A novel homozygous splicing mutation of the AGL gene in a Chinese patient with severe myopathy involvement of glycogen s
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LETTER TO THE EDITOR
A novel homozygous splicing mutation of the AGL gene in a Chinese patient with severe myopathy involvement of glycogen storage disease type IIIa Ying Li 1 & Xueliang Qi 2 & Wei Zhang 3 & Liqun Feng 1 & Yun Yuan 3 Received: 14 May 2020 / Accepted: 4 November 2020 # Fondazione Società Italiana di Neurologia 2020
Dear Editor-in-Chief, Glycogen storage disease type III is a rare metabolic disorder with autosomal recessive inheritance, caused by a deficiency of glycogen debranching enzyme (GDE), encoded by the AGL gene (1p21.2) [1, 2]. The GDE has two independent catalytic activities, 4-alpha-glucanotransferase (EC 2.4.1.25) and amylo-1,6-glucosidase (EC 3.2.1.33). Glycogen storage disease type III (GSD III) can be classified into four types (a, b, c, and d) according to the different affected organs and loss of different catalytic activities. In patients with GSD IIIa, liver involvement is predominant since birth, and it is seldom diagnosed in adults. Here, we report an adult with a novel homozygous splicing mutation of the AGL gene in a consanguineous family, who presented with severe myopathy.
Case report A 58-year-old man complained of general weakness for 13 years. He began walking independently at 3 years old; then, he lived a relatively normal life until he reported weakness when climbing stairs and squatting, and easily fell while walking at 45 years of age. His weakness usually worsened after movement, with mild muscle pain. He had a fracture after a fall at the age of 49. The situation progressively worsened until he had great difficulty in walking and rising from a seated * Yun Yuan [email protected] 1
Department of Neurology, Beijing Anzhen Hospital, Capital Medical University, Beijing 100029, China
2
Department of Neurology, The Second Affiliated Hospital of Nanchang University, Nanchang 330006, Jiangxi Province, China
3
Department of Neurology, Peking University First Hospital, Xishiku St 8#, Beijing 100034, China
position. At 55 years old, he developed upper limb weakness, due to which he could not turn over in the bed by himself. He denied sensory loss, cramping, dyspnea, or dysphagia. His parents were second cousins, and they were physically normal until they died. He had 2 brothers, 2 sisters, and a daughter, who were all physically normal. He had feet brachydactyly (Fig. 1). The strength of the masticatory muscles was mildly weakened. Muscle strength (MRC) was as follows: 4/5 in the masticatory muscles, neck, hands, and feet; 3/5 in the proximal arms and right thigh; and 2/5 in the left proximal leg. The muscle tone decreased without myotonia. There was diffuse muscle atrophy most pronounced in the proximal limbs. The tendon reflexes were decreased. Raised CK (862 U/L), CK-MB (37.6 ng/mL), myoglobin (238.5 ng/mL), aspartate transaminase (125 U/L), and total cholesterol (5.46 mmol/L) were detected. The levels of alanine transaminase, fasting blood glucose, and triglycerides were all in normal limits. However, a delayed fasting blood glucose test (9:30 AM) revealed a valu
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