Autism spectrum disorders (ASD) are complex neurobehavioral disorders characterized by impaired social interaction and language development and by repetitive and stereotyped behaviors and interests. Twin and family studies indicate that genetic factors contribute to the susceptibility to ASD12. However, only 10–25% of cases of autism harbour identified chromosome abnormalities and/or present with genetic syndromes; the remaining 90% are idiopathic3. The male:female ratio of autism is approximately 4:1, implying the contribution of X chromosome genetic factors to the susceptibility of ASD.

Ribosomal protein L10 (RPL10), also called QM, is a highly conserved component of the large ribosome subunit (60s) that plays a crucial role in protein synthesis4. In humans, the RPL10 gene is located on chromosome Xq28, within a candidate region for ASD5. Recently, Klauck et al. identified two non-synonymous mutations, L206M and H213Q, in the C-terminal domain of RPL10 in four boys with ASD from two independent families. Furthermore, functional studies using yeast strains expressing human mutant RPL10 cDNAs exhibited aberrant ribosomal profiles, suggesting that the mutations may actually have an effect on translation6. High expression of RPL10 was observed in mouse hippocampus, an important brain site for learning and memory, which are impaired in autism7. To investigate whether RPL10 is involved in the pathogenesis of autism, we sequenced all RPL10 exons and quantified RPL10 mRNA level in patients with ASD and controls.

No non-synonymous mutations were detected in our cohort. The mRNA level of RPL10 was compared in four subgroups: male controls, male ASD, female controls and female ASD using two sets of primer pairs RPL10-A and RPL10-B (Figure 1). In controls, the transcript level of RPL10 was not significantly different between males and females (RPL10-A, U = 81, P = 0.7; RPL10-B, U = 61.5, P = 0.2). When cases and controls were compared, we did not observe any significant difference in RPL10 transcript levels (RPL10-A, U = 531, P = 0.2; RPL10-B, U = 607.5, P = 0.7). Female cases had a somewhat lower expression level of RPL10 compared with female controls (RPL10-A, U = 49, P = 0.06; RPL10-B, U = 47.5, P = 0.07). However, this trend disappeared after correction for multiple tests.

RPL10 belongs to the L10e family of ribosomal proteins and is hypothesized to be necessary for ribosome assembling and function. The identification of two missense mutations in highly conserved positions of RPL10 across species and functional studies in yeast strains expressing human wild-type/mutant RPL10 cDNAs suggested a novel aspect of disease mechanisms for autism – aberrant processes of ribosome biosynthesis and translation. To confirm these initial findings, we sequenced all RPL10 exons and flanking junctions in 141 ASD patients. No missense mutation was identified. We performed this study in European population as well as Klauck et al6 in order to exclude the possible sample stratification. Other factors, such as the sample size and highly genetic heterogeneity of ASD, should be considered when explaining the absence of RPL10 mutations in our sample. To further address the expression issue, mRNA transcript level of RPL10 was quantified in 48 patients and 27 controls using the method of SYBR Green quantitative PCR. Male controls showed the same transcript level of RPL10 compared with female controls, supporting the evidence that RPL10 is subject to X chromosome inactivation 12. No statistical significance in expression level was found between cases and controls, suggesting there was no difference in RPL10 expression between two groups. Taken together, our study could not confirm the association between RPL10 and ASD.

Three limitations should be considered in this study. First, our sample of patients screened for RPL10 (n = 141, 101 males and 40 females) was smaller compared to the previous study (n = 345, 268 males and 77 females)6. We had 56% of chance to detect at least one mutation in our sample. Our previous study indicated XCI profile could be a useful criteria to prioritize families for mutation screening of X-linked candidate genes in ASD, so we selected 88 individuals from the families with XCI skewing (≥ 70:30) and 53 patients from multiplex families for mutation screening of RPL108. However, we did not detect any functional mutations. Second, our mutation screening was restricted to exons and therefore was not appropriate to detect the presence of variants altering the expression of RPL10 in promoter regions or other regulatory regions. However, we recently performed a high-throughput genotyping of 91 patients from this sample using the Illumina human1M-duo beadchip, and we could not detect any genomic imbalance within or close to RPL10 (unpublished data). Thirdly, we performed the quantification of RPL10 mRNA level in B lymphoblastoid cell lines and therefore we could have missed alterations specific to brain. Thus, further studies on other bigger samples are warranted and the promoter regions and other regulatory regions should be investigated.

The present study did not find any non-synonymous mutations in our cohort, neither abnormal RPL10 transcript levels in ASD patients compared to controls, suggesting that RPL10 has no major effect on the susceptibility to ASD.

The authors declare that they have no competing interests.

XG carried out sequencing and quantitative PCR testing, and contributed to manuscript writing. RD performed the statistical analysis. FF aided in quantitative PCR testing. CMD, PC, and HGB aided in sample storage and preparations. CB, GN, HA, MR, ICG, SK, MCMS, CG and ML contributed to the sample collection. TB participated in the design of the study and manuscript writing.