Aim: FOXP2 was described as the first gene relevant to human speech and language disorders. The main objective of this study was to compare the distribution of FOXP2 gene polymorphisms between patients with speech sound disorder and healthy controls.
Methods: Five FOXP2 polymorphisms, rs923875, rs2396722, rs1852469, rs17137124 and rs1456031, were analyzed in 150 patients with speech sound disorder according to DSM-IV, as well as in 140 healthy controls. Coding exons for key domains of FOXP2 were also sequenced in all the patients.
Results: Significant differences in the genotype (P = 0.001) and allele (P = 0.0025) frequencies of rs1852469 (located 5′ upstream of the ATG initiator codon) were found between patients and controls. The excess of the T allele in the patients group remained significant after Bonferroni correction (P = 0.0126). Further investigations revealed a risk haplotype: rs2396722T/+rs1852469T. Our screening of key domains did not detect any point mutations in this sample. But we detected heterozygous triplet deletion of the glutamine-encoding region of exon 5 that alter FOXP2 protein sequence in five probands. These changes are predicted to yield a polyglutamine tract reduction from 40 to 39 consecutive glutamines.
Conclusions: Our data support a possible role of FOXP2 in the vulnerability to speech sound disorder, which adds further evidence to implicate this gene in speech and language functions.