Bodo Beck / Janine Altmüller - C 1

Rare renal disorders identify core aspects of renal homeostasis - an integral approach to discover fundamental molecular principles of the kidney

The project represents an innovative approach to utilize Rare Kidney Disease (RKD) in order to gain knowledge about fundamental aspects of kidney and blood pressure homeostasis. This will yield new causative genes and advanced molecular understanding of genotypes that cause renal disease. Finally we  will provide missing links that change our perception of (molecular) renal physiology in health and disease.

Complete assembly of the VNTR in ADTKD-MUC1

The Mucin-1 (MUC1) gene has been identified as a causal gene of autosomal dominant tubulo-interstitial kidney disease (ADTKD). Most causative mutations are buried within a GC-rich 60 basepair variable number of tandem repeat (VNTR), which escapes identification by conventional or parallel sequencing due to the complexity of the VNTR.

We established long read single molecule real time sequencing (SMRT) targeted to the MUC1-VNTR as an alternative strategy to the snapshot assay. 

Our approach allows complete VNTR assembly, thereby enabling the detection of all variants residing within the VNTR as well as determination of VNTR length (Figure 1). By SMRT sequencing we confirmed the diagnosis in all previously tested cases, reconstruct both VNTR alleles and determine the exact position of the causative variant in eight of nine families. In summary we recommend to perform first line or complementary SMRT sequencing in all suspected ADTKD-MUC1 cases. 

Functional studies on MAGED2

We recently discovered mutations in the X-chromosomal MAGED2 gene as a novel cause for a transient form of antenatal Bartter-syndrome with severe polyhydramnios leading to prematurity and an increased risk for stillbirth. Besides several mutations affecting correct mRNA splicing, we identified a missense mutation (R446C) resulting in the expression of a full-length-protein. Subcellular fractionation as well as immunostaining experiments revealed altered protein MAGED2 localization within HEK293T and Cos-7 cells. We analysed interaction partners of MAGED2 via interactome and co-immunoprecipitation experiments and identified GNAS that binds wild-type but not R446C-MAGED2 protein. GNAS encodes the alpha-subunit of the stimulatory G protein (Gsα), which is a signaling protein able to increase NKCC2 and NCC expression and maturation via a cAMP-dependent pathway. As GNAS knock-out in mice had already been shown to result in impaired membrane expression of NKCC2, this could represent a pathomechanism of MAGED2 loss. 

Analysis of structural variations within the complement factor H gene cluster on chr 1q32 

Hemolytic uremic syndrome (HUS) is a rare but severe disease that belongs to a group of thrombotic microangiopathies (TMA) and arises from an initial endothelial cell injury. The atypical form (aHUS) is a consequence of the deregulation of the alternative pathway of the complement system and many mutations in the complement genes including structural variations have been detected already. Using the Molecular Combing Technology from Genomic Vision we designed probes to detect structural variations within the regulators of complement activation (RCA) cluster. We were able to receive a full haplotype view, that can close the gap of structural aberration detection in this region characterized by high sequence homology.

Biomarker discovery in kidney diseases

So far, no reliable biomarkers for screening, diagnostic, monitoring and therapy efficacy purposes have been successfully established in RKD. The investigation of cell free-DNA (cfDNA) in blood and urine is a promising approach for biomarker discovery, as cfDNA is obtainable from minimally or non-invasive procedures. Analyzing epi-genomic marks in cfDNA is a challenging task, for low abundance, little fragment size, and a short half-life. Nevertheless, precise measures of methylation profiles in promotor regions of genes exclusively transcribed in renal tissue and cell-type specific nucleosome footprints could qualify as biomarker.

Aims and Perspectives 

  • Identify novel genetic causes of RKD. Determine their frequency as well as their genotype and phenotype spectrum.  Integration of this data can provide missing links in the current concepts of renal physiology and may have therapeutic implications for common conditions beyond RKD.
  • Identify RKD biomarkers based on cfDNA. 

Selected publications

Laghmani K.*, Beck B.B.*, ..., Altmüller J., et al. (2016) Polyhydramnios, Transient Antenatal Bartter's Syndrome, and MAGED2 Mutations. N Engl J Med. May 12; 374(19):1853-63. *shared 1st authorship

Beck B.B., van Spronsen F., Diepstra A., et al. (2017). Renal thrombotic microangiopathy in patients with cblC defect: review of an under-recognized entity. Pediatr Nephrol May;32(5):733-741.

Wenzel A., Altmüller J., ..., Beck B.B.(2018). Single molecule real time sequencing in ADTKD-MUC1 allows complete assembly of the VNTR and exact positioning of causative mutations. Sci Rep. Mar 8;8(1):4170

van der Wijst J., ..., Altmüller J., Thiele H., Beck B., Schlingmann K.P., de Baaij J.H.F. (2018). A de novo KCNA1 Mutation in a Patient with tetany and Hypomagnesemia. Nephron. 139(4):359-366.

Braun D.A., ..., Altmüller J., ..., Khokha M., & Hildebrandt F. (2018).  Mutations in genes encoding four interacting components of the nuclear pore complex cause nephrotic syndrome. J Clin Invest (manuscript ID 98688-JCI-RG; in press).


Dr. Bodo Beck

Institute for Human Genetics / RG location - CMMC Building

Dr. Bodo Beck

Principal Investigator C 1

bodo.beck@uk-koeln.de

Work +49 221 478 86824

Institute for Human Genetics
Kerpener Str. 34
50931 Cologne

http://humangenetik.uk-koeln.de/

Publications - Bodo Beck

Link to PubMed


Dr. Janine Altmüller

Cologne Center for Genomics / RG location - CMMC Building

Dr. Janine Altmüller

Co-Principal Investigator C 1

janine.altmueller@uni-koeln.de

Work +49 221 478 96819

Cologne Center for Genomics (CCG), University of Cologne
Weyertal 115b
50931 Cologne

http://portal.ccg.uni-koeln.de/ccg/

Publications - Janine Altmüller

Link to PubMed

Group Members

Andrea Wenzel (PostDoc)
Florian Erger (Clinician Scientist)
Björn Reusch (PhD student)
Nikolai Tschernoster (PhD student)
Deborah Nörling (master student)

Figure 1

CMMC Research Beck Altmüller
MUC1-VNTR assembly of the risk allele in affected individuals of a Swiss family. The insC was detected in the second consensus repeat (highlighted in red). Nucleotide sequence differences within the 60mer repeat units are highlighted in dark grey. Uniform pseudo-repeats (nonvariable) units at beginning and at the end of the VNTR are underlined.

Figure 2

CMMC Research Beck Altmüller
NKCC2(Green) +TO5(Red) staining of placenta tissue (a) WT 23 + 3 weeks and (b) MAGED2 knockout 22 weeks.

Figure 3

CMMC Research Beck Altmüller
(a) ~360kb  WT segment containing the CFH_CFHR1-5 gene cluster with flanking control genes. (~650kb) (b) deletion of CFHR3 and CFHR1 (associated with FH autoantibodies)

Figure 4

CMMC Research Beck Altmüller
cfDNA is fragmented in a non-random manner, whereby nucleosome occupancy in the cell-of-origin can be reconstructed. Adapted from Snyder et al., Cell, 2016.