UNC45A deficiency causes microvillus inclusion disease-like phenotype by impairing myosin VB-dependent apical trafficking.

Variants in the UNC45A cochaperone have been recently associated with a syndrome combining diarrhea, cholestasis, deafness, and bone fragility. Yet the mechanism underlying intestinal failure in UNC45A deficiency remains unclear. Here, biallelic variants in UNC45A were identified by next-generation sequencing in 6 patients with congenital diarrhea. Corroborating in silico prediction, variants either abolished UNC45A expression or altered protein conformation. Myosin VB was identified by mass spectrometry as client of the UNC45A chaperone and was found misfolded in UNC45AKO Caco-2 cells. In keeping with impaired myosin VB function, UNC45AKO Caco-2 cells showed abnormal epithelial morphogenesis that was restored by full-length UNC45A, but not by mutant alleles. Patients and UNC45AKO 3D organoids displayed altered luminal development and microvillus inclusions, while 2D cultures revealed Rab11 and apical transporter mislocalization as well as sparse and disorganized microvilli. All those features resembled the subcellular abnormalities observed in duodenal biopsies from patients with microvillus inclusion disease. Finally, microvillus inclusions and shortened microvilli were evidenced in enterocytes from unc45a-deficient zebrafish. Taken together, our results provide evidence that UNC45A plays an essential role in epithelial morphogenesis through its cochaperone function of myosin VB and that UNC45A loss causes a variant of microvillus inclusion disease.

Novel PCNT variants in MOPDII with attenuated growth restriction and pachygyria.

Biallelic loss-of-function mutations in the centrosomal pericentrin gene (PCNT) cause microcephalic osteodysplastic primordial dwarfism type II (MOPDII), which is characterized by extreme growth retardation, microcephaly, skeletal dysplasia, and dental anomalies. Life expectancy is reduced due to a high risk of cerebral vascular anomalies. Here, we report two siblings with MOPDII and attenuated growth restriction, and pachygyria. Compound heterozygosity for two novel truncated PCNT variants was identified. Both truncated PCNT proteins were expressed in patient's fibroblasts, with a reduced total protein amount compared to control. Patient's fibroblasts showed impaired cell cycle progression. As a novel finding, 20% of patient's fibroblasts were shown to express PCNT comparable to control. This was associated with normal mitotic morphology and normal co-localization of mutated PCNT with centrosome-associated proteins γ-tubulin and centrin 3, suggesting some residual function of truncated PCNT proteins. These data expand the clinical and molecular spectrum of MOPDII and indicate that residual PCNT function might be associated with attenuated growth restriction in MOPDII.

Severe Deoxyguanosine Kinase Deficiency in Austria: A 6-Patient Series.

Mutations in the nuclear gene DGUOK, encoding deoxyguanosine kinase, cause an infantile hepatocerebral type of mitochondrial depletion syndrome (MDS). We report 6 MDS patients harboring bi-allelic DGUOK mutations, of which 3 are novel, including a large intragenic Austrian founder deletion. One patient was diagnosed with hepatocellular carcinoma aged 6 months, supporting a link between mitochondrial DNA depletion and tumorigenesis; liver transplantation proved beneficial with regard to both tumor treatment and psychomotor development.