattern. The MYH9 gene, encodes the nonmuscle myosin heavy chain IIA, expressed in different tissues and especially in podocytes and mesangial cells. The disorder is characterized by the presence of macrothrombocytopenia, leukocyte inclusions and a variable risk of developing renal failure, hearing loss and early-onset cataracts. We describe the case of a 27-year-old Caucasian woman, diagnosed initially with idiopathic thrombocytopenic purpura. After a detailed family history and the appearance of renal involvement and hearing loss, genetic testing allowed to make the diagnosis of nephropathy associated with MYH9 mutation. This case is an example of the delayed diagnosis of uncommon diseases and highlights the usefulness genetic testing. A review of the disease is provided. Resumen: Las enfermedades relacionadas con mutaciones del gen MYH9 son un grupo de patologías genéticas raras. Su herencia sigue un patrón autosómico dominante en donde el gen MYH9, codifica la cadena pesada de la miosina IIA no muscular que se expresa en diferentes tejidos pero especialmente en los podocitos y en las células mesangiales. Este trastorno se caracteriza por la presencia de macrotrombocitopenia, inclusiones leucocitarias y un riesgo variable de desarrollar insuficiencia renal, hipoacusia y cataratas en edad juvenil o adulta. Describimos el caso de una mujer de 27 años, de raza caucásica, diagnosticada inicialmente de púrpura trombocitopénica idiopática. Tras una detallada historia familiar y el desarrollo de síntomas clínicos posteriores con afectación renal e hipoacusia, se le realizó un estudio genético que nos permitió el diagnóstico de nefropatía asociada a la mutación en el gen MYH9. Este caso destaca el retraso del diagnóstico y la utilidad del estudio genético en pacientes con enfermedades muy poco frecuentes. Se procede a la revisión de la enfermedad en este artículo. Keywords: MYH9 nephropathy, Hearing loss, Thrombocytopenia, Alport syndrome, Epstein syndrome, May-Hegglin anomaly, Palabras clave: Nefropatía MYH9, Hipoacusia, Trombocitopenia, Síndrome de Alport, Síndrome de Epstein, Anomalía de May-Hegglin, Sindrome de Sebastián

Rationale & Objective Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a rare underdiagnosed cause of end-stage renal disease (ESRD). ADTKD is caused by mutations in at least 4 different genes: MUC1, UMOD, HNF1B, and REN. Study Design Retrospective cohort study. Setting & Participants 56 families (131 affected individuals) with ADTKD referred from different Spanish hospitals. Clinical, laboratory, radiologic, and pathologic data were collected, and genetic testing for UMOD, MUC1, REN, and HNF1B was performed. Predictors Hyperuricemia, ultrasound findings, renal histology, genetic mutations. Outcomes Age at ESRD, rate of decline in estimated glomerular filtration rate. Results ADTKD was diagnosed in 25 families (45%), 9 carried UMOD pathogenic variants (41 affected members), and 16 carried the MUC1 pathogenic mutation c.(428)dupC (90 affected members). No pathogenic variants were identified in REN or HNF1B. Among the 77 individuals who developed ESRD, median age at onset of ESRD was 51 years for those with ADTKD-MUC1 versus 56 years (P=0.1) for those with ADTKD-UMOD. Individuals with the MUC1 duplication presented higher risk for developing ESRD (HR, 2.24; P=0.03). The slope of decline in estimated glomerular filtration rate showed no significant difference between groups (−3.0mL/min/1.73m2 per year in the ADTKD-UMOD group versus −3.9mL/min/1.73m2 per year in the ADTKD-MUC1 group; P=0.2). The prevalence of hyperuricemia was significantly higher in individuals with ADTKD-UMOD (87% vs 54%; P=0.006). Although gout occurred more frequently in this group, the difference was not statistically significant (24% vs 7%; P=0.07). Limitations Relatively small Spanish cohort. MUC1 analysis limited to cytosine duplication. Conclusions The main genetic cause of ADTKD in our Spanish cohort is the MUC1 pathogenic mutation c.(428)dupC. Renal survival may be worse in individuals with the MUC1 mutation than in those with UMOD mutations. Clinical presentation does not permit distinguishing between these variants. However, hyperuricemia and gout are more frequent in individuals with ADTKD-UMOD.

Molecular diagnosis of inherited kidney diseases remains a challenge due to their expanding phenotypic spectra as well as the constantly growing list of disease-causing genes. Here we develop a comprehensive approach for genetic diagnosis of inherited cystic and glomerular nephropathies. Targeted next generation sequencing of 140 genes causative of or associated with cystic or glomerular nephropathies was performed in 421 patients, a validation cohort of 116 patients with previously known mutations, and a diagnostic cohort of 207 patients with suspected inherited cystic disease and 98 patients with glomerular disease. In the validation cohort, a sensitivity of 99% was achieved. In the diagnostic cohort, causative mutations were found in 78% of patients with cystic disease and 62% of patients with glomerular disease, mostly familial cases, including copy number variants. Results depict the distribution of different cystic and glomerular inherited diseases showing the most likely diagnosis according to perinatal, pediatric and adult disease onset. Of all the genetically diagnosed patients, 15% were referred with an unspecified clinical diagnosis and in 2% genetic testing changed the clinical diagnosis. Therefore, in 17% of cases our genetic analysis was crucial to establish the correct diagnosis. Complex inheritance patterns in autosomal dominant polycystic kidney disease and Alport syndrome were suspected in seven and six patients, respectively. Thus, our kidney-disease gene panel is a comprehensive, noninvasive, and cost-effective tool for genetic diagnosis of cystic and glomerular inherited kidney diseases. This allows etiologic diagnosis in three-quarters of patients and is especially valuable in patients with unspecific or atypical phenotypes.

Rationale & Objective: Alport syndrome is a common genetic kidney disease accounting for approximately 2% of patients receiving kidney replacement therapy (KRT). It is caused by pathogenic variants in the gene COL4A3, COL4A4, or COL4A5. The aim of this study was to evaluate the clinical and genetic spectrum of patients with autosomal dominant Alport syndrome (ADAS). Study Design: Retrospective cohort study. Setting & Participants: 82 families (252 patients) with ADAS were studied. Clinical, genetic, laboratory, and pathology data were collected. Observations: A pathogenic DNA variant in COL4A3 was identified in 107 patients (35 families), whereas 133 harbored a pathogenic variant in COL4A4 (43 families). Digenic/complex inheritance was observed in 12 patients. Overall, the median kidney survival was 67 (95% CI, 58-73) years, without significant differences across sex (P = 0.8), causative genes (P = 0.6), or type of variant (P = 0.9). Microhematuria was the most common kidney manifestation (92.1%), and extrarenal features were rare. Findings on kidney biopsies ranged from normal to focal segmental glomerulosclerosis. The slope of estimated glomerular filtration rate change was -1.46 (-1.66 to -1.26) mL/min/1.73 m(2) per year for the overall group, with no significant differences between ADAS genes (P = 0.2). Limitations: The relatively small size of this series from a single country, potentially limiting generalizability. Conclusions: Patients with ADAS have a wide spectrum of clinical presentations, ranging from asymptomatic to kidney failure, a pattern not clearly related to the causative gene or type of variant. The diversity of ADAS phenotypes contributes to its underdiagnosis in clinical practice.