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Several variants in exon 8 or 8a of <jats:italic>CACNA1C<\/jats:italic>, a gene encoding the \u03b1-subunit of voltage-gated Ca<jats:sup>2+<\/jats:sup> channels (Ca<jats:sub>v<\/jats:sub>1.2), are known to cause classical TS. We identified a p.R412M (exon 9) variant in an atypical TS case. The aim of this study was to examine the functional effects of <jats:italic>CACNA1C<\/jats:italic> p.R412M on Ca<jats:sub>V<\/jats:sub>1.2 in comparison with those of p.G406R. The index patient was\u00a0a 2-month-old female infant who suffered from a cardio-pulmonary arrest in association with prolonged QT intervals. She showed dysmorphic facial features and developmental delay, but not syndactyly. Interestingly, she also presented\u00a0recurrent seizures from 4\u00a0months. Genetic tests identified a novel heterozygous <jats:italic>CACNA1C <\/jats:italic>variant, p.R412M. Using heterologous expression system with HEK-293 cells, analyses with whole-cell patch-clamp technique revealed that p.R412M caused late Ca<jats:sup>2+<\/jats:sup> currents by significantly delaying Ca<jats:sub>V<\/jats:sub>1.2 channel inactivation, consistent with the underlying mechanisms of classical TS. A novel <jats:italic>CACNA1C<\/jats:italic> variant, p.R412M, was found to be associated with atypical TS through the same mechanism as p.G406R, the variant responsible for classical TS.<\/jats:p>","DOI":"10.1038\/s41598-022-23512-2","type":"journal-article","created":{"date-parts":[[2022,11,8]],"date-time":"2022-11-08T19:04:44Z","timestamp":1667934284000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Increased CaV1.2 late current by a CACNA1C p.R412M variant causes an atypical Timothy syndrome without syndactyly"],"prefix":"10.1038","volume":"12","author":[{"given":"Junichi","family":"Ozawa","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Seiko","family":"Ohno","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dario","family":"Melgari","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Qi","family":"Wang","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Megumi","family":"Fukuyama","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Futoshi","family":"Toyoda","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Takeru","family":"Makiyama","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Masao","family":"Yoshinaga","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hiroshi","family":"Suzuki","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Akihiko","family":"Saitoh","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tomohiko","family":"Ai","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Minoru","family":"Horie","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2022,11,8]]},"reference":[{"key":"23512_CR1","doi-asserted-by":"publisher","first-page":"19","DOI":"10.1016\/j.cell.2004.09.011","volume":"119","author":"I Splawski","year":"2004","unstructured":"Splawski, I. et al. 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