A loss‐of‐function mutation in the FTSJ1 gene causes nonsyndromic X‐linked mental retardation in a japanese family

Mental retardation (MR) is a common trait, affecting ∼2–3% of individuals in the general population. Although the etiology of MR remains largely unknown, genetics apparently play a major role. Recent molecular studies of X‐linked form of MR in European and North American countries have revealed 24 nonsyndromic X‐linked mental retardation (NS‐XLMR) genes including FTSJ1 , a human homolog of the Escherichia coli 2 ′‐ O ‐rRNA methyltransferase FtsJ/RrmJ gene. Here we identified a novel FTSJ1 mutation in an XLMR family through mutation screening of a cohort of 73 unrelated Japanese male probands with MR. Sequence analysis of the proband and his mother revealed a G > A substitution at the consensus for the donor splicing site in intron 8 (c.571 + 1G > A) of FTSJ1 . This mutation prevented the removal intron 8 from the pre‐mRNA, thereby leading to a frameshift in the mutant FTSJ1 mRNA and resulting in a premature termination in exon 9. Quantitative RT‐PCR showed a significant reduction of mutant FTSJ1 mRNA in the patient's lymphoblast cells, which was restored by treatment with cycloheximide, a potent inhibitor of nonsense‐mediated mRNA decay (NMD). Therefore, mRNAs carrying this mutation are likely subject to degradation by NMD. Together, loss‐of‐function of FTSJ1 may be a mechanism for the cognitive dysfunction observed in this family. Our study also suggested that the FTSJ1 mutation probably accounts for XLMR in Japanese at a similar frequency (1–2%) as in Europeans. © 2007 Wiley‐Liss, Inc.