5 research outputs found

    Functional Properties of Rare Missense Variants of Human <i>CDH13</i> Found in Adult Attention Deficit/Hyperactivity Disorder (ADHD) Patients

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    <div><p>The <i>CDH13</i> gene codes for T-cadherin, a GPI-anchored protein with cell adhesion properties that is highly expressed in the brain and cardiovascular system. Previous studies have suggested that <i>CDH13</i> may be a promising candidate gene for Attention Deficit/Hyperactivity Disorder (ADHD). The aims of this study were to identify, functionally characterize, and estimate the frequency of coding <i>CDH13</i> variants in adult ADHD patients and controls. We performed sequencing of the <i>CDH13</i> gene in 169 Norwegian adult ADHD patients and 63 controls and genotyping of the identified variants in 641 patients and 668 controls. Native and green fluorescent protein tagged wild type and variant CDH13 proteins were expressed and studied in CHO and HEK293 cells, respectively. Sequencing identified seven rare missense <i>CDH13</i> variants, one of which was novel. By genotyping, we found a cumulative frequency of these rare variants of 2.9% in controls and 3.2% in ADHD patients, implying that much larger samples are needed to obtain adequate power to study the genetic association between ADHD and rare CDH13 variants. Protein expression and localization studies in CHO cells and HEK293 cells showed that the wild type and mutant proteins were processed according to the canonical processing of GPI-anchored proteins. Although some of the mutations were predicted to severely affect protein secondary structure and stability, no significant differences were observed between the expression levels and distribution of the wild type and mutant proteins in either HEK293 or CHO cells. This is the first study where the frequency of coding <i>CDH13</i> variants in patients and controls is reported and also where the functional properties of these variants are examined. Further investigations are needed to conclude whether <i>CDH13</i> is involved in the pathogenesis of ADHD or other conditions.</p></div

    Schematic description of the CDH13 proteins expressed in CHO and HEK293 cells.

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    <p>CDH13 was expressed with or without a C-terminal tGFP tag in HEK293 and CHO cells, respectively. The location of the identified variants is also shown (A). According to the general model of processing of GPI anchored proteins in the ER, a C-terminal transmembrane domain is cleaved off and is then replaced by a GPI anchor. The protein with the attached GPI anchor is then directed to the external side of the plasma membrane (B). Wild type and variant CDH13 proteins were expressed on the cell membrane in HEK293 and CHO cells. In HEK293 cells, the C-terminal GFP tag of the GFP-CDH13 fusion proteins was cleaved off as a result of GPI anchoring at the c- terminal of CDH13 and the fully processed protein was subsequently transferred to the cell membrane.</p

    Frequency of <i>CDH13</i> variant alleles identified in Norwegian adult patient and control groups.

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    <p>Seven <i>CDH13</i> variants were identified in the sequencing study, three of which were only detected in patients. All variants were genotyped in a larger sample. Two-tailed P-values for genotype frequencies were calculated by Fisher’s exact test in a 2×2 contingency table.</p

    <i>In silico</i> analysis of the effect of CDH13 variants.

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    <p>The analysis was based on the protein sequence. SIFT scores below 0.05 were considered damaging. I-mutant-3.0 predicted the effects of the variants on protein stability by calculating the unfolding Gibbs free energy value of the mutant proteins minus that of the wild type protein (ΔΔG = ΔG mutant – ΔG wild type), given in kcal/mol. A negative change indicates decreased stability. The reliability index (RI) for a large decrease (ΔΔG<−0.5) ranged from 0–10. For the G113R* a reliability index for a neutral stability change was given. Ternary classification (SVM3) −0.5< = ΔΔG< = 0.5 corresponds to neutral stability, ΔΔG<−0.5 to large decrease of stability and ΔΔG >0.5 to a large increase of stability.</p

    CDH13 stained CHO cells expressing wild type and variant CDH13 on the plasma membrane.

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    <p>Cells were permeabilised before staining. A) Mock transfected cells, B) wild type CDH13, C) A376T, D) G113R, E) I585V, F) L643R, G) N39S, H) R174W, I) V112I. Wild type and variant CDH13 proteins were expressed on the cell membrane. Mock transfected cells did not express CDH13.</p