BackgroundAutism 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 FindingsUsing 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/SignificanceExamination 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.

Autism spectrum disorders (ASDs) are a group of commonly occurring, highly-heritable developmental disabilities. Human genes c3orf58 or Deleted In Autism-1 (DIA1) and cXorf36 or Deleted in Autism-1 Related (DIA1R) are implicated in ASD and mental retardation. Both gene products encode signal peptides for targeting to the secretory pathway. As evolutionary medicine has emerged as a key tool for understanding increasing numbers of human diseases, we have used an evolutionary approach to study DIA1 and DIA1R. We found DIA1 conserved from cnidarians to humans, indicating DIA1 evolution coincided with the development of the first primitive synapses. Nematodes lack a DIA1 homologue, indicating Caenorhabditis elegans is not suitable for studying all aspects of ASD etiology, while zebrafish encode two DIA1 paralogues. By contrast to DIA1, DIA1R was found exclusively in vertebrates, with an origin coinciding with the whole-genome duplication events occurring early in the vertebrate lineage, and the evolution of the more complex vertebrate nervous system. Strikingly, DIA1R was present in schooling fish but absent in fish that have adopted a more solitary lifestyle. An additional DIA1-related gene we named DIA1-Like (DIA1L), lacks a signal peptide and is restricted to the genomes of the echinoderm Strongylocentrotus purpuratus and cephalochordate Branchiostoma floridae. Evidence for remarkable DIA1L gene expansion was found in B. floridae. Amino acid alignments of DIA1 family gene products revealed a potential Golgi-retention motif and a number of conserved motifs with unknown function. Furthermore, a glycine and three cysteine residues were absolutely conserved in all DIA1-family proteins, indicating a critical role in protein structure and/or function. We have therefore identified a new metazoan protein family, the DIA1-family, and understanding the biological roles of DIA1-family members will have implications for our understanding of autism and mental retardation.

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