Characteristics of DYNC1H1 mutation spectrum
Of all the DYNC1H1 variants, exon 8 was found to be the mutational hot region with 24/58 (41.4%) families including 52 patients. Other clustered variants distributed in exon 4 (7/58 families with 7 patients, 12.1%), exon 5 (5/58 families with 19 patients, 8.6%), exon 6 (2/58 families with 3 patients, 3.4%), exon 13 (2/58 families with 3 patients, 3.4%), exon 14 (3/58 families with 3 patients, 5.2%), and exon 38 (2/58 families with 3 patients, 3.4%) (Fig.2). Several recurrent DYNC1H1 variants were reported, with c.1792C>T/p.R598C being the most common mutation (7/58 families with 10 patients, 12.1%). Others were c.751C>T/p.R251C (6/58, 10.3%), c.1953G>A/p.V612M (4/58 6.9%), c.2327C>T/p.P776L (3/58, 5.2%), c.917A>G/p.H306R (3/58, 5.2%) and c.3170A>G/p.Y970C (2/58, 3.4%). Interestingly, although c.1792C>T/p.R598C remains the most common mutation site related to neuromuscular diseases worldwide, it has not been reported in East Asian population yet. Instead, c.751C>T/p.R251C and c.2327C>T/p.P776L were more commonly reported in this region, which were found in 3/9 (33.3%) families and 2/9 (22.2%) families respectively.
Human DYNC1H1 protein is composed of 4646 amino acids (aa). Traditionally, it can be divided into the tail domain (0-1450 aa) and the motor domain (1450-4646 aa) according to its structural and functional characteristics. Of all the 39 DYNC1H1 variants, 27/39 (69.2%) were distributed in the tail domain and only 12/39 (30.8%) located in the motor domain, which was in correspondence with a previous study that mutations in the tail domain were more commonly related to motor-related disorders (Harms et al., 2012); (Rossor, Kalmar, Greensmith, & Reilly, 2012). More exactly, the DYNC1H1 protein is divided into several domains overlapping each other (Fig.3). Cases involved in our study revealed that the stem domain (53-1867 aa) contained the most amount of DYNC1H1 mutations (30/39, 76.9%), among which 18/39 (46.2%) were located in overlapping regions between stem and other domains, including DHC_N1 (242-832 aa), dynein intermediate chain (DIC)-binding domain (448-703 aa) and dynein intermediate light chain (DILC-binding) domain (651-802 aa). Mutations in other domains were relatively less frequent, including AAA2 (2180-2452 aa, 1/39, 2.6%), AAA3 (2556-2805 aa, 3/39, 7.7%), AAA4 (2899-3168 aa, 2/39, 5.1%), stalk (3189-3500 aa, 2/39, 5.1%) and the region between AAA4 and stalk (1/39, 2.6%). This result may be due to the fact that stem is the longest domain of DYNC1H1 located more closely to the N-terminal and overlaps many other regions. The detailed information of DYNC1H1mutation spectrum of patients with neuromuscular diseases was listed in table S1.