Spinal muscular atrophy with lower extremity predominance (SMA-LED) is an autosomal dominant disorder. Since SMA-LED affects lower motor neurons, the disease is characterized by weakness and atrophy of lower limb muscles. We present a familial case series of SMA-LED with upper motor neuron signs associated with a rare variant in DYNC1H1. The index case was referred to Pediatric Neurology at the age of two and half years, due to delayed mobility. The child was diagnosed with congenital vertical talus at birth, which was managed with serial bilateral casting and surgery. The delayed mobility was initially attributed to lower limb weakness secondary to prolonged periods of immobilization from casting of his lower limbs. He had a striking waddling gait and proximal muscle weakness on neurological assessment. He had lower motor neuron signs predominantly in his lower limbs that were in keeping with SMA-LED. Surprisingly, he also demonstrated a brisk crossed adductor response that was not in keeping with an isolated primary neuro-muscular disorder and suggested a mixed upper and lower motor neuron pathology. The inherited neuropathy gene panel revealed a heterozygous sequence change in the DYNC1H1 gene which was present in all affected family members. We present the first report of a familial case series of SMA-LED with upper motor neuron signs associated with an extremely rare variant in DYNC1H1: c.1808A > T (p.Glu603Val). As per the American College of Medical Genetics and Genomics (ACMG) guidelines for variant classification, we would recommend that this variant be reclassified as `Likely Pathogenic` due to matching 1 moderate (PM1-PM6) and ≥4 supporting (PP1-PP5) criteria in the reported case series.

Objective: To investigate the clinical features and gene variation characteristics of children with dynein cytoplasmic 1 heavy chain 1 (DYNC1H1) gene associated spinal muscular atrophy with lower extremity predominant (SMALED) 1. Methods: The clinical data of 4 SMALED1 children admitted to Peking University First Hospital from December 2018 to May 2021, who were found to have pathogenic variation of DYNC1H1 gene through genetic testing, except for other genes known to be related to motor retardation, were retrospectively summarized to analyze the phenotype and genotype characteristics. Results: There were 3 males and 1 female. The age of onset was 1 year, 1 day, 1 day and 4 months, respectively. The age of diagnosis was 4 years and 10 months, 9 months, 5 years and 9 months, and 3 years and 1 month, respectively. The clinical manifestations were muscle weakness and muscular atrophy of lower limbs, 2 cases with foot deformity, 1 case with early non progressive joint contracture, 1 case with hip dislocation and 1 case with mental retardation. De novo heterozygous missense variations in DYNC1H1 gene were found in all 4 children. According to the rating of American College of medical genetics and genomics, they were all possible pathogenic and pathogenic variations, with p.R598C, p.P776L, p.Y1109D variations had been reported, and p.I1086R variation had not been reported. Conclusions: For those with unexplained lower limb muscle weakness, muscle atrophy, joint contracture and foot deformity, upper limb motor ability related retention, with or without mental retardation, as well as the motor ability progresses slowly, it is necessary to consider the possibility of SMALED1 and the detection of DYNC1H1 gene when necessary. 目的： 探讨细胞质动力蛋白1重链1（DYNC1H1）基因相关下肢明显型脊髓性肌萎缩症（SMALED）1型患儿的临床特征及基因变异特点。 方法： 收集2018年12月至2021年5月北京大学第一医院收治的经基因检测发现DYNC1H1基因致病性变异的4例SMALED1型患儿病例资料，均除外已知与运动发育落后相关的其他基因变异，回顾性分析临床表现和基因型特点。 结果： 4例患儿中男3例、女1例，起病年龄分别为1岁、1日龄、1日龄和4月龄，确诊年龄分别为4岁10月龄、9月龄、5岁9月龄和3岁1月龄。临床表现均存在下肢为主的肌无力、肌萎缩，2例合并足畸形，1例合并早期非进展性关节挛缩，1例合并髋关节脱位，1例合并智力障碍。4例患儿均发现DYNC1H1基因新生杂合错义变异，根据美国医学遗传学与基因组学学会评级为可能致病和致病性变异，其中p.R598C、p.P776L、p.Y1109D变异已报道，p.I1086R变异尚未见文献报道。 结论： 对于婴儿期出现不明原因下肢肌无力、肌萎缩、关节挛缩及足畸形、上肢运动能力保留、伴或不伴智力障碍，运动能力缓慢进展者，需考虑SMALED1型可能，必要时完善DYNC1H1基因检测。.

The spinal muscular atrophies (SMA) affect lower motor neurons leading to important muscle atrophy and paralysis. Some cases of SMA affect mostly the lower limbs and are called autosomal dominant spinal muscular atrophy, lower extremity predominant (SMALED). So far, two genes have been identified to cause this phenotype, DYNC1H1 (SMALED1) and BICD2 (SMALED2). This pathology is rare, but patients exhibit classical features which should be recognised by physicians. We present two unrelated cases of SMALED2 with previously described c.320C>T BICD2 mutations. Our cases exhibit non-progressive weakness and atrophy of the lower limbs associated with contractures and unique muscle MRI findings suggestive of classical SMALED2. We also performed an extensive review of the literature to present the classical and atypical phenotypes of BICD2. Indeed, some features appear to be highly suggestive of the disease, including upper limb sparing, sparing of the adductors muscles on physical examination and MRI, congenital contractures and normal nerve conductions studies.