Institute for Medical Genetics and Human Genetics, Charité-Universitätsmedizin Berlin, Berlin, Germany.
J Med Genet. 2012 Feb;49(2):119-25. doi: 10.1136/jmedgenet-2011-100409. Epub 2011 Dec 6.
Split-hand/foot malformation (SHFM)-also known as ectrodactyly-is a congenital disorder characterised by severe malformations of the distal limbs affecting the central rays of hands and/or feet. A distinct entity termed SHFLD presents with SHFM and long bone deficiency. Mouse models suggest that a defect of the central apical ectodermal ridge leads to the phenotype. Although six different loci/mutations (SHFM1-6) have been associated with SHFM, the underlying cause in a large number of cases is still unresolved.
High resolution array comparative genomic hybridisation (CGH) was performed in patients with SHFLD to detect copy number changes. Candidate genes were further evaluated for expression and function during limb development by whole mount in situ hybridisation and morpholino knock-down experiments.
Array CGH showed microduplications on chromosome 17p13.3, a locus previously associated with SHFLD. Detailed analysis of 17 families revealed that this copy number variation serves as a susceptibility factor for a highly variable phenotype with reduced penetrance, particularly in females. Compared to other known causes for SHFLD 17p duplications appear to be the most frequent cause of SHFLD. A ~11.8 kb minimal critical region was identified encompassing a single gene, BHLHA9, a putative basic loop helix transcription factor. Whole mount in situ hybridisation showed expression restricted to the limb bud mesenchyme underlying the apical ectodermal ridge in mouse and zebrafish embryos. Knock down of bhlha9 in zebrafish resulted in shortening of the pectoral fins.
Genomic duplications encompassing BHLHA9 are associated with SHFLD and non-Mendelian inheritance characterised by a high degree of non-penetrance with sex bias. Knock-down of bhlha9 in zebrafish causes severe reduction defects of the pectoral fin, indicating a role for this gene in limb development.
分裂手/足畸形（SHFM）-也称为并指畸形-是一种先天疾病，其特征是远端肢体严重畸形，影响手和/或脚的中央射线。一个称为 SHFLD 的独特实体表现为 SHFM 和长骨缺失。小鼠模型表明中央顶外胚层嵴的缺陷导致表型。尽管已经与 SHFM 相关的六个不同基因座/突变（SHFM1-6），但在大量病例中，其根本原因仍未解决。
对 SHFLD 患者进行高分辨率微阵列比较基因组杂交（CGH），以检测拷贝数变化。通过整体原位杂交和形态发生素敲低实验，进一步评估候选基因在肢体发育过程中的表达和功能。
CGH 显示染色体 17p13.3 上存在微重复，该基因座先前与 SHFLD 相关。对 17 个家庭的详细分析表明，这种拷贝数变异作为一种易感性因素，导致具有低外显率的高度可变表型，特别是在女性中。与其他已知的 SHFLD 原因相比，17p 重复似乎是 SHFLD 的最常见原因。确定了一个包含单个基因 BHLHA9 的~11.8 kb 最小关键区域，该基因是一种假定的基本环螺旋转录因子。在小鼠和斑马鱼胚胎中，整体原位杂交显示其在肢芽间充质中的表达仅限于顶外胚层嵴下。在斑马鱼中敲低 bhlha9 导致胸鳍缩短。
包含 BHLHA9 的基因组重复与 SHFLD 相关，非孟德尔遗传特征为非外显率高，具有性别偏倚。在斑马鱼中敲低 bhlha9 会导致胸鳍严重减少缺陷，表明该基因在肢体发育中起作用。
