Novel NOG mutation in Japanese patients with stapes ankylosis with broad thumbs and toes

Abstract

Human noggin (NOG) gene mutation causes multiple bony disorders showing up as stapes ankylosis with broad thumbs and toes (SABTT), proximal symphalangism (SYM1), multiple synostoses syndrome 1 (SYNS1), tarsal-carpal coalition syndrome (TCC) and brachydactyly type B2 (BDB2). These phenotypes are defined as NOG-related syndromes with the same mutation. Some of these syndromes feature stapes ankylosis as one of the several bony symptoms. Here, we report a Japanese family with conductive hearing loss due to congenital stapes ankylosis. This family showed multiple features and was diagnosed with SABTT. We performed analysis of the NOG in the family by direct sequence analysis, and found a novel NOG mutation: c.682 T> G (p.C228G). Our results and a review of previous cases with NOG protein conformation suggest that this mutated NOG protein lead to a change in antagonist activity in BMPs and/or a haploinsufficiency that likely impaired finger 2 structure.