title: Further evidence of a primary, causal association of the PTPN22 620W variant with type 1 diabetes.
abstract: OBJECTIVE
  The minor allele of the nonsynonymous single nucleotide polymorphism (SNP) +1858C>T within the PTPN22 gene is positively associated with type 1 diabetes and other autoimmune diseases. Genetic and functional data underline its causal effect, but some studies suggest that this polymorphism does not entirely explain disease association of the PTPN22 region. The aim of this study was to evaluate type 1 diabetes association within this gene in the Sardinian population.
  
  
  METHODS
  We resequenced the exons and potentially relevant portions of PTPN22 and detected 24 polymorphisms (23 SNPs and 1 deletion insertion polymorphism [DIP]), 8 of which were novel. A representative set of 14 SNPs and the DIP were sequentially genotyped and assessed for disease association in 794 families, 490 sporadic patients, and 721 matched control subjects.
  
  
  RESULTS
  The +1858C>T variant, albeit rare in the general Sardinian population (allele frequency 0.014), was positively associated with type 1 diabetes (P(one tail) = 3.7 x 10(-3)). In contrast, the background haplotype in which this mutation occurred was common (haplotype frequency 0.117) and neutrally associated with disease. We did not confirm disease associations reported in other populations for non +1858C>T variants (rs2488457, rs1310182, and rs3811021), although they were present in appreciable frequencies in Sardinia. Additional weak disease associations with rare variants were detected in the Sardinian families but not confirmed in independent case-control sample sets and are most likely spurious.
  
  
  CONCLUSIONS
  We provide further evidence that the +1858C>T polymorphism is primarily associated with type 1 diabetes and exclude major contributions from other purportedly relevant variants within this gene.
authors.affiliation: Dipartimento di Scienze Biomediche, University of Sassari, Sassari, Italy.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Zoledziewska
authors.forename: Chiara
authors.initials: C
authors.lastname: Perra
authors.forename: Valeria
authors.initials: V
authors.lastname: Orrù
authors.forename: Loredana
authors.initials: L
authors.lastname: Moi
authors.forename: Paola
authors.initials: P
authors.lastname: Frongia
authors.forename: Mauro
authors.initials: M
authors.lastname: Congia
authors.forename: Nunzio
authors.initials: N
authors.lastname: Bottini
authors.forename: Francesco
authors.initials: F
authors.lastname: Cucca
mesh_terms: D000293:Adolescent; D000328:Adult; D001327:Autoimmune Diseases / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D004247:DNA / Q000097:blood / Q000235:genetics; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics*; D005787:Gene Frequency; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D007223:Infant; D007558:Italy; D015810:Linkage Disequilibrium; D011110:Polymorphism, Genetic; D020641:Polymorphism, Single Nucleotide; D054596:Protein Tyrosine Phosphatase, Non-Receptor Type 22 / Q000235:genetics*; D012016:Reference Values; D044465:White People / Q000235:genetics
chemical_list: D004247:DNA; C516765:PTPN22 protein, human; D054596:Protein Tyrosine Phosphatase, Non-Receptor Type 22