en Case & Review Case & Review <div style="text-align: justify;"><strong>Background:</strong> Methylmalonate-semialdehyde Dehydrogenase Deficiency (MMSDHD) is an uncommon autosomal recessive disorder. MMSDH is an enzyme encoded by the protein coding gene ALDH6A1 in humans.<br> <strong>Case Presentation: </strong>We present a 4-year-old boy with elevated liver enzymes, 3-hydroxyisobutyric aciduria (MMSDHD) and cardiac symptoms. He had a mutated ALDH6A1 gene, c.184c>G (p.Pro62Ala).<br> <strong>Conclusions: </strong>This is one of the rare case reports in the world and the first one in Iran that reports MMSDHD with cardiac disease.</div> Methylmalonate-semialdehyde dehydrogenase deficiency, Cardiac disease, ALDH6A1, 3-Hydroxyisobutyrate, 3-Hydroxypropionate 55 60 http://jpr.mazums.ac.ir/browse.php?a_code=A-10-285-1&slc_lang=en&sid=1 Morteza Alijanpour Aghamaleki 10031947532846003389 10031947532846003389 No Non-Communicable Pediatric Diseases Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran. Masoomeh Rezapour 10031947532846003390 10031947532846003390 No Department of Medical Sciences History, School of Traditional Medicine, Babol University of Medical Sciences, Babol, Iran. Kazem Babazadeh 10031947532846003391 10031947532846003391 No Non-Communicable Pediatric Diseases Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran. Hassan Zamani 10031947532846003392 10031947532846003392 No Department of Pediatrics, Shahid Modarres Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Faeze Aghajanpour faezeaghajanpour@yahoo.com 10031947532846003393 10031947532846003393 Yes Department of Statistics, Faculty of Mathematics and Statistics, University of Mazandaran, Babolsar, Iran.