ACAN基因变异致矮身材基因改变与临床观察
Gene Mutation and Its Clinical Observation of Short Stature Caused by ACAN Gene Mutation

作者: 马建英 :青岛大学附属青岛市海慈医院小儿内科,山东 青岛; 王媛媛 :潍坊市妇幼保健院儿二科,山东 潍坊; 李 堂 :青岛大学附属青岛市妇女儿童医院内分泌科,山东 青岛;

关键词: ACAN基因矮身材骨龄提前生长激素ACAN Gene Short Stature Advanced Bone Age Growth Hormone

摘要:
目的:分析ACAN基因变异与矮身材的关系,观察重组人生长激素(rhGH)的疗效与安全性。方法:回顾分析一例ACAN基因变异的矮身材患儿的临床资料,检索相关文献,总结ACAN基因变异与矮身材的关系,观察rhGH的疗效与安全性。结果:患儿为5岁7个月的女孩,矮身材,身高104.7 cm (−2.22 SD),其父亲身高175 cm (+0.42 SD),母亲身高163 cm (+0.47 SD),家族中均无矮身材者;无特殊面容及骨骼畸形,无第二性征发育;骨龄示7岁;基因测序示ACAN基因存在杂合变异c534C > G (p.N178K),其父母该位点均无变异,其为自发突变。予rhGH 50 ug∙kg−1∙d−1治疗,身高第一年增长7.8 cm (112.5 cm, −1.58 SD),后予rhGH 60 ug∙kg−1∙d−1治疗8个月,身高增长4.9 cm (117.4 cm, −1.28 SD),身高由−2.22SD追至−1.28 SD;骨龄进展2.5岁。结论:骨龄提前的矮身材患儿应考虑存在ACAN基因突变;应用rhGH治疗身高明显改善。

Abstract: Objective: To analyze the relationship between ACAN gene variation and short stature and observe the efficacy and safety of recombinant human growth hormone (rhGH). Methods: Review the clinical data of a case of idiopathic short stature with ACAN gene mutation and search the relevant literatures to summarize the relationship between ACAN gene mutation and short stature, and observe the efficacy and safety of recombinant human growth hormone. Results: The patient was a 5-year and 7 months old girl with a short stature of 104.7 cm (−2.22 SD). She had short stature and was 104.7 cm (−2.22 SD) in height. Her father was 175 cm (+0.42 SD) in height and her mother was 163 cm (+0.47 SD) in height .There was no short stature in her family. There was no special face and skeletal deformity and secondary sexual development. Her bone age was 7 years. The gene sequencing revealed a heterozygous variation (c534c > G (p.n178k)) in ACAN gene, which was spontaneous mutation. And there was no mutation in this locus of the ACAN gene in her parents. Her height increased by 7.8 cm (112.5 cm, −1.28 SD) in the first year of treatment with rhGH (50 ug∙kg−1∙d−1) and the height increased by 4.9 cm (117.4 cm, −1.28SD) after 8 months of treatment with rhGH (60 ug∙kg−1∙d−1). Her height recovered from −2.22 SD to −1.28 SD and her bone age progressed by 2.5 years. Conclusion: The ACAN gene mutation should be considered in children with advanced bone age and the height can be improved significantly by rhGH.

1. 前言

矮身材是指在相似的环境下,同种族、同性别和年龄的个体低于正常人群平均身高2个标准差(−2 SD)者或者低于第三百分位数(−1.88 SD)者 [1]。矮身材病因复杂,除下丘脑–垂体–胰岛素样生长因子-1轴的缺陷,还包括甲状腺功能减退、小于胎龄儿、染色体畸变(如Turner综合征)、骨骼发育障碍、慢性系统性疾病、营养不良、性早熟、体质性青春发育延迟等 [1]。但是约60%~80%的特发性矮身材(idiopathic short stature ISS)儿童找不到原因,多数为未知的遗传变异 [2]。目前ISS许多遗传原因被逐渐发现,如SHOX,NPR2,NPPC,FGFR3和ACAN,也使得越来越多的疾病脱离了ISS的诊断 [3]。研究表明ACAN基因变异是ISS的第二个常见的单基因原因,约占1.4% [3]。本研究回顾性分析一例确诊的ACAN基因自发突变非家族性矮小患儿的诊疗并复习相关文献,总结ACAN基因变异与矮身材的关系,观察rhGH治疗ACAN基因变异患儿的疗效与安全性。

2. 病例资料

患儿来自于山东省青岛市妇女儿童医院内分泌科。女,5岁7月,因生长缓慢就诊。患儿系G1P1,足月剖宫产分娩,无缺氧窒息史,出生时身长50 cm,体重3.25 Kg。1岁始父母发现生长速度较同龄儿童慢。该患儿自幼身体健康,无心肺及肾脏等慢性疾病;智力发育正常,性格开朗,家庭和睦;其父身高175 cm (+0.42 SD),母身高163 cm (+0.47 SD),家族中无矮身材者。查体身高104.7 cm (−2.22 SD),体重20.5 kg,双乳B1期,女性幼稚外阴,PH1期,无特殊面容及骨骼畸形。实验室检查血常规,尿常规,肝肾功能电解质,甲状腺功能,皮质醇,ACTH,17-OH孕酮,性激素及血尿串联质谱均无异常。染色体46,XX。骨龄提前,7岁。子宫卵巢彩超、下丘脑垂体核磁共振及脊柱X线未发现异常。生长激素(GH)激发试验口服可乐定GH峰值为10.26 ng/ml,静脉注射胰岛素GH峰值为8.53 ng/ml,胰岛素样生长因子-1为196.8 ug/l。经家属知情同意给予高通量全外显子基因检测,基因测序证实该患儿第15号染色体外显子处存在ACAN基因杂合变异c534C > G (p.N178K),即编码区第534号核苷酸由胞嘧啶变异为鸟嘌呤,导致第178号氨基酸由天冬酰胺变异为赖氨酸,为错义突变。根据ACMG指南,该变异初步判定为致病性变异(Likely pathogenic),经家系验证分析,受检人之父该位点无变异,受检人之母该位点无变异,此变异为自发突变(见图1)。在正常人群数据库中的频率为阴性,为低频变异。人类基因变异数据库(HGMD)未有该位点的相关性报道,该突变为国内外首次报道。生物信息学蛋白功能预测软件PolyPhen-2预测为有害。诊断为:矮身材(ACAN基因变异)。

诊断后给予长春金赛公司重组人生长激素(rhGH) 50 ug∙kg−1∙d−1皮下注射一年,身高增长7.8 cm (112.5 cm, −1.58 SD)。但后期生长速度明显减缓,于第13个月增加rhGH用量至60 ug∙kg−1∙d−1治疗8个月,身高增长4.9 cm (117.4 cm, −1.28 SD)。目前年龄7岁3个月,身高117.4 cm (−1.28 SD),体重24.8 Kg,骨龄片示9.5岁。患儿经rhGH治疗20个月,身高由−2.22 SD追至−1.28 SD (见图2),骨龄增加2.5岁(见图3)。随访中未发现第二性征发育,各项检查指标在正常范围,继续随访中。

父亲(无变异) 母亲(无变异) 患儿(杂合变异)

Figure 1. Sequencing diagrams of patient and parents

图1. 患儿及父母的测序图

注:根据2005年九省一市儿童体格发育调查数据研究制定 参考文献:中华儿科杂志,2009年7期

Figure 2. Height curve of patient

图2. 患儿身高曲线图

年龄5岁7月 骨龄7岁 年龄7岁3月骨龄9.5岁

Figure 3. X-ray of patient

图3. 患儿骨龄图片

3. 讨论

ACAN基因位于人常染色体15q26.1,由19个外显子组成,编码聚集蛋白聚糖(aggrecan) [4]。聚集蛋白聚糖是由核心蛋白(包含硫酸软骨素链和硫酸角质素链)、连接蛋白、球间结构域及G1、G2、G3三个球状结构域组成 [4]。是生长板和关节软骨细胞外基质中主要的蛋白多糖,在软骨和骨的形成中起关键作用,并吸引大量的水分子形成凝胶,赋予关节软骨承受压缩负荷的能力,维持正常的软骨关节功能 [5] [6]。ACAN基因变异可导致软骨细胞外基质的主要成分聚集蛋白聚糖缺乏,软骨细胞增殖减少,骨骼生长板功能障碍,从而导致线性生长障碍,造成身材矮小和(或)关节畸形、功能异常 [5] [6]。文献报道临床表型多样:身材矮小、早发性腰椎间盘突出症、骨软骨炎剥离和早发性骨关节炎、骨骼畸形等 [7]。到目前为止,在HGMD数据库中共收录了93种ACAN基因变异,其中错义突变62个、剪切突变3个,小缺失突变15个,插入突变3个,插入缺失突变4个,大缺失突变2个,基因重排2个。其中87.9%的突变具有遗传特征,仅有少数是散发的。该患儿突变即为散发者,为新发突变,且该突变为国内外首次报道。

既往文献报道ACAN基因变异典型的类型包括:1.常染色体显性遗传性脊柱骨骺发育不良即金伯利型(SEDK)身材矮小 [8],表现为躯干和四肢短小,并且具有早发性骨关节炎。2.常染色体隐性遗传脊柱痉挛性发育不良聚集蛋白聚糖型 [9],表现为极矮的身材(最终身高66~71厘米),颈部短,胸部、指腹、拇指宽,颅面畸形包括巨头畸形,低位旋转耳朵,并且存在严重的中面发育不全。该家系ACAN杂合变异基因携带者,表现出轻微的矮身材表型(平均成人身高在−2 SD和−4 SD之间)。3.ACAN基因杂合变异所致的特发性矮身材型(ISS) [10],表现为身材矮小,骨龄提前或有轻度的骨骼发育不良。数据显示ACAN基因变异中87.9%具有遗传特征,故其变异所致ISS类型中也以家族性矮身材最为常见。有研究认为ACAN基因变异,致软骨细胞过早肥大,诱导血管和骨细胞过早地侵入,骨细胞将新形成的软骨重塑为骨组织使骨骺过早融合,导致骨龄提前,生长过早停止 [11],所以在家族性矮身材和骨龄提前的矮身材患者中应考虑ACAN基因检测。既往文献也曾报道ACAN杂合突变在非家族性矮身材患儿中也有发现 [12],本例报道的患儿即为非家族性矮身材,其ACAN基因变异为自发突变。另外,有报道显示并不是所有的ACAN基因变异患儿都表现为骨龄提前表型,有的骨龄正常甚至轻度延迟 [12] [13]。因此,目前杂合ACAN基因突变谱逐渐扩展,不能因缺乏矮身材家族史或骨龄提前来排除该诊断。ACAN基因变异的患儿出生时身高和体重是正常的,后逐渐出现随着年龄增长的矮小,大部分患儿出现骨软骨炎剥离,早发性骨软骨炎和轻度畸形特征相关的非综合征性身材的多种表型谱,也可除矮小外没有任何其他临床异常。本研究报道的患儿除身材矮小外没有发现任何其他临床表型。目前研究发现,ACAN基因变异显示基因型与表型共分离,提示ACAN基因变异没有明显的基因型–表型相关性,表明生长板软骨形成的损害可能是由于aggrecan功能性单倍体的不足,而不是因为不同的突变机制所致 [7]。

ACAN基因变异患儿细胞外基质Aggrecan缺乏导致骨龄提前,往往在青春期早期甚至青春期前即停止生长,导致成年身高明显受损。目前缺乏相应的药物促使细胞外基质Aggrecan恢复正常,国内外文献报道对ACAN基因变异患儿矮身材的治疗,药物有rhGH、促性腺激素释放激素类似物(GnRHa)及芳香化酶抑制剂。有文献报道经rhGH治疗者至成人(n = 5)的平均身高SD评分为−2.5,未治疗者至成人(n = 65)的平均身高SD评分为−3.0,对rhGH反应有效,但与生长激素缺乏症患儿相比较差,在rhGH治疗过程中存在着随治疗时间延长身高增速减缓 [7] [14]。此外有研究表明,ACAN突变患者从青春期开始接受生长激素和促性腺激素释放激素类似物联合治疗2年,其成人身高比未治疗的相同ACAN突变的同性家庭成员高5~8 cm [15],表明联合应用GnRHa或芳香化酶抑制剂抑制骨龄进展,可使终身高获益。本研究报道的患儿经rhGH治疗20个月,身高由−2.22 SD追至−1.28 SD,与文献报道相同,其在治疗过程中对生长激素的反应也存在着随着治疗时间延长身高增速减缓。但rhGH在矮身材儿童诊治指南规定的范围内加量后生长速度短期内增加,随访过程中监测各项指标均在正常范围,近期安全性良好,其后续对rhGH的反应还需要长期随访。在随访中注意第二性征的变化,如有性腺轴启动,尽早联合GnRHa治疗。最近一项关于中国矮小儿童的研究发现ACAN基因变异在矮身材患儿中的患病率为1.2%,在骨龄提前的矮身材患儿中占14.3%,在骨龄提前和家族性矮身材患儿中占35.7% [16],但是目前对ACAN基因变异患儿的临床特点及治疗多为个案报道,没有专业的诊疗指南,所以需要更多的学者一起去探讨。

4. 结论

综上,本研究在一例骨龄提前的患儿中新发现了一种ACAN基因的自发变异,除身材矮小外,未发现骨骼畸形和特殊面容等任何其他临床表型。ACAN基因变异患儿临床表型没有特异性,并且少部分没有矮身材家族史和骨龄提前,应用rhGH治疗有效且近期安全性良好。临床工作中对骨龄提前的矮身材患儿应考虑存在ACAN基因变异,建议早期基因诊断,早期干预治疗。

文章引用: 马建英 , 王媛媛 , 李 堂 (2021) ACAN基因变异致矮身材基因改变与临床观察。 临床医学进展, 11, 1537-1543. doi: 10.12677/ACM.2021.114220

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