软骨发育不全患儿1例的临床特点和分子机制分析

Study on clinical characteristics and molecular mechanisms of an achondroplasia child

目的分析软骨发育不全(achondroplasia,ACH)患儿的临床特点及其分子生物学机制。方法收集1名4岁ACH患儿的临床资料、实验室检查结果和影像学资料,并通过运动试验、左旋多巴兴奋试验、精氨酸刺激试验和胰岛素低血糖兴奋试验评价患儿生长激素(growth hormone,GH)水平。另外提取患儿及其父母、7名健康成人的外周血基因组DNA,PCR扩增成纤维细胞生长因子受体3(firbroblast growth factor receptor 3,FGFR3)基因第10外显子,并对扩增产物进行DNA测序。结果该名患儿具有ACH典型的临床表现,如头大,前额突出,方颅;不成比例性身材矮小,躯干正常,四肢短粗;手指粗短,三叉手等。运动试验显示GH峰值4.8 ng/ml;左旋多巴兴奋试验GH峰值42.38 ng/ml;精氨酸刺激试验GH峰值7.31 ng/ml;胰岛素低血糖兴奋试验显示:低血糖出现时(血糖2.6 mmol/L),GH显著升高至23.29 ng/ml,同时血皮质醇和ACTH水平也显著升高。给予ACH患儿重组人类生长激素(rhGH)2.5 IU/d治疗6个月,患儿身高有所改善。DNA测序显示ACH患儿FGFR3基因第10外显子的1138位核苷酸发生了G到A的转换(G1138A),该突变为错义突变,使得其所编码的FGFR3蛋白的第380位氨基酸由甘氨酸变为精氨酸(G380R),患儿父母及7名健康对照者FGFR3基因第10外显子均未发现突变。结论FGFR3基因G1138A杂合突变为该ACH患儿发病的主要原因。对于ACH患者,GH治疗有可能起到一定的作用,但远期作用仍需长期观察。

Objective To investigate the clinical characteristics and molecular mechanism of a child clinically diagnosed with achondroplasia（ACH）.Methods The clinical data,laboratory test results and imaging features were collected.The growth hormone （GH） levels of the child with ACH were evaluated through the exercise test,L-dopa stimulation test,arginine stimulation test,and insulin hypoglycemia stimulation test.Genomic DNAs from the child with ACH,his parent and 7 healthy controls were prepared for PCR.A set of primers were designed to amplify exon 10 that encodes the the firbroblast growth factor receptor 3 （FGFR3） protein and the adjacent intron region.Products of PCR were purified and sequenced directly.Results The child had typical clinical manifestations of ACH,such as large head,a prominent forehead,short upper arms and legs,and short hands with fingers that assume a trident.The peak GH concentration was 4.8 ng/ml by exercise test,42.38 ng/ml by L-dopa stimulation test,7.31 ng/ml by arginine stimulation test,and 23.29 ng/ml by insulin hypoglycemia stimulation test.After the child was given recombinant human growth hormone （rhGH） 2.5 IU/d for 6 months,the height of the child was significantly improved.A de novo heterozygous G1138A mutation was detected in the child with ACH,and this mutation made the amino acid at position 380 of the FGFR3 protein change from glycine to arginine.No any mutation in exon 10 of FGFR3 gene was found in the parent and normal controls.Conclusion The G-A transition mutation at nucleotide 1138 may be the pathologic cause of this child with ACH.For ACH patients,GH treatment is still possible to achieve a certain effect.