SMRT sequencing revealed to be an effective method for ADTKD-MUC1 diagnosis through follow-up analysis of a Chinese family

Abstract

We reported a large Chinese family diagnosed with autosomal dominant tubulointerstitial kidney disease caused by MUC1 mutation (ADTKD-MUC1). Cytosine duplication within a string of 7 cytosines in the variable-number tandem repeats (VNTR) region of the MUC1 gene was detected by long-read single-molecule real-time (SMRT) sequencing. MUC1 frameshift protein (MUC1fs) was found to be expressed in renal tubules and urinary exfoliated cells by pathological examination. The family, which consisted of 5 generations including 137 individuals, was followed for 5 years. Genetic testing was performed in thirty-four individuals, 17 of whom carried MUC1 mutations. The ADTKD-MUC1-affected individuals had an elevated incidence of hyperuricaemia without gout attack. Within five years, higher baseline levels of urinary α1-microglobulin were detected in affected individuals with rapidly progressing renal failure than in affected individuals with stable renal function, and the increases manifested even before increases in serum creatinine. This study demonstrates that SMRT sequencing is an effective method for the identification of MUC1 mutations. The pathological examination of MUC1fs expression in renal tissue and urinary exfoliated cells can contribute to early screening of family members suspected to be affected. It is suggested that affected individuals with elevated urinary α1microglobulin levels should be closely monitored for renal function. Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a hereditary disease characterized by progressive tubulointerstitial nephropathy that ultimately leads to end-stage renal disease (ESRD) 1-4. To date, four genes mutation which causes ADTKD have been identified: uromodulin (UMOD) 5 , mucin-1 (MUC1) 6 , renin (REN) 7 and hepatocyte nuclear factor 1β (HNF1B) 8. The disease forms caused by these mutations were named ADTKD-UMOD, ADTKD-MUC1, ADTKD-REN and ADTKD-HNF1B, respectively. Recently, a SEC. 61A1 mutation was identified as a novel cause of ADTKD 9. The manifestations of ADTKD are nonspecific, including autosomal dominant inheritance, bland urinary sediment with absent or mild proteinuria, progressive kidney failure, and, in some cases, multiple small renal cysts 1-3,10,11. Renal histology shows interstitial fibrosis and tubular atrophy, varying degree of nephrosclerosis and arteriolar thickening. Immunofluorescence or immunostaining on the renal tissue is negative. Electron microscopy usually showed irregular width and lamelation of the glomerular basement membrane and particular the tubular basement membrane 2,12-14. The diagnosis of ADTKD-MUC1 depends on genetic analysis. The MUC1 gene, located on chromosome 1q21, contains 20-125 copies of a repetitive sequence of 60 basepair in the variable-number tandem repeats (VNTR) domain 13. Most MUC1 mutations are caused by duplication of a cytosine within a seven-cytosine stretch in the VNTR region that produces a frameshift muatation, resulting in MUC1 frameshift protein (MUC1fs) 6,14-16. In addition, mutations in other areas of ...

Detecting MUC1 Variants in Patients Clinicopathologically Diagnosed With Having Autosomal Dominant Tubulointerstitial Kidney Disease

“…Wang et al. 8 also revealed the usefulness of SMRT sequencing for detecting MUC1 VNTR mutations in a large Chinese family. Nevertheless, owing to their study design, these 2 studies did not determine the detection rate of MUC1 VNTR variants in patients with clinically suspected ADTKD.…”

“…7 Wang et al also demonstrated the usefulness of SMRT sequencing for detecting MUC1 VNTR mutations in a large Chinese family. 8 However, owing to their study design, these two studies did not determine the detection rate of MUC1 VNTR variants in patients with clinically suspected ADTKD. In this study, we clarified that the diagnostic rate of MUC1 variants in patients with clinically suspected ADTKD was 18.8%, which may facilitate more accurate probabilities, especially during genetic counseling.…”

“…Recent studies have found the usefulness of LRSs, which use a single-molecule real-time (SMRT) sequencing method to identify MUC1 VNTR variants. 7 , 8 Nevertheless, MUC1 VNTR variants have not yet been characterized in the Japanese population. In addition, the prevalence of MUC1 variants in patients with clinically suspected ADTKD remains unknown.…”

Autosomal dominant tubulointerstitial kidney disease genotype and phenotype correlation in a Chinese cohort

“…Studies from Europe and America showed a varied prevalence of ADTKD-MUC1. ADTKD-MUC1 was reported to be rare in Chinese 23,24 . The clinical manifestations of hereditary cystic kidney disease were hard to distinguish, therefore, suspected ADTKD patient without ADTKD gene mutations may be due to other hereditary kidney diseases.…”

“…Sequence reads were aligned to the reference sequence NM_001204286 and analyzed using NextGENE software. The MUC1 mutation positive control was donated by professor Hong Cheng 24 .…”