患儿在6～8个月时生长发育正常，多数病例表现以近端为主的严重肌无力下肢重于上肢多发性微小肌阵挛呼吸肌以及吞咽肌不受累括约肌功能正常SMA-Ⅲ型也称为Wohlfart-Kugelberg-Welander综合征或轻度SMA，是SMA中表现最轻的一类。
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