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Saturday, May 9, 2009
Northwest Hall (Chicago Hilton)
12:00 PM
Background: The left inferior frontal gyrus (IFG) plays a fundamental role in communication. The left IFG is considered a classic speech center, to which focal lesions ablate speech (e.g., Alexander et al., 1990), and transcranial magnetic stimulation not only arrests overt speech (Thiel et al., 2005) but also covert speech (Aziz-Zadeh et al., 2005). Moreover, transcranial magnetic stimulation to the left IFG, in particular BA 44, disrupts volitional hand movement, such as that used in nonverbal communication and gesture (Uozumi et al., 2004).
Objectives: To examine the contribution of the left IFG to the autistic phenotype by examining a pair of monozygotic twins.
Methods: Participants were a pair of monozygotic twins recruited into a statewide sample of twin pairs in which one or both cotwins had received a community diagnosis on the autism spectrum. Both cotwins were screened with the SRS and SCQ at age 13;6, were assessed with the ADOS at 15;6, and underwent structural MRI at 17;8. Both twins, born from an unremarkable pregnancy, had received an unorthodox community diagnosis of “Asperger Syndrome with speech delay” at age three. When assessed during adolescence, the twins were comparable on two measures of nonverbal intelligence (Leiter International Performance Scale and Ravens Standard Progressive Matrices) and on two measures of receptive language (Test of Receptive Grammar and Peabody Picture Vocabulary Test). A re-test, two years later, on the Peabody Picture Vocabulary Test continued to show strong similarity between the two cotwins (Twin A PPVT standard score=108; Twin B PPVT standard score=111).
The twins differed dramatically on the Expressive Language Scale of the CELF-3. Twin A scored consistently lower on each of the three expressive subtests -- Recalling Sentences, Sentence Assembly, and Formulating Sentences – and received a significantly lower standard score (Twin A Expressive Language standard score=75, 90% CI=67-83; Twin B Expressive Language standard score=96, 90% CI=88-104).
Twin A exceeded by 1 point the SCQ “autism” cutoff, and Twin B exceeded by 1 point the SCQ “autism spectrum” cutoff. Twin A exceeded by 1 and 2 points, respectively, the “autism” cutoff on the ADOS Communication and Social Interaction scales, whereas Twin B exceeded by 1 point the “autism spectrum” cutoff for Social Interaction but missed by 1 point the “autism spectrum” cutoff for Communication. Finally, Twin A exceeded by 2 points the SRS cutoff for “severe” diagnoses, whereas Twin B missed by 6 points the SRS cutoff for “mild to moderate” diagnoses.
Results: Using a 3T GE-Signa MRI scanner, 3D T1-weighted, inversion-recovery prepped, fast-gradient echo images were acquired for each twin (TR=8.4 ms, TE=1.7 ms, TI=600ms, FOV=240x240mm, flip angle=10 degrees, 256x192 matrix, 124 axial slices, slice thickness=1.2mm). The right IFG for each twin was similar in sulcal contour. In contrast, the anterior ascending ramus and anterior horizontal ramus of the left IFG of Twin A formed more of a Y-shape, whereas Twin B's formed more of a J-shape.
Conclusions: This case study of monozygotic twins raises the possibility that epigenetic factors may influence the structure of the left IFG.
Objectives: To examine the contribution of the left IFG to the autistic phenotype by examining a pair of monozygotic twins.
Methods: Participants were a pair of monozygotic twins recruited into a statewide sample of twin pairs in which one or both cotwins had received a community diagnosis on the autism spectrum. Both cotwins were screened with the SRS and SCQ at age 13;6, were assessed with the ADOS at 15;6, and underwent structural MRI at 17;8. Both twins, born from an unremarkable pregnancy, had received an unorthodox community diagnosis of “Asperger Syndrome with speech delay” at age three. When assessed during adolescence, the twins were comparable on two measures of nonverbal intelligence (Leiter International Performance Scale and Ravens Standard Progressive Matrices) and on two measures of receptive language (Test of Receptive Grammar and Peabody Picture Vocabulary Test). A re-test, two years later, on the Peabody Picture Vocabulary Test continued to show strong similarity between the two cotwins (Twin A PPVT standard score=108; Twin B PPVT standard score=111).
The twins differed dramatically on the Expressive Language Scale of the CELF-3. Twin A scored consistently lower on each of the three expressive subtests -- Recalling Sentences, Sentence Assembly, and Formulating Sentences – and received a significantly lower standard score (Twin A Expressive Language standard score=75, 90% CI=67-83; Twin B Expressive Language standard score=96, 90% CI=88-104).
Twin A exceeded by 1 point the SCQ “autism” cutoff, and Twin B exceeded by 1 point the SCQ “autism spectrum” cutoff. Twin A exceeded by 1 and 2 points, respectively, the “autism” cutoff on the ADOS Communication and Social Interaction scales, whereas Twin B exceeded by 1 point the “autism spectrum” cutoff for Social Interaction but missed by 1 point the “autism spectrum” cutoff for Communication. Finally, Twin A exceeded by 2 points the SRS cutoff for “severe” diagnoses, whereas Twin B missed by 6 points the SRS cutoff for “mild to moderate” diagnoses.
Results: Using a 3T GE-Signa MRI scanner, 3D T1-weighted, inversion-recovery prepped, fast-gradient echo images were acquired for each twin (TR=8.4 ms, TE=1.7 ms, TI=600ms, FOV=240x240mm, flip angle=10 degrees, 256x192 matrix, 124 axial slices, slice thickness=1.2mm). The right IFG for each twin was similar in sulcal contour. In contrast, the anterior ascending ramus and anterior horizontal ramus of the left IFG of Twin A formed more of a Y-shape, whereas Twin B's formed more of a J-shape.
Conclusions: This case study of monozygotic twins raises the possibility that epigenetic factors may influence the structure of the left IFG.