#2850 EFFICIENCY OF THE GENETIC STUDY IN THE DIAGNOSIS OF AUTOSOMAL DOMINANT TUBULOINTERSTITIAL NEPHROPATHY
Authors: Gómez Cristina Andrades , Cosano Gema Montilla , Oporto Francisco Roca , Prieto Francisco Javier Toro , Lopez-Mendoza Manuel 
Published: June 2023

Abstract

Background and Aims
Autosomal dominant tubulointerstitial nephropathy (ADTKD) is a rare underdiagnosed cause of chronic kidney disease (CKD). ADTKD is a renal disease with a non-specific phenotypic expression that cause a slow progression over time. Given the great variability in its inter-familial presentation and among the same family members carrying the same mutation, its diagnosis is a challenge. Five genes have been identified to date such as Uromodulin (UMOD), Renin (REN), Hepatocyte Nuclear Factor 1b (HNF1β), Mucin-1 (MUC1) and, more recently, new genes, SEC61A1(encoding protein transport protein Sec61 subunit α and atypical (DNAJB11). Our main objective is to analyze the diagnostic yield of the genetic study in cases of clinical suspicion of ADTKD in patients with CKD of unknown etiology. We present a case series of patients from our center with CKD of unknown etiology and clinical suspicion of ADTKD. Genetic analysis of the gene SEC61A1 and DNAJB11 was not available at that time.

Method
This is a descriptive observational retrospective study from 2016 to 2021 at the Virgen del Rocio University Hospital in Seville, Spain. A total of 26 cases had phenotypic presentation of ADTKD. We collected clinical, laboratory, radiologic, and pathologic data. We performed in all the cases genetic testing for UMOD, MUC1, REN and HNF1β mutations. We collected data in a database, including age of presentation of kidney disease, sex, family history of kidney disease, the presence of hypertension at early age (defined as under 40 years of age), hyperuricemia (defined as uric acid &gt;7.5 mg/dl) at early age (&lt;40 years), hemoglobin at the time of diagnosis, age at last follow up with renal function and estimated glomerular filtration rate (eGFR) using the CKD-EPI (CKD Epidemiology Collaboration), urine elemental, renal ultrasound and renal biopsy if it had been performed. Descriptive results of quantitative variables are expressed as median. For categorical data, frequency and percentage are reported.

Results
Of the 26 cases with suspected ADTKD, 4 cases presented a genetic study that confirmed the diagnosis, that is, 15% of the cases. The median age at the time of the diagnosis was 41 years (IQR 32.7–48). 84% of the cases were male; 34% of cases had a family history of CKD of unknown etiology. 65% percent of the cases had a history of hyperuricemia at early age (&lt;40 years), with a personal history of hypertension &lt;40 years in 30% of the cases; 44% of the cases had renal lithiasis. The median glomerular filtration rate (CKD-EPI) at the time of diagnosis was 70 ml/min/1.73 m2 (46.4–70.7). In most of the patients, the urine elemental was normal. Renal cysts were found on ultrasound in 46% of patients. In 5 of the twenty-six patients a renal biopsy was performed, in which 60% presented data compatible with ADTKD with interstitial fibrosis and tubular atrophy. 4 of the patients with clinical suspicion of ADTKD obtained a genetic study that confirmed the diagnosis. The most frequently identified gene was HNF1β, being present in two of the four patients. The other genes identified were UMOD and MUC. The results are summarized in Table 1.

Conclusion
Adequate selection of patients based on clinical suspicion is essential to give greater profitability to the genetic study of this entity. The negativity of the study cannot exclude the diagnosis, since at the moment not all the causative genes of this pathology have been identified and it is necessary to use massive sequencing techniques or even the analysis of the complete exome to see the possibility of other variants of the disease.