Congenital muscular dystrophy caused by beta1,3-N-acetylgalactosaminyltransferase 2 gene mutation: Two case reports

INTRODUCTION

Congenital muscular dystrophy (CMD) refers to the primary and progressive myopathy that occurs at birth or within a few months after birth, usually causing considerable burden to the child and their families and society. The main clinical manifestations of CMD include premature myasthenia, hypodystonia, motor development retardation, and joint contracture with or without central nervous system involvement. The creatinase level tends to increase to varying degrees, myogenic damage can be seen on electromyography, and muscular dystrophy is the most common muscle pathology. Ge[1] reported that the prevalence rate of CMD in China was 0.017-0.083/100000. CMD is a group of hereditary diseases with strong heterogeneity caused by anti-dystroglycan (DG) deficiency. DG is a protein that is widely expressed in a variety of tissues, including the brain, Schwann cells of peripheral nerves, neuromuscular junction, muscle, liver, lung, and skin[2]. DG is cleaved into α-DG and β-DG after translation. The core structure of α-DG is dumbbellshaped, with a spherical C-terminal and an N-terminal at the two ends, respectively,while the middle is connected by a mucoprotein-like structure. α-DG undergoeslinked glycosylation, which rarely occurs[3]and then forms an antidystrophin-glycoprotein complex with β-DG. Then, it binds with ligands containing a laminin globular domain in the extracellular matrix, such as laminin, perlecan,agglutinin, axon protein, and pikacurin, to maintain muscle cell integrity[4], thus playing an important role in brain development[5]. α-DG has many glycosylation sites,short glycoprotein fragments, complex functions, and diverse pathogenic genes[6].Once the glycosylation of α-DG is impaired, it can trigger many pathophysiological processes, such as cell migration disorder[7] or α-dystroglycanopathy (α-DGP)[8].Recent studies[9] have shown that the gene located in 1q42.3 containing 64292 base pairs is one of its pathogenic genes, which encode beta1,3--acetylgalactosaminyltransferase2 (B3GALNT2). The deficiency of this enzyme can lead to the damage of α-DG glycosylation, consequently impairing the function of α-DG and affecting cell proliferation, migration, differentiation, and maintenance of tissue integrity, resulting in α-DGP[10]. Its pathogenic type was autosomal recessive inheritance.

互联网是以连接为目的导向的社会网络和复杂网络，互联网内容传播的本质其实是跨越平台建立人与人之间的连接。一切的交互都在产生连接行为，连接既是网络演化的手段也是网络演化的目标。内容创作的目标不再仅仅是获得用户的单次阅读，而是获得用户持续性的互动和稳定的认知连接。有了连接，才有用户和粉丝，社交分享量甚至比单次阅读量更加重要。没有一种连接是不可被替代的，替代的原则是连接得更强、更快、更紧、更美。[3]所有连接一旦建立，将不再满足于单一的连接形态，随着时间推移，它会不断叠加更为新鲜更为紧密的连接形态，从而形成连接的质变。

CASE PRESENTATION

Chief complaints

Case 2: Genetic examination showed that thecarried a compound heterozygous mutation (Figure 2). The mutation sites on the allele included c.261-2A>G(splicing) from the mother (Figures 2A and 2B) and c.979G>A (p.D327N) from the father (Figures 2C and 2D). The former was a missense mutation, and the latter was a nonsense mutation, which led to protein truncation.

Case 2: A 45-mo-old Chinese Han boy presented with delayed growth and development from childhood and an abnormal scalp in June 2019.

双馈风机等效惯性时间常数计算及转差率反馈惯量控制策略//刘皓明,任秋业,张占奎,李琰,许波峰//(17):49

History of present illness

Case 1: The child showed signs of developmental delay since childhood. He could raise his head at 5 mo, sit at 8 mo, walk alone at 1 year and 8 mo, and say the Chinese words for “mother” and “father” at 28 mo.

2009年到2010年，笔者在香港和上海两地，对香港跨界华人企业家在中国大陆的发展进行了人类学田野研究。以下两个人类学案例一步表明香港跨界华人企业家如何立足专业网络和互信关系，凭借跨界沟通能力和中国的政策制定者取得共识。从而确保成功的香港经验和商业模式能够在中国大陆社会主义市场经济的土壤中取得生存和发展。

History of past illness

Case 1: The patient had no special past history.

随着经济发展，中国对能源的需求高速增长，受国内资源条件的限制，未来中国原油在很大程度上将依赖进口。据中国海关进口原油来源地数据统计，目前中国原油进口区域中，中东、非洲、南美洲及俄罗斯位居前列，俄罗斯目前主要是管道和铁路运输，成本较高，其他国家和主要原油运输航线有着政治和海盗的风险，对中国能源安全造成威胁，如中东、马六甲海峡等。因此，从北极地区进口原油，建立多元化格局，保证原油充足供应是我国长期的战略选择。

（3）指事字的教学。汉字的演变是由形象逐渐向抽象发展的过程，教师在教授学生指事字时也应注意给学生提供有关汉字的来源，如在教“朱”字时，可告诉学生，“朱”字在的一横在木字之中，指的是木的中间，也就是树的中间，而这棵树刚好是松柏树，树中是赤红色的，所以朱字也就有红色的含义了。

税收执法部门有一定的裁定权，税收筹划能否真正地得到实施，还需要考虑当地税收部门的意见。因此，税收筹划人员在做税收筹划的过程中，应当加强与税务部门的交流，及时获取有用的税收信息，加强对征管的具体要求和限制的了解，可以降低税收筹划的违规风险。

Case 2: Meningocele was seen in the parietal and occipital region after birth, which then gradually healed.

Personal and family history

Case 1: The child was the fifth fetus and the second delivered by cesarean section at 38 wk of pregnancy. There was no significant family history.

Case 2: The child was the second fetus and delivered by full-term natural delivery.There was no significant family history.

Physical examination

Case 1: Physical examination revealed that the child could understand and respond to instructions, walked with “duck step”, and had no skin abnormalities or abnormal palpebral fissures. The bilateral pupils were round, equal in size, and sensitive to light reflex. The patient had no stiff neck, and no obvious heart, lung, and abdomen abnormalities. He had normal muscle strength of the extremities, bilateral biceps reflex, knee-tendon reflex, and active Achilles tendon reflex. He had low muscle tone and positive bilateral Babinski signs.

Case 2: The child could raise his head at 6 mo, sit alone at 12 mo, and walk at 24 mo.At the time of this visit, he still walked with a spastic gait. At present, he could pronounce a small number of disyllabic words such as the Chinese words for “father”and “mother”.

Case 2: Physical examination revealed that the child could understand and respond to instructions well, and walked with a spastic gait. An abnormal area of approximately 3 cm × 2 cm was visible in the parietal occipital area of the scalp; it was blue and purple in color, lacked hair growth, and showed no rupture, no tenderness, and no fluctuation. The bilateral eye fissure had no deformity, and bilateral pupils were round, equal in size, and sensitive to light reflex. There were no limitations of eye movement; no stiff neck; and no obvious abnormalities in the heart, lung, and abdomen. The muscle strength of the extremities was normal, and muscle tension was high. Bilateral biceps reflex, knee-tendon reflex, and Achilles tendon reflex were active,and bilateral Babinski signs were negative.

Laboratory examinations

Case 1: The leukoencephalopathy gene package (McKinnon) was used for sequencing,and the results demonstrated that thegene had a compound heterozygous mutation (Figure 1), and the allele mutations included c.1068dupT (p.D357_D358 delinsX) from the father (Figures 1A and 1B) and c.40G>C (p.G14R) from the mother(Figures 1C and 1D). The former was a nonsense mutation, which led to protein truncation, and the latter was a missense mutation.

At present, there are few reports about thegene causing CMD, and the relationship between genotype and phenotype is still not fully understood. In this paper, the pathogenic characteristics of this gene in two cases of α-DGP caused bygene mutation found in our hospital are summarized and discussed in view of previous reports.

Case 1: A 49-mo-old Chinese Han boy presented with abnormal walking posture in January 2019.

Imaging examinations

Case 1: At the age of 2 years and 4 mo, electromyography of the extremities was generally normal. Visual evoked potentials (Figure 3A) showed that both eyes were stimulated, each wave was well-differentiated, and P1 latency was significantly prolonged. Somatosensory evoked potentials (Figure 3B) showed that both upper limbs were stimulated, the cortical and surrounding waves were well-differentiated,and the latencies were roughly normal. Auditory evoked potentials (Figure 3C)suggested that bilateral ears were stimulated, the waveform of the left side was relatively poor, the latencies of the right III, IV, and V waves were prolonged. Head magnetic resonance imaging (MRI) showed cerebellar cortical cysts (Figure 4A),multiple flaky and linear equal/slightly long T1, long T2, and high fluid-attenuated inversion recovery signals around the bilateral ventricles of the brain (Figures 4B and 4C).

The authors have read the CARE Checklist (2016), and the manuscript was prepared and revised according to the CARE Checklist (2016).

制定智能化建筑用电节能设计时，一定要整体把握用电设施的布局分配、负荷容量及功率大小等信息，以此为基础，选择恰当、合理的节能供配电设备，保证用电设备正常工作的同时，最大限度地降低能耗的损失。

FINAL DIAGNOSIS

gene can be used as one of the candidate genes for screening CMD,cognitive development retardation, epilepsy, and multiple brain developmental malformations in infants.

TREATMENT

Both cases received coenzyme Q10 and levocarnitine. The giant arachnoid cyst in case 2 was resected.

OUTCOME AND FOLLOW-UP

Case 1

The patient could pronounce 2- to 3-syllable words, and his walking posture was improved over the course of the follow-up.

Case 2

At the latest follow-up visit, the child’s walking posture was improved compared to before, although language development did not significantly improve. He recovered well after resection of the giant arachnoid cyst, and the meningocele gradually selfhealed.

A total of 21 articles were found using the search key word ”” on the PubMed website, of which five articles were related to human CMD. The first article was published in 2013. The five articles included four pedigrees and seven sporadic patients. A total of 21 patients were reported, including the two patients in the present case report. Tables 1 and 2 present a summary of all these cases: (1) The nervous system was involved in all cases, and cognitive and motor developmental disorders were the most commonly encountered clinical symptoms (100%), followed by seizures(52.6%) and low muscle tension (64.3%); (2) Abnormal head MRI may be manifested as periventricular white matter lesion (81.3%), neuronal migration disorder (68.8%),brainstem and/or cerebellar dysplasia (56.3%), cerebellar cortical cyst (50%), and severe hydrocephalus (31.25%); (3) Muscle involvement was seen in 63.2% of patients,and the increased creatinase level ranged from 300 to 1740 U/L, which was even higher in patients with a more severe condition; and (4) Eye involvement occurred in 28.6% of the cases. The common symptoms were optic nerve atrophy and eye fissure deformities. In severe cases, glaucoma, cataract, and even blindness could be observed.

DISCUSSION

This study reports two cases of CMD caused bygene mutation. Both cases had an abnormal gait and significant delays in language development. Head MRI was performed for both children and revealed the presence of white matter lesions in the brain. The present report suggested that the cognitive language retardation and white matter lesions in CMD were caused bygene mutation. New symptoms of meningocele and giant arachnoid cyst were also encountered in one of our cases. To our knowledge, this is the first study to use electrophysiological examination of the audiovisual conduction pathway in children with this type of gene mutation. The findings suggest that even if audiovisual function was normal, the evoked audiovisual potential should be examined to investigate for potential abnormalities. The white matter lesions in case 2 were gradually absorbed and improved with age. He recovered well after surgical resection of the giant arachnoid cyst, and the meningocele gradually self-healed. These results suggested that some of the symptoms associated with the gene mutation might have a tendency to self-heal, which was consistent with the report of Hedberg[11]. Further studies are required to determine whether this is related to the peak age of gene expression. Both of the present cases had compound heterozygous mutations, the gene mutation sites were from their parents, and the mutations were compatible with autosomal recessive inheritance.

Case 1 had two compound heterozygous mutations in thegene; one of them was c.1068dupT (p.D357_D358delinsX), which was a nonsense (zero-effect)mutation that may lead to loss of gene function. The frequency in the normal population database was 0.00010, indicating that this was a low-frequency variation(PM2). The bioinformatics protein function prediction software packages SIFT,PolyPhen_2, and REVEL all predicted it as unknown. According to the American College of Medical Genetics and Genomics (ACMG) guidelines, the variation was preliminarily determined as a suspected pathogenic variation. The other was c.40G>C(p.G14R), which was a missense mutation. It was (-) in the normal population database, which indicated a low-frequency variation (PM2). It existedwith another pathogenic variation (PM3). SIFT, PolyPhen_2, and REVEL predicted it as harmful, harmful, and benign, respectively. According to the ACMG guidelines, the variation was preliminarily determined as being of unknown clinical significance. In case 2, there were two compound heterozygous mutations in thegene:One was c.261-2A>G, which was located in the classical splicing site (± 1, 2). It was likely to affect the normal splicing of mRNA and lead to protein truncation. The frequency in the normal population database was 0.00004, which showed that this was a low-frequency variation (PM2). According to the ACMG guidelines, this variation was preliminarily determined to be a suspected pathogenic variation (PS1). The other site was c.979G>A (p.D327N), which was a known PS1 in the Human Gene Mutation Database, and the frequency of variation in the normal population was 0.00003 (PM2).In the transposition, the suspected pathogenicity variation c.261-2A>G (PM3) was detected. SIFT, PolyPhen2, and Mutation Taster all predicted that the mutation was harmful (PP3). According to the ACMG guidelines, the variation was preliminarily determined to be a suspected PS1. According to the clinical symptoms and gene results, both children were diagnosed as having CMD caused by thegene mutation. Each child had one missense mutation, and each had a mutation leading to protein truncation. Case 1 had a frameshift mutation leading to protein truncation,whereas case 2 had a splicing mutation leading to protein truncation, suggesting that truncation mutation may be related to a severe clinical phenotype.

In this study, data from two hospitalized patients and data of 19 patients obtained from a search of the previous literature were collected, yielding data from a total of 21 patients with α-DGP caused bygene mutation. Clinical manifestations included common symptoms such as nervous system, muscular dystrophy, eye development malformation, and rare symptoms such as sensorineural deafness.Moreover, 100% of the 21 patients had nervous system involvement, and delayed cognitive and motor development. In severe cases, patients had no cognitive and motor development, and most cognitive disorders included language retardation.Patients with a mild lesion on MRI only had periventricular white matter lesions,while patients with severe lesions seen on MRI had brainstem and/or cerebellar dysplasia and neuronal migration disorders. Among the 21 patients, 63.2% had elevated creatinase that was mostly between 300 and 1740 U/L, and 26.6% of the patients had eye involvement. The common symptoms were optic nerve atrophy and eye fissure deformities (excessive small or large). Patients with extensive nervous system and muscle involvement had severe ocular symptoms such as glaucoma,cataracts, and even blindness.

明月的关系更好，而且说起来还有些复杂，边峰是自己妻子妹妹的同学。秦明月当年破获几起大案，后来都是警方的宣传人员通过边峰推向媒体的，边峰还专门写过他的专题报道，为其获评省十佳警察起了很大的作用。他知道边峰喊他是想干什么，干脆装着没听见，皱眉返回大厅，命令对寄存处的东西进行一次清查。

首次实验采用的方案是，对所有论文进行分词，去除连词、介词、代词等结构性词汇，再将其余词汇进行词频检索，按词汇出现频次高低排序，分析高频次词汇的词性规律。这是一般文本挖掘常用的方法，这样得出的高频词汇表中，很多日常用词居于排行前列，高频专业词汇数量太多且不集中，难以得出精炼的研究热点，故放弃此实验方案。

There were 12 pairs of alleles in 21 patients involving 15 Loci. Among them,c.979G>A (p.D327N) appeared three times, and c.822_823dup (pI276Lfs*26) appeared twice, suggesting that the above two sites may be focal mutations. It was further speculated that the severity of thegene mutation was still related to its mutation type and site. All four patients with biallelic truncated mutations in sporadic cases 2, 3, 7, and 19 had neuronal migration disorders (polymicrogyria or cobblestonelike surface with no gyri). Pedigree 1 and sporadic cases 8 and 21 had severe truncated mutations of a single allele (the sites were all before the 103amino acid), and they also had neuronal migration disorders or developmental brain malformations.Pedigree 3 and sporadic case 20 had mild truncated mutations of a single allele (the sites were all after the 276amino acid), and they had only white matter involvement.Other forms of mutation had relatively mild symptoms. The above results suggested that patients with a truncated mutation of the gene located more at the front of the mutation site had more severe symptoms. The missense mutation was often associated with relatively mild symptoms. Sporadic type 1 is special, in that it is a compound heterozygous missense mutation that is associated with severe symptoms such as polymicrogyria malformation and eye and muscle involvement. Further studies are required to study the mechanism underlying sporadic type 1 mutation.

CONCLUSION

This article reports two cases of CMD caused bygene mutation. Each case carried a truncated mutation and a missense mutation, while three of the four variants have not been previously reported; thus, our findings in this case report expand the gene database. Case 2 had two new phenotypes: Giant arachnoid cyst, which recovered well after surgical resection, and meningocele after birth, which gradually self-healed. These data broadened the phenotypic spectrum of the gene. Clinical characteristics of the gene mutation are summarized and analyzed through a literature search, providing clues for clinicians to diagnose and treat this gene mutation. Due to the limitation of a small number of patients, absence of functional verification, and lack of evidence at the cellular level, the clinical characteristics and pathogenic mechanisms of this mutation were not completely clarified. Further studies at a clinical level are required to support our findings.