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.

Functional SNPs within the intron 1 of the PROP1 gene contribute to combined growth hormone deficiency (CPHD).

CONTEXT: Mutations within the PROP1 gene represent one of the main causes of familial combined pituitary hormone deficiency (CPHD). However, most of the cases are sporadic with an unknown genetic cause. OBJECTIVE: The aim of this study was the search for low penetrance variations within and around a conserved regulatory element in the intron 1 of PROP1, contributing to a multifactorial form of the disease in sporadic patients. METHODS AND PATIENTS: A fragment of 570 bp encompassing the conserved region was sequenced in 107 CPHD patients and 294 controls, and an association study was performed with the four identified variants, namely c.109+435G>A (rs73346254), c.109+463C>T (rs4498267), c.109+768C>G (rs4431364), and c.109+915_917ins/delTAG (rs148607624). The functional role of the associated polymorphisms was evaluated by luciferase reporter gene expression analyses and EMSA. RESULTS: A statistically significant increased frequency was observed in the patients for rs73346254A (P = 5 × 10(-4)) and rs148607624delTAG (P = 0.01) alleles. Among all the possible allele combinations, only the haplotype bearing both risk alleles showed a significantly higher frequency in the patients vs. controls (P = 4.7 × 10(-4)) and conferred a carrier risk of 4.19 (P = 1.2 × 10(-4)). This haplotype determined a significant decrease of the luciferase activity in comparison with a basal promoter and the other allelic combinations in GH4C and MCF7 cells (P = 4.6 × 10(-6); P = 5.5 × 10(-4), respectively). The EMSA showed a differential affinity for nuclear proteins for the alternative alleles of the two associated variations. CONCLUSIONS: Variations with a functional significance conferring susceptibility to CPHD have been identified in the PROP1 gene, indicating a multifactorial origin of this disorder in sporadic cases.

Association of HLA class I markers with multiple sclerosis in the Italian and UK population: evidence of two independent protective effects.

BACKGROUND: The association of HLA A*02 with multiple sclerosis (MS) was recently confirmed by the authors, and it was observed that the combined presence of HLA Cw*05 significantly enhanced (threefold) the protective effect of HLA A*02. OBJECTIVES AND METHODS: Since A*02-Cw*05 is carried by two HLA extended haplotypes characterised by the B*4402 and B*1801 alleles, respectively, the association analysis was extended to HLA B*44 and B*18 in an Italian sample (1445 MS cases and 973 controls) and these associations were verified in a UK cohort (721 MS cases, 408 controls and 480 family trios). RESULTS: A strong protective effect, independent of DR15, of the A*02-Cw*05 combination carrying B*44 (OR 0.27, p=3.3×10(-5)) was seen in the Italian samples and confirmed in UK family trios (OR 0.33, p=5.5×10(-4)) and in a combined cohort of UK families and case-controls (OR 0.53, p=0.044). This protective effect was significantly stronger than that mediated by A*02 alone. Logistic regression showed that A*02-Cw*05 maintained a significant protection when adjusted for B alleles (Italy: OR 0.38, p=6.5×10(-7); UK: OR 0.60, p=0.0029), indicating that it was not secondary to linkage disequilibrium with B*44. Different from A*02, the other HLA class I tested markers individually showed no significant (Cw*05, B*18) or a modest (B*44) protection when adjusted for the remaining markers. CONCLUSIONS: This study identified at least two independent protective effects which are tagged by A*02-Cw*05 and A*02, respectively. Further studies are needed to elucidate whether this protective effect is due to the presence of an unanalysed factor characterising the HLA extended haplotype(s) carrying A*02 and Cw*05 or to a direct interaction between these alleles.

A recurrent signal peptide mutation in the growth hormone releasing hormone receptor with defective translocation to the cell surface and isolated growth hormone deficiency.

CONTEXT: Mutations in the GHRH receptor (GHRHR) have been detected in the familial type-IB isolated GH deficiency (IGHD-IB) inherited as an autosomal recessive disorder and characterized by a low but detectable serum GH level and good response to substitutive GH therapy. OBJECTIVE: The aim of our study was the identification of mutations in sporadic patients with a IGHD-IB phenotype. SUBJECTS AND METHODS: The GHRHR gene was systematically screened by DHPLC in 134 IGHD patients with no family history of the disorder or declared parental consanguinity. RESULTS: We identified a novel variation, Val10Gly, within the signal peptide at the heterozygous state in three patients and in one of 1084 controls (P = 0.004), suggesting that it might contribute to IGHD. The functional analysis showed that the signal peptide is not cleaved from the mutant GHRHR, which in turn is not translocated to the cellular surface, demonstrating that 10Gly drastically affects the receptor correct processing. Because 10Gly was also present in normal-stature relatives of the patients as well as in a control, it is likely that it exerts its effects in the context of other genetic and environmental susceptibility factors. CONCLUSION: At difference from previous papers reporting GHRHR mutations in familial cases with a clear recessive mode of inheritance, our study was conducted on a large sample of sporadic patients and allowed to discover a novel mechanism of the disease caused by a recurrent dominant mutation in the GHRHR signal peptide associated with incomplete penetrance.

A functional common polymorphism in the vitamin D-responsive element of the GH1 promoter contributes to isolated growth hormone deficiency.

CONTEXT: Causal mutations have been detected only in a minority of isolated GH deficiency (IGHD) patients. Idiopathic IGHD might be the result of the interaction between several low-penetrance genetic factors and the environment. OBJECTIVE: The aim of this study was to test the contribution to IGHD of genetic variations in the GH1 gene regulatory regions. DESIGN AND PATIENTS: A case-control association study was performed including 118 sporadic IGHD patients with a nonsevere phenotype (height -4/-1 sd score and partial GH deficiency) and two control groups, normal stature (n=200) and short-stature individuals with normal GH secretion (n=113). Seven single-nucleotide polymorphisms in the GH1 promoter, one in the IVS4 region, and two in the locus control region were analyzed. RESULTS: The -57T allele within the vitamin D-responsive element showed a positive significant association when comparing patients with normal (P=0.006) or short stature (P=0.0011) controls. The genotype -57TT showed an odds ratio of 2.93 (1.44-5.99) and 2.99 (1.42-6.31), respectively. The functional relevance of the -57 variation was demonstrated by the luciferase assay in the presence of vitamin D. The vitamin D-induced inhibition of luciferase activity was significantly (P=0.012) stronger for the promoter haplotype carrying the associated variation -57T [haplotype #1 (hp#1)] with respect to hp#2, bearing -57G. Replacement of the T with a G at -57 on hp#1 abolished the repression, demonstrating that the T at position -57 is necessary to determine the greater vitamin D-induced inhibitory effect of hp#1. EMSA experiments showed a different band-shift pattern of the T and G sequences. CONCLUSION: The common -57G-->T polymorphism contributes to IGHD susceptibility, indicating that it may have a multifactorial etiology.

Neuropeptide s receptor 1 gene polymorphism is associated with susceptibility to inflammatory bowel disease.

BACKGROUND & AIMS: The neuropeptide S receptor (NPSR1) gene has been associated recently with asthma and maps in a region of chromosome 7 previously linked also to inflammatory bowel disease (IBD). NPSR1 is expressed on the epithelia of several organs including the intestine, and appears to be up-regulated in inflammation. We tested NPSR1 gene polymorphism for association with IBD and verified whether the expression of its 2 major isoforms (NPSR1-A and NPSR1-B) is altered in the intestine of IBD patients. METHODS: Eight NPSR1 polymorphisms were genotyped in 2490 subjects from 3 cohorts of IBD patients and controls from Italy, Sweden, and Finland. Real-time polymerase chain reaction and immunohistochemistry were used to quantify NPSR1 messenger RNA (mRNA) and protein expression in intestinal biopsy specimens from IBD patients and controls. RESULTS: Global analysis of the whole dataset identified strong association of a NPSR1 haplotype block with IBD (P = .0018) and its 2 major forms: Crohn's disease (CD) (P = .026) and ulcerative colitis (UC) (P = .003). Genetic effects caused by individual haplotypes were identified mainly for the predisposing haplotype H2 in CD (P = .0005) and the protective haplotype H8 in UC (P = .003). NPSR1 mRNA and protein levels were increased in IBD patients compared with controls, and the risk haplotype H2 correlated with higher expression of both NPSR1-A (P = .024) and NPSR1-B (P = .047) mRNAs. CONCLUSIONS: NPSR1 polymorphism is associated with IBD susceptibility. Specific NPSR1 alleles might act as genetic risk factors for chronic inflammatory diseases of the epithelial barrier organs.

Variations in the coding and regulatory sequences of the angiogenin (ANG) gene are not associated to ALS (amyotrophic lateral sclerosis) in the Italian population.

Potentially causative missense variations in the ANG gene and a positive association with the synonymous rs11701-G substitution was detected mainly in Irish and Scottish ALS patients. We screened 262 Italian SOD1 negative ALS patients (250 sporadic) and 415 matched controls for sequence variations in the coding, 3'/5' UTR and 5' flanking (642 bp) regions of the ANG gene. We identified 53 sequence variations of which 46 new, 20 with a minor allele frequency (MAF) >or=0.01 and only three localised in the coding sequence, namely the missense I46V, identified in one patient and two controls, and the synonymous G86G and T97T corresponding to rs11701 and rs2228653. None of the detected SNPs or of their haplotypic combinations was significantly associated with ALS susceptibility or clinical features. In conclusion, we did not detect the association with rs11701-G or with any other newly detected variation in the ANG regulatory region. Furthermore we did not identify potentially causal mutations in the coding region.

Linkage disequilibrium screening for multiple sclerosis implicates JAG1 and POU2AF1 as susceptibility genes in Europeans.

By combining all the data available from the Genetic Analysis of Multiple sclerosis in EuropeanS (GAMES) project, we have been able to identify 17 microsatellite markers showing consistent evidence for apparent association. As might be expected five of these markers map within the Major Histocompatibility Complex (MHC) and are in LD with HLA-DRB1. Individual genotyping of the 12 non-MHC markers confirmed association for three of them--D11S1986, D19S552 and D20S894. Association mapping across the candidate genes implicated by these markers in 937 UK trio families revealed modestly associated haplotypes in JAG1 (p=0.019) on chromosome 20p12.2 and POU2AF1 (p=0.003) on chromosome 11q23.1.

A variation in a Pit-1 site in the growth hormone gene (GH1) promoter induces a differential transcriptional activity.

The proximal promoter of the human growth hormone gene (GH1) is highly polymorphic. We tested if promoter haplotypes differing at possibly functional sites, namely -278T/G (in the NF1 binding site), -75A/G (in the proximal Pit-1 binding site) and -57G/T (in the VDR binding site), induced a different luciferase activity when transfected in a rat pituitary cell line. The presence of a G instead of an A at position -75 induced a more than two-fold reduced activity (p<0.0001). In accordance with this findings the electrophoretic mobility shift assay demonstrated a reduced affinity of the -75G for the pituitary transcription factor Pit-1. Despite the strong effect of this polymorphism in vitro, the -75G variation was not associated to an impairment of the GH secretion in vivo.

A novel deletion in the GH1 gene including the IVS3 branch site responsible for autosomal dominant isolated growth hormone deficiency.

CONTEXT: The majority of mutations responsible for isolated GH type II deficiency (IGHD II) lead to dominant negative deleteriously increased levels of the GH1 exon 3 skipped transcripts. OBJECTIVE: The aim of this study was the characterization of the molecular defect causing a familial case of IGHD II. PATIENTS: A 2-yr-old child and her mother with severe growth failure at diagnosis (-5.8 and -6.9 sd score, respectively) and IGHD were investigated for the presence of GH1 mutations. RESULTS: We identified a novel 22-bp deletion in IVS3 (IVS3 del+56-77) removing the putative branch point sequence (BPS). Analysis of patients' lymphocyte mRNA showed an excess exon 3 skipping. The mutated allele transfected into rat pituitary cells produced four differently spliced products: the exon 3 skipped mRNA as the main product and lower amounts of the full-length cDNA and of two novel mRNA aberrant isoforms, one with the first 86 bases of exon 4 deleted and the other lacking the entire exon 4. A mutagenized construct lacking exclusively the 7 bp of the BPS only generated the exon 4 skipped and the full-length isoforms. The presence of the full-length transcript in the absence of the canonical BPS points to an alternative BPS in IVS3. CONCLUSION: The IVS3 del+56-77 mutation, causing IGHD II in this family, has two separate effects on mRNA processing: 1) exon 3 skipping, analogous to most described cases of IGHD II, an effect likely caused by the reduction in size of the IVS3, and 2) partial or total exon 4 skipping, as a result of the removal of the BPS.

Osteopontin gene haplotypes correlate with multiple sclerosis development and progression.

Osteopontin (OPN) is an inflammatory cytokine highly expressed in multiple sclerosis (MS) plaques. In a previous work, we showed that four OPN polymorphisms form three haplotypes (A, B, and C) and that homozygotes for haplotype-A display lower OPN levels than non-AA subjects. In this work, we evaluated the distribution of these OPN haplotypes in 425 MS patients and 688 controls. Haplotype-A homozygotes had about 1.5 lower risk of developing MS than non-AA subjects. Clinical analysis of 288 patients showed that AA patients displayed slower switching from a relapsing remitting to a secondary progressive form and milder disease with slower evolution of disability. MS patients displayed increased OPN serum levels, which were partly due to the increased frequency of non-AA subjects. Moreover in AA patients, OPN levels were higher than in AA controls and similar to those found in both non-AA patients and controls, which suggests a role of the activated immune response. These data suggest that OPN genotypes may influence MS development and progression due to their influence on OPN levels.

HLA-multiple sclerosis association in continental Italy and correlation with disease prevalence in Europe.

The association with HLA-DRB1 alleles was tested in 609 Continental Italian MS patients and 836 controls. The phenotype frequency of DRB1*15 in the patients was significantly higher (0.316 vs. 0.112; p(c)<10(-6); Odds Ratio (OR)=3.64) with no dose effect. DRB1*10 was also significantly increased (OR=2.19; p(c)=0.047) and DRB1*07 decreased (OR=0.60; p(c)=1.3 x 10(-3)) independently of DR15 and of each other. We did not detect an influence of the DR phenotype on disease course, age at onset/diagnosis, gender or familiarity. No association with Class I was detected in a random subset of patients and controls. A comparison of the HLA association data in Northern and Southern European populations shows a parallel between disease prevalence and DR15 frequency.

Refining the linkage analysis on chromosome 10 in 449 sib-pairs with multiple sclerosis.

Genome-wide screens for linkage in multiplex families with multiple sclerosis (MS) from United Kingdom, Sardinia, Italy and the Nordic countries (Denmark, Finland, Norway and Sweden) have each shown suggestive or potential linkage on chromosome 10. The partially overlapping regions identified by these studies encompass around 60 cM of the chromosome. In order to explore this region further, we typed 13 microsatellite markers in the same 449 families originally studied in the individual screens. This additional genotyping increased the information extraction in the region from 52% to 79% and revealed increased support for linkage (MLS 2.5) peaking at 10p15.

A whole genome screen for linkage disequilibrium in multiple sclerosis performed in a continental Italian population.

We have systematically screened the genome for evidence of linkage disequilibrium (LD) with multiple sclerosis (MS) by typing 6000 microsatellite markers in case-control and family based (AFBAC) cohorts from the Italian population. DNA pooling was used to reduce the genotyping effort involved. Four DNA pools were considered: cases (224 Italian MS patients), controls (231 healthy Italians), index (185 index cases from trio families) and parents (the 370 parents of the patient included in the Index pool), respectively. After refining analysis of the most promising 14 markers to emerge from this screening process, only marker D2S367 retained evidence for association.

Genetic interaction of CTLA-4 with HLA-DR15 in multiple sclerosis patients.

Multiple sclerosis is a chronic inflammatory disease of the central nervous system with a genetic component. Until now, the more consistent association with the disease is found with the major histocompatibility complex, especially HLA-DRB1*1501-DQB1*0602 haplotype. In this report, we demonstrate the interaction of Cytotoxic T Lymphocyte-associated antigen 4 (CTLA-4 [CD152]) gene with DRB1*15 haplotype in multiple sclerosis genetic susceptibility. Our data were obtained from two European independent family-based studies including 610 multiple sclerosis family trios. Ann Neurol 2003;54:119-122

CD45 and multiple sclerosis: the exon 4 C77G polymorphism (additional studies and meta-analysis) and new markers.

We re-evaluated the association with multiple sclerosis (MS) of the C77G splicing regulatory variation in the CD45 gene and screened for new mutations the three alternatively spliced exons (#4, 5 and 6). No association with C77G was detected in two groups of patients (total=448) and controls (total=559) from Northern and Southern Italy. When excluding the first published study indicating a positive association, a meta-analysis of the five further studies conducted to date (including the present one) led to a non-significant combined odds ratio (OR) of 1.11. None of the four newly identified nucleotide substitutions, namely C77T (Pro59Pro) in exon 4, G69C (Asp121His) in exon 5, T127A (Ile187Asn) and A138G (Thr191Ala) in exon 6, was significantly associated to MS.

Prolactin and prolactin receptor gene polymorphisms in multiple sclerosis and systemic lupus erythematosus.

Genes encoding for prolactin (PRL) and its receptor (PRLR) are possible candidates for multiple sclerosis (MS) and systemic lupus erythematosus (SLE) susceptibility. In fact: (1) a prolactin secretion dysfunction has been described in several autoimmune diseases including SLE and MS and their animal models; (2) both PRL and PRLR are structurally related to members of the cytokine/hematopoietin family and have a role in the regulation of the immune response; and (3) both PRL and PRLR genes map in genomic regions that showed linkage with autoimmunity. Prolactin maps on chromosome 6p, about 11-kb telomeric to HLA-DRB1 and PRLR in 5p12-13, which revealed evidence of linkage with MS in different populations. To evaluate a possible role of these two genes in SLE and MS we performed an association study of 19 PRL and PRLR single nucleotide polymorphisms (SNPs). These were directly searched by DHPLC in a panel of SLE and MS patients and selected from databases and the literature. The SNP allele frequencies were determined on patient and control DNA pools by primer-extension genotyping and HPLC analysis. Moreover a panel of HLA typed SLE and control individuals were individually genotyped for the PRL G-1149T polymorphism previously described to be associated with SLE. No statistically significant difference in the allele distribution was observed for any of the tested variations.

A collaborative European search for non-DQA1*05-DQB1*02 celiac disease loci on HLA-DR3 haplotypes: analysis of transmission from homozygous parents.

The HLA-DQA1*05 with DQB1*02 alleles are a major risk factor for celiac disease (CD). To search for additional human leukocyte antigen (HLA) risk factors, we looked on the DR3-DQ2 risk haplotype, selected because it carries both DQ risk alleles in cis and is the more represented among CD patients. In a European consortium, we identified 109 families with a parent homozygous for DQA1*05-DQB1*02. We typed ten microsatellites in the extended HLA complex, and applied the homozygous-parent transmission disequilibrium test (HPTDT) and extended-TDT to transmissions from homozygous parents. These methods eliminate confounding due to linkage disequilibrium between candidate disease loci and the known risk factor DQA1*05-DQB1*02, and are favorable when sufficient families are available. We did not find evidence of association with any single marker or allele, although weak evidence for additional risk was observed, represented by preferential transmission of six adjacent markers. We tested the largest ever reported HPTDT population in CD, providing unprecedented power. We did not find significant evidence of additional risk-modifying factors on the DR3 haplotype, independent of DQA1*05-DQB1*02, although a weak tendency was observed for the B8-DR3 haplotype. This effect should be tested in large populations with significant representations of both B8-DR3 and non-B8 DR3 haplotypes.

Genetics of multiple sclerosis: linkage and association studies.

Multiple sclerosis (MS) is a demyelinating autoimmune disease of the central nervous system caused by an interplay of environmental and genetic factors. The only genetic region that has been clearly demonstrated by linkage and association studies to contribute to MS genetic susceptibility is the human leukocyte antigen (HLA) system. The majority of HLA population studies in MS have focused on Caucasians of Northern European descent, where the predisposition to disease has been consistently associated with the class II DRB1*1501-DQA1*0102-DQB1*0602 haplotype. A positive association with DR4 was detected in Sardinians and in other Mediterranean populations. Moreover DR1, DR7, DR11 have been found to be protective in several populations. Systematic searches aimed at identifying non-HLA susceptibility genes were undertaken in several populations by means of linkage studies with microsatellite markers distributed across the whole genome. The conclusion of these studies was that there is no major MS locus, and genetic susceptibility to the disease is most likely explained by the presence of different genes each conferring a small contribution to the overall familial aggregation. The involvement of several candidate genes was tested by association studies, utilizing either a population-based (case control) or a family-based (transmission disequilibrium test) approach. Candidate genes were selected mainly on the basis of their involvement in the autoimmune pathogenesis and include immunorelevant molecules such as cytokines, cytokine receptors, immunoglobulin, T cell receptor subunits and myelin antigens. With the notable exception of HLA, association studies met only modest success. This failure may result from the small size of the tested samples and the small number of markers considered for each gene. New tools for large scale screening are needed to identify genetic determinants with a low phenotypic effect. Large collaborative studies are planned to screen several thousands of patients with MS with several thousands of genetic markers. The tests are increasingly based on the DNA pooling procedure.