A locus for nonspecific X-linked mental retardation mapped to a 22.3 cM region of Xp11.3-q22.3

X-Linked intellectual disability update 2022

Genes that are involved in the transcription process, mitochondrial function, glycoprotein metabolism, and ubiquitination dominate the list of 21 new genes associated with X-linked intellectual disability since the last update in 2017. The new genes were identified by sequencing of candidate genes (2), the entire X-chromosome (2), the whole exome (15), or the whole genome (2). With these additions, 42 (21%) of the 199 named XLID syndromes and 27 (25%) of the 108 numbered nonsyndromic XLID families remain to be resolved at the molecular level. Although the pace of discovery of new XLID genes has slowed during the past 5 years, the density of genes on the X chromosome that cause intellectual disability still appears to be twice the density of intellectual disability genes on the autosomes.

DIA1R is an X-linked gene related to Deleted In Autism-1

Background

Autism spectrum disorders (ASDs) are frequently occurring disorders diagnosed by deficits in three core functional areas: social skills, communication, and behaviours and/or interests. Mental retardation frequently accompanies the most severe forms of ASDs, while overall ASDs are more commonly diagnosed in males. Most ASDs have a genetic origin and one gene recently implicated in the etiology of autism is the Deleted-In-Autism-1 (DIA1) gene.

Methodology/Principal Findings

Using a bioinformatics-based approach, we have identified a human gene closely related to DIA1, we term DIA1R (DIA1-Related). While DIA1 is autosomal (chromosome 3, position 3q24), DIA1R localizes to the X chromosome at position Xp11.3 and is known to escape X-inactivation. The gene products are of similar size, with DIA1 encoding 430, and DIA1R 433, residues. At the amino acid level, DIA1 and DIA1R are 62% similar overall (28% identical), and both encode signal peptides for targeting to the secretory pathway. Both genes are ubiquitously expressed, including in fetal and adult brain tissue.

Conclusions/Significance

Examination of published literature revealed point mutations in DIA1R are associated with X-linked mental retardation (XLMR) and DIA1R deletion is associated with syndromes with ASD-like traits and/or XLMR. Together, these results support a model where the DIA1 and DIA1R gene products regulate molecular traffic through the cellular secretory pathway or affect the function of secreted factors, and functional deficits cause disorders with ASD-like symptoms and/or mental retardation.

Mental retardation and Xq12-Xq23: candidate loci for nonspecific mental retardation in the male population of the QinBa region

OBJECTIVES

The higher prevalence of nonspecific mental retardation (NSMR) presents an important socioeconomic and medical issue for families and the whole QinBa region in China. The obvious family aggregation and high heritability indicated that genetic causes play a role in the NSMR population in QinBa. This study discusses the relationship between Xq12-Xq23 region and NSMR in the QinBa area.

METHOD

We chose six short tandem repeats--DXS7132, DXS6979, DXS1191, DXS1230, DXS1072, and DXS6804, located in Xq12-Xq23--and analyzed the distribution difference of their alleles between the NSMR and control boys.

RESULTS

A significant allele distribution difference was found between NSMR and control boys (all P<0.05) for DXS7132, DXS1191, DXS1230, DXS1072, and DXS6804 but not for DXS6979.

CONCLUSION

Our results suggest that Xq12-Xq23 may be the candidate region where there are one or more loci, linked to NSMR in the QinBa region. Further study needs to be carried out for locating the gene responsible for NSMR in this region and a larger sample size and more genetic markers are needed.