The fragile X mental retardation (FMR) syndrome is the largest source of inherited mental retardation. The syndrome is usually caused by the transcriptional silencing of fragile X mental retardation gene (FMR-1). An 18 years old male wascompla띠ing of multiple toαh missing and abnormal facial profùe, of which signs were matemally dominant in his family. In the C)π。gene디c analysis the pa디ent and his parents did not show any discontinuity in the long arm end of X chromosome, but in the PCR produαs targeω19 the CGG repeat sequence in the 5' untranslated region of FMR gene both the patient'’ s and his mother' s gDNAs produced a normal and an extra bands, sized about 400 and 800 bps, respectively, while the his father' s gDNA produced only one normal band, sized about 400 bps. 까1US ， we suppose that the pa디.ent has heterozygotic alleles of FMR gene inherited matemally, and that the patient s FMR gene was in a premutated state relevant to the dentofacial abnormalities.