Pathogenic PHIP Variants are Variably Associated With CAKUT

Abstract

Introduction: Congenital anomalies of the kidney and urinary tract (CAKUT) represent the most common cause of chronic kidney disease in children. Although only 20% of cases can be genetically explained, the majority remain without an identified underlying etiology. The neurodevelopmental disorder Chung-Jansen syndrome (CHUJANS) is caused by haploinsufficiency of Pleckstrin homology domain-interacting protein (PHIP) and was previously associated with genital malformations. Anecdotal coincidence of CHUJANS and CAKUT prompted us to investigate whether urorenal malformations are part of the phenotypic spectrum of CHUJANS.

Methods: Analysis of existing CHUJANS and CAKUT cohorts, consulting matchmaking platforms, and systematic literature review to look for additional patients with both CHUJANS and CAKUT. Prenatal expression studies in murine and human renal tissues to investigate the role for PHIP in kidney development.

Results: We identified 4 novel and 8 published cases, indicating variable expressivity with a urorenogenital trait frequency of 5% to 35%. The prenatal expression studies supported a role for PHIP in normal kidney and urinary tract development.

Conclusion: Pathogenic PHIP gene variants should be considered as causative in patients with syndromal CAKUT. Conversely, patients with CHUJANS should be clinically evaluated for urorenogenital manifestations. Because neurodevelopmental disorders are often associated with kidney phenotypes, an interdisciplinary re-evaluation offers promise in identifying incompletely penetrant kidney associations and uncovering novel molecular mechanisms of disturbed nephrogenesis.

Keywords: CAKUT; Chung-Jansen syndrome (CHUJANS); PHIP.

Graphical abstract

Figure 1

Selected clinical images and pedigrees. (a–e) Illustrates index patient (ID1) aged 42 years: (a) Stature and facial appearance, (b) pedigree, indicating de novo status, (c) MRI of the kidneys with significant narrowing of the parenchyma and enlarged renal calyces, probably expression of chronic urinary stasis grade III-IV° (∗). Cortical kidney cyst left up to 2 cm in diameter (blue arrows), ultrasound imaging of the left (c) and the right (e) kidney. (f–k) illustrates ID 2.1: 99mTc-DMSA scintigraphy of the kidneys (f), ultrasound imaging of the left (g) and right (h) kidney with unilateral kidney hypoplasia, (i–j) syndactyly, (k) and pedigree of the family indicates autosomal inheritance.

Figure 2

(a) 2D structure of PHIP with pathogenic variants: red poles indicate nonsense (truncating), blue poles denote missense variants. (b) 3D modelling with main functional domains (alpha-fold model Q8WWQ0-F1) [32]: intact 3D structure of PHIP, (c) missense variant residues, (d–i) nonsense variant residues with truncated c-terminal region shown as transparent. (j–k) Frequency of genital anomalies and CAKUT in patients with CHUJANS.

Figure 3

Immunohistochemical staining targeting PHIP in human embryonic control kidneys. (a–b) 14 weeks of gestational age, (c–d) 22 weeks of gestational age. cM, Cortical mesenchyme; CapM, Cap mesenchyme; CT, Collecting tubule; DT, Distal tubule; G, Glomerulus; mM, Medullary mesenchyme; MV, Metanephric vesicle; PT, Proximal tubule; UBT, Uteric bud tip.

Figure 4

RNAScope in situ hybridization of Phip (pink) was conducted on mouse embryos at different developmental stages (a: TS20, b: TS22 and c: TS 24). Wt1 (green) was used as a marker for mesenchymal cells, comma/s-shaped bodies, and glomeruli in the developing kidney. Dapi (blue) was used for visualization of nuclei. (a–c) longitudinal section of the whole embryo. (d–f) Magnification of the developing mouse kidney from the dotted squares in (a–c). Scale bar in upper panels indicates 200 μm and in lower panels 1000 μm. Note: Unspecific green staining of erythrocytes in the heart and large blood vessels. AG, Adrenal gland; Dapi, 4’,6-diamidino-2-phenylindole; Dpc, Days post conceptionem; G, Glomerulus; Go, Gonad; Gu, Gut; H, Heart; K, Kidney; Li, Liver; Lu, Lung; MM, Metanephric mesenchyme; Phip, Pleckstrin homology domain-interacting protein; St, Stomach; TS, Teiler stage; UB, Uteric bud; Wt1, Wilms tumor 1.

Figure 5

RNAScope in situ hybridization and quantification of Phip expression of postnatal mouse kidneys at different developmental times (a–d) 3 days postnatal, (e–h) 7 days postnatal, (i–l) 14 days postnatal, (m–o) adult (11 weeks), (p) all stages-bar graph summary stastics. Wt1 (green) was used as a marker for glomeruli. Dapi (blue) was used for visualization of nuclei. Dotted squares represent the area from which images c, g, k, and n were acquired respectively. Scale bars represent 200 μm.