OBJECTIVETo investigate the mutations in protein tyrosine phosphatase, nonreceptor-type 11 (PTPN11) gene in patients with Noonan syndrome (NS).

METHODSThree sporadic patients with NS were studied. Genomic DNAs were extracted from peripheral blood leukocytes. All 15 coding exons and their flanking intronic boundaries of the PTPN11 gene were amplified by polymerase chain reaction and followed by direct sequencing. DNAs from parents were sequenced in the corresponding region when the mutation was detected in their affected child. The identified mutation was screened in 100 healthy individuals for exclusion of polymorphism by restriction endonuclease digestion of the PCR products. Protein conservation analysis was performed among 10 species using an online ClustalW tool.

RESULTSDirect DNA sequence analysis identified a heterozygous 181G to A change in exon 3 of the PTPN11 gene in one patient, which resulted in the substitution of an aspartic acid residue by an asparagine at codon 61. The mutation was absent in his parents and 100 controls, and is located in a highly conserved amino acid site. No mutation in the coding region of PTPN11 gene was observed in the other two patients.

CONCLUSIONThe p.D61N mutation was reported previously in Caucasians and is a de-novo mutation in this patient. Our study further confirmed that the p.D61N is a pathogenic mutation for NS and consistent with the clinical diagnosis. Additional genes may be involved in the other two patients with NS, indicating high genetic heterogeneity of this disease.