Evidence of motor axon or motor neuron damage in a Chinese patient with compound heterozygous MSTO1 variants
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LETTER TO THE EDITOR
Evidence of motor axon or motor neuron damage in a Chinese patient with compound heterozygous MSTO1 variants Yuqiong Jiao1 · Shenyi Kuang1 · Shilin Yang1 · Xiang Han1 Received: 23 October 2020 / Accepted: 30 October 2020 © Belgian Neurological Society 2020
Keywords MSTO1-related disease · Mitochondrial disorders · Motor axon damage · Motor neuron damage Dear Editor, MSTO1, a nuclear-encoded mitochondrial fusion gene, was first associated with a recessively inherited disorder in 2017 [1]. Phenotypic features of MSTO1-associated mitochondrial myopathy include early-onset motor delay, cerebral atrophy, elevated plasma creatine kinase (CK) and myopathic pattern on electromyography (EMG) [2, 3]. Here, we present a 14-year-old patient with MSTO1 variants and an unreported EMG feature. The research was approved by the local ethics committee, and informed consent was obtained from the patient’s parents. A 14-year-old Chinese girl born to non-consanguineous parents presented with severe motor delay (Fig. 1a). Her birth history was normal. She had difficulty in standing unaidedly at age 1 year. Subsequently, she suffered from muscle weakness and frequent falls, and was unable to walk independently until age 4 years. In addition, she performed poorly in study. Family history was negative. At age of 14 years, height was 150.00 cm ( T, p.T324I and c.22G > A, p.V8M (NM_018116). Sanger sequencing confirmed the paternal-origin of c.971C > T (Fig. 1e) and the maternalorigin of c.22G > A (Fig. 1f). To date, 29 patients with MSTO1 mutations (including the present case) have been reported. The phenotypic features were summarised in Supplementary Table 3 [1–7]. Our patient’s presentation overlapped well with the previous cases, including early-onset motor delay, elevated CK and cerebellar atrophy. In addition, she had a myogenic plus neuropathic pattern on EMG, and the latter has not been reported before. As we all know, mitochondrial disease can affect various tissues, especially the most energy-consuming tissues including peripheral nerves [8]. Most hereditary peripheral neuropathy is asymptomatic or subclinical [9]. Thus, our patient expands the phenotypic spectrum of MSTO1-related disease. c.971C > T has been reported to be pathogenic in two patients [1, 3]. c.22G > A has been considered to be a dominant mutation in a family with four patients [7]. However, the four patients had relative late onset, normal CK and cerebellar volume, which was inconsistent with previous publications. There was also a considerable phenotypic difference between the four patients. These facts argue against the real linkage between c.22G > A and their phenotypes. Actually, our case herein indicates that c.22G > A is a likely
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Fig. 1 Pedigree, Achilles tendon contracture, brain MRI and sequenogram of the identified variants. a Pedigree with the identified MSTO1 variants. b Contraction of Achilles tendon. c, d MRI (at age 14 years)
showed severe cerebellar and brain stem atrophy
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