The Prince by Niccolo Machiavelli

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ORIGINAL RESEARCH ARTICLE
published: 22 April 2013 doi: 10.3389/fgene.2013.00057

Down syndrome related muscle hypotonia: association with COL6A3 functional SNP rs2270669 Arpita Dey 1 ‡ , Krishnendu Bhowmik 2 ‡ , Arpita Chatterjee 1 † , Pit Baran Chakrabarty 2 † , Swagata Sinha 1 and Kanchan Mukhopadhyay 1 * 1 2

Manovikas Biomedical Research and Diagnostic Centre, Kolkata, West Bengal, India Anatomy Department, Calcutta Medical College, Kolkata, West Bengal, India

Edited by: Alexander K. Murashov, East Carolina University, USA Reviewed by: Dianne M. Walters, East Carolina University, USA Jitka A. Virag, Brody School of Medicine, USA Margarita Glazova, Russian Academy of Science, Russia *Correspondence: Kanchan Mukhopadhyay , Manovikas Biomedical Research and Diagnostic Centre, 482 Madudah, Plot I-24, Sector-J, Eastern Metropolitan Bypass, Kolkata 700107 West Bengal, , India. e-mail: kanchanmvk@yahoo.com † Present address: Arpita Chatterjee, National Brain Research Centre, Manesar, Gurgaon, Haryana, India; Pit Baran Chakrabarty , Anatomy Department, Bankura Sammilani Medical College, Bankura, West Bengal, India. ‡

Arpita Dey and Krishnendu Bhowmik have contributed equally to this work.

Down syndrome (DS), the principal cause for intellectual disability, is also associated with hormonal, immunological, and gastrointestinal abnormalities. Muscle hypotonia (MH) and congenital heart diseases (CHD) are also frequently observed. Collagen molecules are essential components for maintaining muscle integrity and are formed by the assembly of three chains, alpha 1–3. The type VI collagen is crucial for cardiac as well as skeletal muscles. The COL α1 (VI) and α2 (VI) chains are encoded by genes located at the 21st chromosome and are expected to have higher dosage in individuals with DS. The α 3 (VI) chain is encoded by the COL6A3 located at the chromosome 2. We hypothesized that apart from COL6A1 and COL6A2, COL6A3 may also have some role in the MH of subjects with DS. To find out the relevance of COL6A3 in DS associated MH and CHD, we genotyped two SNPs in COL6A3, rs2270669 and rs2270668, in individuals with DS. Subjects with DS were recruited based on the Diagnostic and Statistical Manual for Mental Disorders-IV and having trisomy of the 21st chromosome. Parents of individuals with DS and ethnically matched controls were enrolled for comparison. Informed written consent was obtained for participation. Peripheral blood was used for isolation of genomic DNA. Target genetic loci were studied by DNA sequence analysis. Data obtained was subjected to population – as well as family-based statistical analysis. rs2270668 was found to be non-polymorphic in the studied population. rs2270669 showed significant association of the “C” allele and “CC” genotype with DS probands having MH (P = 0.02). Computational analysis showed that rs2270669 may induce structural and functional alterations in the COL α3 (VI). Interaction of COLα3 (VI) with different proteins, crucial for muscle integrity, was also noticed by computational methods. This pioneering study on COL6A3 with DS related MH thus indicates that rs2270669 “C” could be considered as a risk factor for DS related MH. Keywords: Down syndrome, muscle hypotonia, congenital heart disease, functional SNP COL6A3 ,

INTRODUCTION
Down syndrome (DS), the most common genetic cause for intellectual disability is characterized by the presence of one extra copy of the human chromosome 21 (Hsa21) (Roizen and Patterson, 2003; Rachidi and Lopes, 2007). The commonly accepted hypothesis to correlate the extra Hsa21 with DS pathophysiology is overexpression of genes present in the Hsa21 (Chou et al., 2008). However, changes in the expression of other euploid genes, possibly due to the presence of an extra Hsa21, were also speculated to contribute to the phenotypic variations in DS (Chou et al., 2008). Abbreviations: AV, atrio-ventricular; BM, Bethlem myopathy; CEU, Caucasians from Utah with ancestry...
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