Autosomal-dominant hypophosphatemic rickets (ADHR) mutations stabilize FGF-23

Autosomal-dominant hypophosphatemic rickets (ADHR) mutations stabilize FGF-23.BackgroundThe gene for the renal phosphate wasting disorder autosomal-dominant hypophosphatemic rickets (ADHR) is FGF23, which encodes a secreted protein related to the fibroblast growth factors (FGFs). We previously detected missense mutations R176Q, R179W, and R179Q in FGF23 from ADHR kindreds. The mutations replace R residues within a subtilisin-like proprotein convertase (SPC) cleavage site 176RHTR-179 (RXXR motif). The goal of these studies was to determine if the ADHR mutations lead to protease resistance of FGF-23.MethodsThe ADHR mutations were introduced into human FGF-23 cDNA clones with or without an N-terminal FLAG tag by site-directed mutagenesis and were transiently transfected into HEK293 cells. Protein expression was determined by Western analyses.ResultsAntibodies directed toward the C-terminal portion of FGF-23 revealed that the native FGF-23 protein resolved as 32 kD and 12 kD species in HEK293 conditioned media; however, the three mutated proteins were detected only as the 32 kD band. An N-terminal FLAG-tagged native FGF-23 resolved as two bands of 36 kD and 26 kD when detected with a FLAG antibody, whereas the R176Q mutant resolved primarily as the 36 kD protein species. Cleavage of FGF-23 was not enhanced by extracellular incubation of FGF-23 with HEK293 cells. Native and mutant FGF-23s bound heparin.ConclusionsFGF-23 proteins containing the ADHR mutations are secreted, and produce polypeptides less sensitive to protease cleavage than wild-type FGF-23. Therefore, the ADHR mutations may protect FGF-23 from proteolysis, thereby potentially elevating circulating concentrations of FGF-23 and leading to phosphate wasting in ADHR patients

Hereditary Hypophosphatemic Rickets with Hypercalciuria Is Caused by Mutations in the Sodium-Phosphate Cotransporter Gene SLC34A3

Hypophosphatemia due to isolated renal phosphate wasting results from a heterogeneous group of disorders. Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is an autosomal recessive form that is characterized by reduced renal phosphate reabsorption, hypophosphatemia, and rickets. It can be distinguished from other forms of hypophosphatemia by increased serum levels of 1,25-dihydroxyvitamin D resulting in hypercalciuria. Using SNP array genotyping, we mapped the disease locus in two consanguineous families to the end of the long arm of chromosome 9. The candidate region contained a sodium-phosphate cotransporter gene, SLC34A3, which has been shown to be expressed in proximal tubulus cells. Sequencing of this gene revealed disease-associated mutations in five families, including two frameshift and one splice-site mutation. Loss of function of the SLC34A3 protein presumably results in a primary renal tubular defect and is compatible with the HHRH phenotype. We also show that the phosphaturic factor FGF23 (fibroblast growth factor 23), which is increased in X-linked hypophosphatemic rickets and carries activating mutations in autosomal dominant hypophosphatemic rickets, is at normal or low-normal serum levels in the patients with HHRH, further supporting a primary renal defect. Identification of the gene mutated in a further form of hypophosphatemia adds to the understanding of phosphate homeostasis and may help to elucidate the interaction of the proteins involved in this pathway

Mutations in EXOSC2 are associated with a novel syndrome characterised by retinitis pigmentosa, progressive hearing loss, premature ageing, short stature, mild intellectual disability and distinctive gestalt

Background Retinitis pigmentosa in combination with hearing loss can be a feature of different Mendelian disorders. We describe a novel syndrome caused by biallelic mutations in the 'exosome component 2' (EXOSC2) gene. Methods Clinical ascertainment of three similar affected patients followed by whole exome sequencing. Results Three individuals from two unrelated German families presented with a novel Mendelian disorder encompassing childhood myopia, early onset retinitis pigmentosa, progressive sensorineural hearing loss, hypothyroidism, short stature, brachydactyly, recognisable facial gestalt, premature ageing and mild intellectual disability. Whole exome sequencing revealed homozygous or compound heterozygous missense variants in the EXOSC2 gene in all three patients. EXOSC2 encodes the 'ribosomal RNA-processing protein 4' (RRP4)-one of the core components of the RNA exosome. The RNA exosome is a multiprotein complex that plays key roles in RNA processing and degradation. Intriguingly, the EXOSC2-associated phenotype shows only minimal overlap with the previously reported diseases associated with mutations in the RNA exosome core component genes EXOSC3 and EXOSC8. Conclusion We report a novel condition that is probably caused by altered RNA exosome function and expands the spectrum of clinical consequences of impaired RNA metabolism

Identification and Functional Testing of ERCC2 Mutations in a Multi-national Cohort of Patients with Familial Breast- and Ovarian Cancer

The increasing application of gene panels for familial cancer susceptibility disorders will probably lead to an increased proposal of susceptibility gene candidates. Using ERCC2 DNA repair gene as an example, we show that proof of a possible role in cancer susceptibility requires a detailed dissection and characterization of the underlying mutations for genes with diverse cellular functions (in this case mainly DNA repair and basic cellular transcription). In case of ERCC2, panel sequencing of 1345 index cases from 587 German, 405 Lithuanian and 353 Czech families with breast and ovarian cancer (BC/OC) predisposition revealed 25 mutations (3 frameshift, 2 splice-affecting, 20 missense), all absent or very rare in the ExAC database. While 16 mutations were unique, 9 mutations showed up repeatedly with population-specific appearance. Ten out of eleven mutations that were tested exemplarily in cell-based functional assays exert diminished excision repair efficiency and/or decreased transcriptional activation capability. In order to provide evidence for BC/OC predisposition, we performed familial segregation analyses and screened ethnically matching controls. However, unlike the recently published RECQL example, none of our recurrent ERCC2 mutations showed convincing co-segregation with BC/OC or significan

<i>ERCC2</i> allele frequencies (%) in BC/OC patients and corresponding control cohorts.

<p>The allele frequency is counted on the basis of sample size (in brackets) and number of observed cases (see <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1006248#pgen.1006248.t001" target="_blank">Table 1</a>) with hetero- and homozygosity.</p

<i>ERCC2</i> frameshift mutation c.1703_1704delTT (p.Phe568fs) in familial breast and ovarian cancer pedigrees.

<p>Individuals with breast cancer (BC), ovarian cancer (OC) or both (BC, OC) are shown as circles filled in black. Individuals tested positive for the familial mutation are indicated in detail; those with WT (wild-type) have been tested negative. All affected individuals with BC or OC not tested for germline mutations in ERCC2 were either deceased or refused testing. (A) German, (B) Lithuanian and (C-E) Czech pedigrees.</p

Nucleotide excision repair (NER) capacity and Transcriptional activity of breast cancer associated XPD/ERCC2 variants.

<p>(A) Several XPD/ERCC2 variants cloned into an expression vector were analyzed regarding to complementation of <i>ERCC2</i>-defective XP6BE cells overexpressing the NER-deficient R601W XPD mutant [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1006248#pgen.1006248.ref015" target="_blank">15</a>] (normalization for overexpression artifacts). Black bars indicate the mean relative repair capacity (in %, WT-XPD was set to 100%) of an UV irradiated firefly luciferase reporter gene plasmid (UVC 1000 J/m²) obtained by host cell reactivation (n>6 in triplicates). Red lines mark the range between DNA-repair levels of empty vector, i.e. residual repair activity of the cells, and WT-XPD, i.e. 100% repair capacity. (B) Dominant modulation of firefly luciferase reporter gene expression (without irradiation) via overexpression of XPD/ERCC2 BC/OC-associated variants was estimated in the transcriptionally-proficient but repair-deficient XPD/ERCC2-defective XP6BE cells. Black bars indicate the mean relative reporter gene expression (in %, empty vector control was set to 100%), obtained by CMV-promotor driven basal transcription (n>6 in triplicates). Error bars indicate the standard error of the mean. Significance levels were calculated, after pairwise testing for normal distribution of the values, using appropriate statistical tests for comparison of two groups (T-Test or U-Test, # = reference group, *** = p<0.001, ** = p<0.01, * = p<0.05, n.s. = not significant). (C) Additional characteristics of the mutations tested for repair efficiency and transcriptional activity.</p