Jasmin Roohi

3rd Year Medical Student

Department: SOM

Graduate Program: Genetics

Advisor: Dr. Eli Hatchwell

Abstract:

Title: Identification of Potential Candidate Genes in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a severe developmental disorder of the central nervous system characterized by impairments in social interaction, communication, and range of interests and behaviors. The syndrome’s prevalence is estimated to be as high as 1 in 150 American children yet its etiology remains largely unknown. Examination of observed cytogenetic variants in individuals with ASD may identify genes involved in its pathogenesis. A genetic study of the syndrome was undertaken in a clinically well-characterized cohort of 92 individuals with ASD. Initial screens of this group for potential candidate genes utilized array-based comparative genomic hybridization (aCGH) and karyotype.

aCGH identified several copy number variations (CNVs) in our patient population. Of particular interest was a paternally inherited chromosome 3 CNV in 3 subjects: a deletion in 2 siblings and a duplication in a third, unrelated individual. These variations were validated with fluorescence in situ hybridization and the endpoints further delineated using a custom fine tiling oligonucleotide array. PCR products unique to the rearrangements were amplified and sequence analysis revealed the variations to have resulted from Alu Y-mediated unequal recombinations interrupting contactin 4 (CNTN4). CNTN4 plays an essential role in the formation, maintenance, and plasticity of neuronal networks. Disruption of this gene is known to cause developmental delay and mental retardation.

Karyotype identified an apparently balanced de novo translocation between chromosomes 2 and 9 [46,XY,t(2;9)(p13;p24)] in another subject. Molecular characterization of the rearrangement revealed direct interruption of the RAB11 family interacting protein 5 (RAB11FIP5) gene. RAB11FIP5 is a Rab effector involved in protein trafficking from apical recycling endosomes to the apical plasma membrane. It is ubiquitously expressed and reported to contribute to both neurotransmitter release and neurotransmitter uptake at the synaptic junction. The protein might also participate in transcytosis essential for proper neuron functioning. Detailed analysis of the rearrangement breakpoints suggests that the reciprocal translocation may have formed secondary to incorrect repair of double strand breaks (DSBs) by nonhomologous end-joining (NHEJ).

These findings suggest that mutations affecting CNTN4 or RAB11FIP5 may be relevant to ASD pathogenesis. Approximately 1200 individuals with ASD were examined for subtle mutations of these genes with 454 sequencing. Several interesting mutations were detected, including stop codons. Future plans include confirmation of these sequence changes. In addition, other potential candidate genes affected by CNVs in our cohort will be examined further.

Publications:
(MSTP-supported publications indicated with an *)

*Herbert MR, Russo JP, Yang S, Roohi J, Blaxill M, Kahler SG, Cremer L, Hatchwell E. (2006). Autism and environmental genomics. Neurotoxicology. 5:671-84.

*Roohi J, Cammer M, Montagna C, Hatchwell E. An Improved Method for Generating BAC DNA Suitable for FISH. Cytogenet Genome Res. In press.

*Roohi J, Tegay DH, Pomeroy JC, Burkett S, Stone G, Stanyon R, Hatchwell E. (2008). A de novo apparently balanced translocation [46,XY,t(2;9)(p13;p24)] interrupting RAB11FIP5 identifies a potential candidate gene for autism spectrum disorder. Am J Med Genet B Neuropsychiatr Genet.

*Roohi J, Montagna C, Tegay DH, Palmer LE, Devincent C, Pomeroy JC, Christian SL, Nowak N, Hatchwell E. (2008). Disruption of Contactin 4 in 3 Subjects with Autism Spectrum Disorder. J Med Genet.

*Tegay DH, Lane AH, Roohi J, Hatchwell E. (2007). Contiguous gene deletion involving L1CAM and AVPR2 causes X-linked hydrocephalus with nephrogenic diabetes insipidus. Am J Med Genet A. 143(6):594-8.