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Kidney Week

Abstract: SA-PO758

TMEM67 Allelic and Other Effects Drive Vast Phenotypic Heterogeneity Across a Broad Spectrum of Ciliopathies

Session Information

Category: Genetic Diseases of the Kidneys

  • 1201 Genetic Diseases of the Kidneys: Cystic

Authors

  • Sieben, Cynthia J., Mayo Clinic Research Rochester, Rochester, Minnesota, United States
  • Czarnecki, Peter G., Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States
  • Heyer, Christina M., Mayo Clinic Research Rochester, Rochester, Minnesota, United States
  • Sturmlechner, Ines, Mayo Clinic Research Rochester, Rochester, Minnesota, United States
  • Harris, Peter C., Mayo Clinic Research Rochester, Rochester, Minnesota, United States
Background

Ciliopathies are genetically and phenotypically heterogeneous inherited diseases, impacting multiple organs systems, including kidneys. Kidney phenotypes include polycystic kidney disease (PKD) and renal cystic dysplasia, and genes associated with integrity/function of primary cilia. TMEM67 variants are found in several ciliopathies, with varying severity, including Meckel (MKS), Joubert syndromes (JBTS), and nephronophthisis (NPHP). MKS is the most severe, including perinatal lethality, PKD, CNS defects, CHF, and polydactyly. Whereas NPHP, tubulointerstitial nephritis and cysts, is the mildest. It is currently unclear how TMEM67 variants cause such an array of phenotypes and disease severity.

Methods

To investigate the pathogenicity, penetrance, and pathomechanisms of TMEM67 missense variants (19) across these diseases, we employed in vitro exogenous expression systems and patient derived cell lines to assess TMEM67 maturation/trafficking to the apical plasma membrane (glycosylation status/western blotting, surface immunolabelling/flow cytometry, and immunofluorescence [IF] imaging) and primary cilia transition zone [TZ; IF], and primary cilia protein composition (IF).

Results

All the MKS-associated TMEM67 missense variants that we assessed, are fully penetrant (7/7), and abolish trafficking of TMEM67 to the cell surface and TZ (1/1, patient cells). Whereas only a subset in the milder JBTS (7/13) and NPHP (2/5) diseases, are fully penetrant, and incompletely penetrant/mild and apparent neutral alleles are present (~31 and 60%, respectively). Interestingly, many of these variants (11/19) are misfolded and can be partially or completely rescued by enhancing folding conditions, even for the fully penetrant variants found in MKS (~57%). In addition, absence of TMEM67 from the TZ, perturbs trafficking of other ciliary proteins, inversin and ARL13B.

Conclusion

Our preliminary studies assessing 19 TMEM67 variants (MKS, JBTS, and NPHP) have revealed that: 1) allele penetrance correlates with disease severity to some degree (TMEM67 maturation/trafficking), 2) perturbed TMEM67 maturation/trafficking represents a common pathomechanism, resulting from defective TMEM67 folding in many cases; and 3) fully penetrant membrane trafficking variants also perturb primary cilia protein composition and TMEM67 TZ localization.

Funding

  • NIDDK Support