Medical genetics, which is a frontier subject in biomedicine, is the clinical core of gene diagnosis and gene therapy. In the training of medical students, medical genetics plays an important role in bridging basic medicine and clinical medicine. In recent years, problem-based learning (PBL) has been widely used in medical education as an important method to cultivate the autonomous learning ability of medical students. In the current study, we designed and shared the research on brachydactyly type A2 (BDA2) as the main case of PBL teaching, in order to guide the students towards autonomous learning, and to cultivate independent analysis and problem solving ability instead of simple knowledge acquisition. Such excellent academic teaching will provide more high quality medical talents and internationally competitiveness for constructing a healthy China. 医学遗传学是生物医学中的前沿学科，也是临床基因诊断和基因治疗的核心内容。在医学人才培养中，医学遗传学扮演着衔接基础医学与临床医学的重要角色。近年来，基于问题的学习(problem-based learning，PBL)作为培养医学生自主学习能力的重要方法，在医学教育中得到了广泛的应用。本文设计并分享了以A2型短指(趾)症(brachydactyly type A2，BDA2)研究为核心的PBL教学案例，以期引导学生自主学习，以能力培养代替知识传授，培养学生独立分析和解决问题的能力以及创新性思维的卓越学风，为健康中国建设输送更多具有国际竞争力的高素质医学人才。.

Recently, several pedigree-based studies have shown that abnormal replication of an enhancer element regulatory region in the downstream of the bone morphogenetic protein 2 (BMP2) gene is the cause of brachydactyly type A2 (BDA2). However, the exact molecular function of this regulatory region is unclear, and even conflicting results have emerged. In this study, based on bioinformatics analysis, we amplified target fragments of different lengths in this regulatory region by PCR technology, including a highly conserved 2.1 kb core sequence and 3 fragments that can completely cover the core 2.1 kb fragment. Then, the gene recombination vectors were constructed, and the biological function of these fragments was analyzed by the dual-luciferase reporter gene technology system. We found that the highly conserved 2.1 kb fragment did not have enhancer activity, while all of three truncated fragments showed strong enhancer activity. The results suggest that the expression regulation mode of the BMP2 gene is very complex. For the downstream regulatory region, selecting fragments of different lengths may have different effects on the regulation of BMP2 expression, which may due to the fragments with different lengths carrying different regulatory elements in the number of types. In summary, this study revealed the complexity of BMP2 gene regulatory elements, and provided new clues and directions for the subsequent in-depth exploration of the molecular pathogenic mechanism of BDA2. 近年来数项基于遗传家系的研究表明，骨形态发生蛋白2(bone morphogenetic protein 2, BMP2)基因下游的远端增强子元件调控区域的异常重复是A2型短指(趾)症(brachydactyly type A2, BDA2)的致病原因，但是这段调控区域的确切分子功能尚不明确，甚至出现有相互矛盾的结果。本研究在生物信息学分析的基础上，通过PCR技术扩增了该调控区域的不同长度的目的片段，包括高度保守的2.1 kb核心序列和3个能够完全覆盖该2.1 kb片段的不同长度的截短体片段，进而构建基因重组载体，采用双荧光素酶报告基因检测方法对这些片段的生物学功能进行分析。结果发现，高度保守的2.1 kb片段并不具有增强子活性，而3个截短体片段均表现出强烈的增强子活性。这表明BMP2基因的表达调控模式非常复杂，对其下游的这段调控区域而言，选取不同长度的片段，其对BMP2表达调控的效果可能并不一致，这很可能是由于不同长度的片段所携带的调控元件数量或种类不同所致。此项研究初步揭示了BMP2基因调控元件的复杂性，为后续深入探究BDA2的分子致病机制提供了新的线索和方向。.

With the introduction of genetic tests such as chromosomal microarray analysis (CMA) and exome sequencing (ES) into fetal medical practices, genotype-phenotype correlations in intrauterine-onset disorders have substantially improved. The BMP2 gene, located on the long arm of chromosome 20 plays a role in bone and cartilage development and is associated with Brachydactyly type A2, an autosomal dominant disease characterized by malformations of the middle phalanx of the index finger and abnormalities of the second toe. However, the BMP2 gene has so far never been reported as a candidate gene for Brachydactyly type D (BDD) affecting only the thumbs. Here, we report one family possessing a maternally inherited 6.3 Mb microduplication of 20p13p12.2 including the BMP2 gene with discordant phenotypes between the mother and the fetus. The mother was affected with BDD alongside mild facial dysmorphism and learning difficulties, while the female fetus showed BDD, severe symmetric intrauterine growth restriction combined with oligohydramnios. The CMA and Trio ES tests were implemented. Trio ES ruled out other possible monogenic causes for the family. After reviewing cases and literature with duplications within this genomic region, we found that they are extremely rare and most of the cited cases were too small for comparison. The disturbance of the BMP2 gene could explain BDD, but the other clinical presentations in the mother and fetus are not yet fully understood. This study provides important evidence for the current understanding of genotype-phenotype association of this 6.3 Mb size duplication in the 20p13p12.2 region. This duplication is a unique CNV occurring so far only in this family. Further cases and research are needed to understand the discordance in the phenotypes between the mother and fetus and establish the relationship between BMP2 gene and BDD.

Brachydactylies are a group of inherited conditions, characterized mainly by the presence of shortened fingers and toes. Based on the patients' phenotypes, brachydactylies have been subdivided into 10 subtypes. In this study, we have identified a family with two members affected by brachydactyly type A2 (BDA2). BDA2 is caused by mutations in three genes: BMPR1B, BMP2 or GDF5. So far only two studies have reported the BDA2 cases caused by mutations in the BMPR1B gene. We employed next-generation sequencing to identify mutations in culpable genes. In this paper, we report a case of BDA2 resulting from the presence of a heterozygous c.1456C>T, p.Arg486Trp variant in BMPR1B, which was previously associated with BDA2. The next generation sequencing analysis of the patients' family revealed that the mutation occurred de novo in the proband and was transmitted to his 26-month-old son. Although the same variant was confirmed in both patients, their phenotypes were different with more severe manifestation of the disease in the adult.

Brachydactyly type A2 (BDA2) is an autosomal dominant disease characterized by the deformation of the middle phalanx of the second fingers and toes. It has been reported to be associated with three genes regulating the osteogenesis, including BMPR1B, GDF5 and BMP2. 10 BDA2 patients and 7 unaffected individuals in a Chinese family were identified through clinical signs and radiographs. The mutation analyses of BMPR1B, GDF5 and BMP2 gene was performed in all the available family members and 100 control subjects. The duplication analysis for the downstream of BMP2 was also performed in all the samples. A novel 4671bp duplication downstream the BMP2 gene was identified in all the patients undergoing molecular analysis but not in the unaffected individuals and healthy controls, with a 28bp microhomology flanking it. There was no mutation in all the exons of BMPR1B, GDF5 and BMP2 in all the tested family members. The novel duplication has different breakpoints compared with the previous ones but highly overlapped with them. The duplication narrows the range of the potential cis-regulatory sequence, and further supports the association between BDA2 and the duplication downstream BMP2.