Testing for the cytosine insertion in the VNTR of the MUC1 gene in a cohort of Italian patients with autosomal dominant tubulointerstitial kidney disease.

INTRODUCTION: Medullary cystic kidney disease type 1 (MCKD1; OMIM #174000) is a familial progressive tubule-interstitial nephropathy belonging to the recently defined group of autosomal dominant tubulointerstitial kidney diseases (ADTKD). CASE REPORT: A specific type of cytosine insertion in the extracellular variable number tandem repeat (VNTR) domain of the MUC1 gene causing the disease was tested in a group of 21 families with ADTKD. We identified this type of MUC1 mutation in two families, whose affected members are described in detail in this case report. Affected (ADTKD-MUC1) members developed end-stage renal disease (ESRD) with a higher incidence (p = 0.033) and at a younger age (p = 0.013) than probands with ADTKD but without this type of mutation. All patients with MUC1-associated kidney disease shared a rather unspecific tubule-interstitial laboratory pattern without medullary cysts, leading to ESRD between the age of 33 and 47 years. We were not able to identify any single common extra-renal feature among affected patients, even if they had various comorbidities, which are described in detail. CONCLUSIONS: We identified this type of MUC1 mutation in 9.5 % of families from an ADTKD Italian cohort; larger studies are needed to better define the criteria for genetic testing for this type of mutation.

Variations in the high-mobility group-A2 gene (HMGA2) are associated with idiopathic short stature.

BACKGROUND: Several association studies confirmed high-mobility group-A2 gene (HMGA2) polymorphisms as the most relevant variants contributing to height variability. Animal models and deletions in humans suggest that alterations of HMGA2 might be relevant in causing short stature. Together, these observations led us to investigate the involvement of HMGA2 in idiopathic short stature (ISS) through an association study and a mutation screening. METHODS: We conducted an association study (155 ISS patients and 318 normal stature controls) with three HMGA2 single-nucleotide polymorphisms (SNPs) (SNPs rs1042725, rs7968682, and rs7968902) using a TaqMan-based assay. The patients were then analyzed by direct sequencing and multiplex ligation-dependent probe amplification (MLPA) to detect point mutations and genomic micro-rearrangements. RESULTS: Considering a recessive model, an OR value >1 was observed for genotypes rs7968682 TT (Odds ratio (OR) = 1.72, confidence interval (CI): 1.14-2.58) and rs1042725 TT (OR = 1.51, CI: 1.00-2.28) in accordance to the effect exhibited by the single alleles in the general population. None of the patients carried possibly causative HMGA2 mutations. CONCLUSION: Besides the already known role in determining variability in human height, HMGA2 polymorphisms also contribute to susceptibility to ISS. Moreover, we here report the first mutation screening performed in ISS concluding that HMGA2 has not a significant impact on the monogenic form of ISS.

Frequency of genetic defects in combined pituitary hormone deficiency: a systematic review and analysis of a multicentre Italian cohort.

OBJECTIVE: Combined pituitary hormonal deficiency (CPHD) can result from mutations within genes that encode transcription factors. This study evaluated the frequency of mutations in these genes in a cohort of 144 unrelated Italian patients with CPHD and estimated the overall prevalence of mutations across different populations using a systematic literature review. MATERIAL AND METHODS: A multicentre study of adult and paediatric patients with CPHD was performed. The PROP1, POU1F1, HESX1, LHX3 and LHX4 genes were analysed for the presence of mutations using direct sequencing. We systematically searched PubMed with no date restrictions for studies that reported genetic screening of CPHD cohorts. We only considered genetic screenings with at least 10 individuals. Data extraction was conducted in accordance with the guidelines set by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). RESULTS: Global mutation frequency in Italian patients with CPHD was 2·9% (4/136) in sporadic cases and 12·5% (1/8) in familial cases. The worldwide mutation frequency for the five genes calculated from 21 studies was 12·4%, which ranged from 11·2% in sporadic to 63% in familial cases. PROP1 was the most frequently mutated gene in sporadic (6·7%) and familial cases (48·5%). CONCLUSION: The frequency of defects in genes encoding pituitary transcription factors is quite low in Italian patients with CPHD and other western European countries, especially in sporadic patients. The decision of which genes should be tested and in which order should be guided by hormonal and imaging phenotype, the presence of extrapituitary abnormalities and the frequency of mutation for each gene in the patient-referring population.

Novel mutations in the GH gene (GH1) uncover putative splicing regulatory elements.

Mutations affecting exon 3 splicing are the main cause of autosomal dominant Isolated GH Deficiency II (IGHDII) by increasing the level of exon 3-skipped mRNA encoding the functionally inactive dominant-negative 17.5-kDa isoform. The exons and introns of the gene encoding GH (GH1) were screened for the presence of mutations in 103 sporadic isolated GH deficiency cases. Four different variations within exon 3 were identified in 3 patients. One carried c.261C>T (p.Pro87Pro) and c.272A>T (p.Glu91Val), the second c.255G>A (p.Pro85Pro) and c.261 C>T, and the third c.246G>C (p.Glu82Asp). All the variants were likely generated by gene conversion from an homologous gene in the GH1 cluster. In silico analysis predicted that positions c.255 and c.272 were included within 2 putative novel exon splicing enhancers (ESEs). Their effect on splicing was confirmed in vitro. Constructs bearing these 2 variants induced consistently higher levels both of transcript and protein corresponding to the 17.5-kDa isoform. When c.255 and c.272 were combined in cis with the c.261 variant, as in our patients, their effect was weaker. In conclusion, we identified 2 variations, c.255G>A and c.272A>T, located in 2 novel putative exon splicing enhancers and affecting GH1 splicing in vitro by increasing the production of alternatively spliced isoforms. The amount of aberrant isoforms is further regulated by the presence in cis of the c.261 variant. Thus, our results evidenced novel putative splicing regulatory elements within exon 3, confirming the crucial role of this exon in mRNA processing.

Chronic renal failure of unknown origin is caused by HNF1B mutations in 9% of adult patients: a single centre cohort analysis.

BACKGROUND: HNF1B gene mutations might be an underdiagnosed cause of nephropathy in adult patients mainly because of their pleomorphic clinical presentations. As most studies are based on paediatric populations, it is difficult to assess the likelihood of finding HNF1B mutations in adult patients and consequently define clinical settings in which genetic analysis is indicated. The aim of this study was the search for mutations in the HNF1B gene in a cohort of unrelated adult patients with nephropathy of unknown aetiology. METHODS: Patients were tested for the HNF1B gene if they had chronic kidney disease of unknown origin and renal structure abnormalities (RSA) or a positive family history of nephropathy. The HNF1B coding sequence and intron-exon boundaries were analysed by direct sequencing. The search for gene deletions was performed by Multiple Ligation Probe Analysis (MLPA). RESULTS: Heterozygous mutations were identified in 6 out of 67 screened patients (9.0%) and included two whole gene deletions, one nonsense (p.Gln136Stop), two missense (p.Gly76Cys and p.Ala314Thr) mutations and a frameshift microdeletion (c.384_390 delCATGCAG), the latter two (c.384_390 del and p.Ala314Thr) not ever being reported to date. Mean age of the mutated patients at screening was 48.5 years with a M/F ratio of 2/4. The clinical manifestations of affected patients were extremely pleomorphic, including several urological and extra-renal manifestations. CONCLUSIONS: Mutations of HNF1B could explain chronic kidney disease in up to 9% of adult patients with a nephropathy of unknown aetiology and RSA: therefore an HNF1B mutation analysis should be considered in this group of patients.