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Malignancy-induced hypercalcemia is a very rare condition in children whereas it is more common among adult patients with malignancy. The mechanisms of malignancy-induced hypercalcemia include the over-secretion of parathyroid hormone-related protein (PTHrP), osteolytic metastases and the over-production of 1,25-dihydroxyvitamin D (calcitriol). Although hypercalcemia due to PTHrP secretion has been published before, overproduction of calcitriol has not been reported yet in pediatric squamous cell skin carcinoma cases. Herein, we report calcitriol-mediated severe hypercalcemia in a 5-year-old boy with squamous cell skin carcinoma arising in the background of xeroderma pigmentosum (XP) which responded well to zoledronate treatment. To the best of our knowledge, this is the first pediatric case of malignancy-induced hypercalcemia which is mediated by calcitriol in squamous cell skin carcinoma., NA

Friedreich's ataxia (FRDA) is a rare neurodegenerative disorder which is caused by triplet repeat expansion (GAA) in the first intron of FXN gene. In this present study, we generated induced pluripotent stem cells (iPSC) lines from fibroblasts of three unrelated FRDA patients using integration-free episomal vectors. All iPSC lines express the pluripotency markers such as OCT4 and SSEA4, display normal karyotypes and can differentiate into all three germ layers via in vivo teratoma formation assay., NA

The redox state of the neural progenitors regulates physiological processes such as neuronal differentiation and dendritic and axonal growth. The relevance of endoplasmic reticulum (ER)-associated oxidoreductases in these processes is largely unexplored. We describe a severe neurological disorder caused by bi-allelic loss-of-function variants in thioredoxin (TRX)-related transmembrane-2 (TMX2); these variants were detected by exome sequencing in 14 affected individuals from ten unrelated families presenting with congenital microcephaly, cortical polymicrogyria, and other migration disorders. TMX2 encodes one of the five TMX proteins of the protein disulfide isomerase family, hitherto not linked to human developmental brain disease. Our mechanistic studies on protein function show that TMX2 localizes to the ER mitochondria-associated membranes (MAMs), is involved in posttranslational modification and protein folding, and undergoes physical interaction with the MAM-associated and ER folding chaperone calnexin and ER calcium pump SERCA2. These interactions are functionally relevant because TMX2-deficient fibroblasts show decreased mitochondrial respiratory reserve capacity and compensatory increased glycolytic activity. Intriguingly, under basal conditions TMX2 occurs in both reduced and oxidized monomeric form, while it forms a stable dimer under treatment with hydrogen peroxide, recently recognized as a signaling molecule in neural morphogenesis and axonal pathfinding. Exogenous expression of the pathogenic TMX2 variants or of variants with an in vitro mutagenized TRX domain induces a constitutive TMX2 polymerization, mimicking an increased oxidative state. Altogether these data uncover TMX2 as a sensor in the MAM-regulated redox signaling pathway and identify it as a key adaptive regulator of neuronal proliferation, migration, and organization in the developing brain.

Hypohidrotic or anhidrotic ectodermal dysplasia (HED/EDA) is characterized by impaired development of the hair, teeth, or sweat glands. HED/EDA is inherited in an X-linked, autosomal dominant, or autosomal recessive pattern and caused by the pathogenic variants in 4 genes: EDA, EDAR, EDARADD, and WNT10A. The aim of the present study was to perform molecular screening of these 4 genes in a cohort of Turkish individuals diagnosed with HED/EDA. We screened for pathogenic variants of WNT10A, EDA, EDAR, and EDARADD through Sanger sequencing. We further assessed the clinical profiles of the affected individuals in order to establish phenotype-genotype correlation. In 17 (63%) out of 27 families, 17 pathogenic variants, 8 being novel, were detected in the 4 well-known ectodermal dysplasia genes. EDAR and EDA variants were identified in 6 families each, WNT10A variants in 4, and an EDARADD variant in 1, accounting for 35.3, 35.3, 23.5, and 5.9% of mutation-positive families, respectively. The low mutation detection rate of the cohort and the number of the EDAR pathogenic variants being as high as the EDA ones were the most noteworthy findings which could be attributed to the high consanguinity rate., Scientific and Technological Research Council of Turkey (TÜBİTAK); Programme Hospitalier de Recherches Cliniques (PHRC); CRANIRARE of the European Research Area Network projects (E-RARE); CRANIRARE-2 of the European Research Area Network projects (E-RARE); European Union (European Union); Horizon 2020

The four R-spondin secreted ligands (RSPO1–RSPO4) act via their cognate LGR4, LGR5 and LGR6 receptors to amplify WNT signalling1–3. Here we report an allelic series of recessive RSPO2 mutations in humans that cause tetra-amelia syndrome, which is characterized by lung aplasia and a total absence of the four limbs. Functional studies revealed impaired binding to the LGR4/5/6 receptors and the RNF43 and ZNRF3 transmembrane ligases, and reduced WNT potentiation, which correlated with allele severity. Unexpectedly, however, the triple and ubiquitous knockout of Lgr4, Lgr5 and Lgr6 in mice did not recapitulate the known Rspo2 or Rspo3 loss-of-function phenotypes. Moreover, endogenous depletion or addition of exogenous RSPO2 or RSPO3 in triple-knockout Lgr4/5/6 cells could still affect WNT responsiveness. Instead, we found that the concurrent deletion of rnf43 and znrf3 in Xenopus embryos was sufficient to trigger the outgrowth of supernumerary limbs. Our results establish that RSPO2, without the LGR4/5/6 receptors, serves as a direct antagonistic ligand to RNF43 and ZNRF3, which together constitute a master switch that governs limb specification. These findings have direct implications for regenerative medicine and WNT-associated cancers. Independently of the LGR4/5/6 receptors, RSPO2 acts as a direct antagonistic ligand to RNF43 and ZNRF3 during embryogenesis, and specifies the position and number of limbs that an embryo should form.

In this Letter, the surname of author Lena Vlaminck was misspelled 'Vlaeminck'. In addition, author Kris Vleminckx should have been associated with affiliation 16 (Center for Medical Genetics, Ghent University, Ghent, Belgium). These have been corrected online.