Autosomal dominant tubulointerstitial kidney disease with a novel heterozygous missense mutation in the uromodulin gene: A case report

BACKGROUND Autosomal dominant tubulointerstitial kidney disease(ADTKD)is a progressive chronic disease that is inherited in an autosomal dominant fashion.Symptoms include hyperuricemia,gout,interstitial nephritis,renal cysts,and progressive renal damage that can lead to end-stage renal disease.Mutations in the uromodulin gene(UMOD)characterize the ADTKD-UMOD clinical subtype of this disease.To date,>100 UMOD mutations have been identified.Early diagnosis of ADTKD-UMOD is important to treat the disease,slow down disease progression,and facilitate the identification of potentially affected family members.CASE SUMMARY We report a 40-year-old man harboring a novel heterozygous missense mutation in UMOD(c.554G>T;p.Arg185Leu).The patient had hyperuricemia,gout,and chronic kidney disease.The same mutation was detected in his daughter,aunt and cousin.CONCLUSION A single nucleotide substitution in exon 3 of UMOD was responsible for the heterozygous missense mutation(c.554G>T,p.Arg185Leu).

Genetic Testing of the mucin I gene-Variable Number Tandem Repeat Single Cytosine Insertion Mutation in a Chinese Family with Medullary Cystic Kidney Disease

Background： Medullary cystic kidney disease （MCKD） is clinically indistinguishable from several other autosomal-dominant renal diseases： thus, molecular genetic testing is needed to establish a definitive diagnosis. A specific type of single cytosine insertion in the variable number tandem repeat （VNTR） of the mucin 1 （MUC1） gene is the only known cause of MCKD1; however, genetic analysis of this mutation is difficult and not yet offered routinely. To identify the causative mutation/s and establish a definitive diagnosis in a Chinese family with chronic kidney disease, clinical assessments and genetic analysis were performed, including using a modified genotyping method to identify the MUC1-VNTR single cytosine insertion. Methods： Clinical data from three patients in a Chinese family with chronic kidney disease were collected and evaluated. Linkage analysis was used to map the causative locus. Mutation analysis of uromodulin （UMOD） gene was performed using polymerase chain reaction （PCR） and direct sequencing. For MUC1 genotyping, the mutant repeat units were enriched by Mwol restriction, and then were amplified and introduced into pMD-18T vectors. The 192 clones per transformant were picked up and tested by colony PCR and second round of Mwol digestion. Finally, Sanger sequencing was used to confirm the MUC1 mutation. Results： Clinical findings and laboratory results were consistent with a tubulointerstitial lesion. Linkage analysis indicated that the family was compatible with the MCKDI locus. No mutations were found in UMOD gene. Using the modified MUC1 genotyping method, we detected the MUC1-VNTR single cytosine insertion events in three patients of the family; and mutation-containing clones were 12/192, 14/192, and 5/96, respectively, in the three patients. Conclusions： Clinical and genetic findings could support the MCKDI diagnosis. The modified strategy has been demonstrated to be a practical way to detect MUCI mutation.