DNAJB11-Related Atypical ADPKD in a Kidney Transplant Donor

DNAJB11 Mutation in ADPKD Patients: Clinical Characteristics in a Monocentric Cohort

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a late-onset cilia-related disorder, characterized by progressive cystic enlargement of the kidneys. It is genetically heterogeneous with PKD1 and PKD2 pathogenic variants identified in approximately 78% and 15% of families, respectively. More recently, additional ADPKD genes, such as DNAJB11, have been identified and included in the diagnostic routine test for renal cystic diseases. However, despite recent progress in ADPKD molecular approach, approximately ~7% of ADPKD-affected families remain genetically unresolved. We collected a cohort of 4 families from our center, harboring heterozygous variants in the DNAJB11 gene along with clinical and imaging findings consistent with previously reported features in DNAJB11 mutated patients. Mutations were identified as likely pathogenetic (LP) in three families and as variants of uncertain significance (VUS) in the remaining one. One patient underwent to kidney biopsy and showed a prevalence of interstitial fibrosis that could be observed in ~60% of the sample. The presence in the four families from our cohort of ADPKD characteristics together with ADTKD features, such as hyperuricemia, diabetes, and chronic interstitial fibrosis, supports the definition of DNAJB11 phenotype as an overlap disease between these two entities, as originally suggested by the literature.

Atypical ADPKD Due to a DNAJB11 Pathogenic Variant: An Educational Case Report

Rationale

Due to next-generation sequencing, variants in new genes such as DNAJB11 are recently being identified as causing atypical autosomal dominant polycystic kidney disease (ADPKD). It is important to describe phenotypes associated with these variants in order to increase awareness among clinicians, especially since genetic variability affects ADPKD severity.

Presenting Concerns of the Patient

We describe a 55-year-old female patient of Haitian origin who presented with slowly deteriorating kidney function, microscopic hematuria, proteinuria, enlarged kidneys with innumerable small cysts, and a family history of chronic kidney disease and cysts. The phenotype was atypical for ADPKD caused by PKD1 or PKD2 variants, since cysts were of small size, kidneys were only moderately enlarged, and the patient had no extra-renal involvement suggestive of typical ADPKD such as liver cysts, pancreatic cysts, cranial aneurysms, or cardiac abnormalities.

Diagnoses

A panel of genes was analyzed by next-generation massive sequencing techniques, including DNAJB11, DZIP1L, GANAB, HNF1B, PKD1, PKD2, and PKHD1. Genetic testing revealed a heterozygous variant in the DNAJB11 gene (c.123 dup), which is predicted to result in premature protein termination (p. Lys42*) and was classified by the laboratory as likely pathogenic.

Interventions

She was treated with candesartan 16 mg once daily to address her proteinuria.

Outcomes

At the time of the most recent follow-up, her proteinuria has increased, and her kidney function continues to slowly deteriorate.

Teaching Points

DNAJB11 variants are a rare cause of atypical ADPKD. It is important to recognize the clinical features that help distinguish DNAJB11 from PKD1 and PKD2 variants. Atypical ADPKD due to DNAJB11 variants is usually characterized by small cysts, normal kidney size, proteinuria, progressive chronic kidney disease, and phenotypic overlap with autosomal dominant tubulointerstitial kidney disease (ADTKD). It may, however, present itself with enlarged kidneys as was seen in our patient. Genetic testing should be offered whenever a patient presents atypical features of ADPKD, which also requires increased awareness among clinicians regarding the various phenotypes of atypical ADPKD.

Monoallelic IFT140 pathogenic variants are an important cause of the autosomal dominant polycystic kidney-spectrum phenotype

Autosomal dominant polycystic kidney disease (ADPKD), characterized by progressive cyst formation/expansion, results in enlarged kidneys and often end stage kidney disease. ADPKD is genetically heterogeneous; PKD1 and PKD2 are the common loci (∼78% and ∼15% of families) and GANAB, DNAJB11, and ALG9 are minor genes. PKD is a ciliary-associated disease, a ciliopathy, and many syndromic ciliopathies have a PKD phenotype. In a multi-cohort/-site collaboration, we screened ADPKD-diagnosed families that were naive to genetic testing (n = 834) or for whom no PKD1 and PKD2 pathogenic variants had been identified (n = 381) with a PKD targeted next-generation sequencing panel (tNGS; n = 1,186) or whole-exome sequencing (WES; n = 29). We identified monoallelic IFT140 loss-of-function (LoF) variants in 12 multiplex families and 26 singletons (1.9% of naive families). IFT140 is a core component of the intraflagellar transport-complex A, responsible for retrograde ciliary trafficking and ciliary entry of membrane proteins; bi-allelic IFT140 variants cause the syndromic ciliopathy, short-rib thoracic dysplasia (SRTD9). The distinctive monoallelic phenotype is mild PKD with large cysts, limited kidney insufficiency, and few liver cysts. Analyses of the cystic kidney disease probands of Genomics England 100K showed that 2.1% had IFT140 LoF variants. Analysis of the UK Biobank cystic kidney disease group showed probands with IFT140 LoF variants as the third most common group, after PKD1 and PKD2. The proximity of IFT140 to PKD1 (∼0.5 Mb) in 16p13.3 can cause diagnostic confusion, and PKD1 variants could modify the IFT140 phenotype. Importantly, our studies link a ciliary structural protein to the ADPKD spectrum.

Sequential genetic testing of living-related donors for inherited renal disease to promote informed choice and enhance safety of living donation

Living kidney donors (LKDs) with a family history of renal disease are at risk of kidney disease as compared to LKDs without such history suggesting that some LKDs may be pre-symptomatic for monogenic kidney disease. LKDs with related transplant candidates whose kidney disease was considered genetic in origin were selected for genetic testing. In each case, the transplant candidate was first tested to verify the genetic diagnosis. A genetic diagnosis was confirmed in 12 of 24 transplant candidates (ADPKD-PKD1: 6, ALPORT-COL4A3: 2, ALPORT-COL4A5: 1: nephronophthisis-SDCCAG8: 1; CAKUT-HNF1B and ADTKD-MUC1: 1 each) and 2 had variants of unknown significance (VUS) in phenotype-relevant genes. Focused genetic testing was then done in 20 of 34 LKDs. 12 LKDs screened negative for the familial variant and were permitted to donate; seven screened positive and were counseled against donation. One, the heterozygous carrier of a recessive disorder was also cleared. Six of seven LKDs with a family history of ADPKD were under 30 years and in 5, by excluding ADPKD, allowed donation to safely proceed. The inclusion of genetic testing clarified the diagnosis in recipient candidates, improving safety or informed decision-making in LKDs.