A mutation in the receptor binding site of GDF5 causes Mohr-Wriedt brachydactyly type A2

Background

Brachydactyly type A2 (OMIM 112600) is characterised by hypoplasia/aplasia of the second middle phalanx of the index finger and sometimes the little finger. BDA2 was first described by Mohr and Wriedt in a large Danish/Norwegian kindred and mutations in BMPR1B were recently demonstrated in two affected families.

Methods

We found and reviewed Mohr and Wriedt''s original unpublished annotations, updated the family pedigree, and examined 37 family members clinically, and radiologically by constructing the metacarpo‐phalangeal profile (MCPP) pattern in nine affected subjects. Molecular analyses included sequencing of BMPR1B, linkage analysis for STS markers flanking GDF5, sequencing of GDF5, confirmation of the mutation by a restriction enzyme assay, and localisation of the mutation inferred from the very recently reported GDF5 crystal structure, and by superimposing the GDF5 protein sequence onto the crystal structure of BMP2 bound to Bmpr1a.

Results

A short middle phalanx of the index finger was found in all affected individuals, but other fingers were occasionally involved. The fourth finger was characteristically spared. This distinguishes Mohr‐Wriedt type BDA2 from BDA2 caused by mutations in BMPR1B. An MCPP analysis most efficiently detected mutation carrier status. We identified a missense mutation, c.1322T>C, causing substitution of a leucine with a proline at amino acid residue 441 within the active signalling domain of GDF5. The mutation was predicted to reside in the binding site for BMP type 1 receptors.

Conclusion

GDF5 is a novel BDA2 causing gene. It is suggested that impaired activity of BMPR1B is the molecular mechanism responsible for the BDA2 phenotype.     

Detection of a de novo interstitial 2q microdeletion by CGH microarray analysis in a patient with limb malformations, microcephaly and mental retardation

We describe the cytogenetic diagnosis using BAC- and oligonucleotide microarrays of a 16-year-old Laotian-American female, who first presented at 2 1/2 years of age with microcephaly, developmental retardation, and skeletal abnormalities of the upper limb including mild syndactyly of the second and third and the third and fourth fingers, short middle phalanges and clinodactyly of the fifth digit at the distal interphalangel joint on both hands, and symphalangism of the metacarpal-phalangeal joints of the second and fifth digits bilaterally. Her lower limbs displayed symphalangism of the metatarsal-phalangeal joint of the second, third, and fourth digits on both feet, with fusion of the middle and distal phalanges of the second and fifth digits and hallux valgus bilaterally. G-banded chromosomal study at age 4 was normal. However, comparative genomic hybridization at age 15 with the Spectral Genomics 1 Mb Hu BAC array platform indicated a microdeletion involving two BAC clones, RP11-451F14 --> RP11-12N7 at 2q31.1. The maximal deletion on initial analysis comprised the HOXD cluster, which is implicated in limb development. Fluorescence in situ hybridization (FISH) using the RP11-451F14 probe confirmed the deletion. Both parents were negative for the deletion. Additional FISH using BAC RP11-387A1, covering the HOXD cluster, limited the maximal deletion to approximately 2.518 Mb, and excluded involvement of the HOXD cluster. The Agilent 44K and 244K platforms demonstrated a deletion of approximately 2,011,000 bp, which did not include the HOXD cluster. The malformations in our patient may be caused by deletion of a regulatory element far upstream of the HOXD cluster.     

Brachydactyly type A1 associated with unusual radiological findings and a novel Arg158Cys mutation in the Indian hedgehog (IHH) gene

Brachydactyly type A1 (BDA1; MIM 112500) is characterized by shortness or absence of the middle phalanx of the hands and feet. The condition is caused by heterozygous mutations in the Indian hedgehog (IHH) gene or a yet unidentified gene on chromosome 5p13. We investigated six affected members of a large Swedish family segregating autosomal dominant brachymesophalangia. Affected individuals show hypoplasia of the ulnar styloid processes, ulna minus, osteoarthritis, normal length of all distal phalanges and shortening or absence of the middle phalanges. Stationary ossicles or sesamoid bones were observed at the metacarpal heads in all patients. Genetic analysis of the family showed that the IHH-gene was linked to the disease (Z_max 3.42 at theta 0.00) and sequence analysis of IHH revealed a novel c.472C > T transition in all affected family members. The mutation results in a p.158Arg > Cys substitution located in the highly conserved amino-terminal domain of IHH. This domain is of importance for the interaction between IHH and the Patched receptor. Our combined findings add radiological findings to the BDA1 phenotype and confirm a critical functional domain of IHH.     

A novel microdeletion upstream of HOXD13 in a Chinese family with synpolydactyly

Synpolydactyly (SPD) is a digital malformation with the typical clinical phenotype of the webbing of 3/4 fingers and/or 4/5 toes, and combined with polydactyly. In this study, we investigated a Chinese family with SPD and genetic analysis found that all of the affected individuals in the family carry a heterozygous 11,451 bp microdeletion at chr2:176933872-176945322 (GRCh37), which is located upstream of HOXD13 gene, the known disease gene for SPD1. All the affected individuals in the family carry the heterozygous deletion variant, and the variant co-segregated with SPD in the family. Thus, we speculate that the 11,451 bp microdeletion is the disease-causing variant in the family. To date, the microdeletion associating with SPD1 which we identified is the smallest deletion upstream of the HOXD13 gene and not altering the sequence of the HOXD13 gene.     

中国人并多指(趾)畸形家系中HOXD13基因突变及产前诊断

目的对中国山东一个并多指(趾)，又称Ⅱ型并指(趾)，畸形大家系进行致病基因突变的鉴定．确定中国人并多指(趾)畸形家系中是否存在HOXD13基因突变；通过检测突变HOXD13基因对高危胎儿进行产前基因诊断。方法根据家族史、临床体征和手足X线检查进行临床诊断；采集家系成员外周血标本及受检孕妇羊水和绒毛标本，常规提取基因组DNA；设计并合成1对特异引物，通过PCR扩增HOXD13基因第1外显子内多聚丙氨酸链编码序列；PCR扩增片段经琼脂糖凝胶电泳检测，异常扩增片段经TA克隆后测序鉴定；产前诊断中，通过PCR扩增、变性聚丙烯酰胺凝胶电泳和银染检查HOXD13基因内及基因两侧共3个微卫星多态标记进行单体型分析。结果本家系4代54人，患者16人(男6人，女10人)；手足共同表现为：3／4完全并指伴软组织蹼内多指，4／5并趾伴软组织蹼内多趾．外显率为100％，表现度变异明显。上述表现符合典型常染色体显性并多指(趾)的表型特征。对家系中18人(患者9人)进行HOXD13基因分析，结果显示：全部患者多聚丙氨酸链中丙氨酸残基数由正常的15个延长为24个。通过HOXD13基因多聚丙氨酸链延展突变检测和单体型分析，对家系中1女性患者两次怀孕进行产前诊断，发现胎儿均携带突变HOXD13基因。结论首次在中国人典型并多指(趾)大家系中发现HOXD13基因多聚丙氨酸链延展突变；联合HOXD13基因多聚丙氨酸链延展突变检测和单体型分析，首次完成2例并多指(趾)胎儿的产前基因诊断。     

Clinical phenotype associated with homozygosity for a HOXD13 7-residue polyalanine tract expansion

Synpolydactyly (SPD) is an autosomal dominant malformation of the distal limbs caused by mutations in the homeobox gene HOXD13 located on chromosome 2q31. We detail the clinical findings in a consanguineous Pakistani family segregating a HOXD13 7-residue polyalanine tract expansion. Three members of this pedigree were heterozygotes with features typical of SPD. Two further members demonstrate a more severe phenotype consistent with homozygosity for the familial mutation. We also report a child from a consanguineous Somali family homozygous for the same molecular lesion. Characteristic changes include a complex central polydactyly in the hands, abnormal modelling of the metacarpals and metatarsals, an increased number of carpal bones with abnormal shapes, hypoplasia or absence of the fifth digital rays in the feet, hypoplasia of the middle phalanges and abnormally long proximal phalanges in hands and feet. These cases illustrate the distinct phenotype associated with homozygosity for a HOXD13 mutation and also highlight the importance of considering homozygosity for a dominant mutation in consanguineous pedigrees.     

A 72-year-old Danish puzzle resolved--comparative analysis of phenotypes in families with different-sized HOXD13 polyalanine expansions

A phenotype-genotype correlation was previously described for carriers of different sized of polyalanine expansions in HOXD13. We report on a detailed comparison of 55 members (approximately 220 limbs) from 4 Danish families with duplications of 21 or 27 bp, expanding the polyalanine repeat from 15 to 22 and 24 residues, respectively. Two of these were previously described by Danish pioneers of human genetics, Tage Kemp and Oluf Thomsen. A clinical score was assigned to each limb based on manifestations assumed to represent different degrees of a duplication defect in hand rays 3-4 and foot rays 4-5. The length of metacarpals and phalangeal bones in rays 1, 2, and 5 was measured on hand radiographs and converted to Z-scores. The relative difference between corresponding right and left bones and directional, total, and fluctuating asymmetry was calculated for each individual. All of these parameters were compared between carriers of the +9 alanine expansion, the +7 alanine expansion, and non-mutation carriers with affected parents from the two families. Upper limb scores and the rate of abnormal bones (>2SD) were significantly higher in the first group than in the others. The first metacarpal and the middle phalanx of the little finger were significantly shorter, and the proximal phalanx of the index finger was significantly longer in this group than in the others. An increased level of total and fluctuating asymmetry was observed in long expansion carriers. Thus, our data have added evidence to the phenotype-genotype correlation previously reported, which was further extended to include lesser involvement of bones in ray 1, 2, and 5.     

HOXD13-associated synpolydactyly: Extending and validating the genotypic and phenotypic spectrum with 38 new and 49 published families

PurposeHOXD13 is an important regulator of limb development. Pathogenic variants in HOXD13 cause synpolydactyly type 1 (SPD1). How different types and positions of HOXD13 variants contribute to genotype-phenotype correlations, penetrance, and expressivity of SPD1 remains elusive. Here, we present a novel cohort and a literature review to elucidate HOXD13 phenotype-genotype correlations.MethodsPatients with limb anomalies suggestive of SPD1 were selected for analysis of HOXD13 by Sanger sequencing, repeat length analysis, and next-generation sequencing. Literature was reviewed for HOXD13 heterozygotes. Variants were annotated for phenotypic data. Severity was calculated, and cluster and decision-tree analyses were performed.ResultsWe identified 98 affected members of 38 families featuring 11 different (likely) causative variants and 4 variants of uncertain significance. The most frequent (25/38) were alanine repeat expansions. Phenotypes ranged from unaffected heterozygotes to severe osseous synpolydactyly, with intra- and inter-familial heterogeneity and asymmetry. A literature review provided 160 evaluable affected members of 49 families with SPD1. Computer-aided analysis only corroborated a positive correlation between alanine repeat length and phenotype severity.ConclusionOur findings support that HOXD13-protein condensation in addition to haploinsufficiency is the molecular pathomechanism of SPD1. Our data may, also, facilitate the interpretation of synpolydactyly radiographs by future automated tools.     

TGDS pathogenic variants cause Catel‐Manzke syndrome without hyperphalangy

Catel‐Manzke syndrome, also known as micrognathia‐digital‐syndrome, is a rare autosomal recessive disorder characterized by the combination of the two cardinal features Pierre‐Robin sequence and bilateral hyperphalangy leading to ulnar clinodactyly (ulnar curvature of the phalanges) and radial deviation (radial angulation at the metacarpophalangeal joint) of the index fingers. Individuals without one of these major hallmarks or with additional hand malformations have been described as atypical or Catel‐Manzke‐like syndrome. Biallelic TGDS pathogenic variants have thus far been detected in eight individuals with typical Catel‐Manzke syndrome and in one fetus with additional features. Here we report on two individuals with TGDS pathogenic variants who presented with mild radial deviation and ulnar clinodactyly of the index fingers but without radiologic signs of hyperphalangy. Furthermore, both individuals have disproportionate short stature, a feature that has not yet been associated with Catel‐Manzke syndrome. Our data broaden the phenotypic spectrum of TGDS‐associated Catel‐Manzke syndrome and expand the indication for diagnostic testing.     

Two novel disease-causing variants in BMPR1B are associated with brachydactyly type A1

Brachydactyly type A1 is an autosomal dominant disorder primarily characterized by hypoplasia/aplasia of the middle phalanges of digits 2–5. Human and mouse genetic perturbations in the BMP-SMAD signaling pathway have been associated with many brachymesophalangies, including BDA1, as causative mutations in IHH and GDF5 have been previously identified. GDF5 interacts directly as the preferred ligand for the BMP type-1 receptor BMPR1B and is important for both chondrogenesis and digit formation. We report pathogenic variants in BMPR1B that are associated with complex BDA1. A c.975A>C (p.(Lys325Asn)) was identified in the first patient displaying absent middle phalanges and shortened distal phalanges of the toes in addition to the significant shortening of middle phalanges in digits 2, 3 and 5 of the hands. The second patient displayed a combination of brachydactyly and arachnodactyly. The sequencing of BMPR1B in this individual revealed a novel c.447-1G>A at a canonical acceptor splice site of exon 8, which is predicted to create a novel acceptor site, thus leading to a translational reading frameshift. Both mutations are most likely to act in a dominant-negative manner, similar to the effects observed in BMPR1B mutations that cause BDA2. These findings demonstrate that BMPR1B is another gene involved with the pathogenesis of BDA1 and illustrates the continuum of phenotypes between BDA1 and BDA2.     

Clinical and molecular analysis of Grebe acromesomelic dysplasia in an Omani family

Grebe syndrome is a rare autosomal recessive acromesomelic dysplasia. The syndrome was studied clinically, radiographically, and genetically in an Omani family with four affected children. The affected persons had normal axial skeletons, severely shortened, and deformed limbs with severity increasing in a proximo-distal gradient, and subluxated joints. The humeri and femora were hypoplastic with distal malformations. The radii/ulnae were shortened and deformed whereas carpal bones were invariably rudimentary or absent. The tibiae appeared rudimentary; fibulae were absent in two children, and some tarsal and metatarsal bones were absent. The proximal and middle phalanges were absent while the distal phalanges were present. The father and mother had short first metacarpal and middle phalynx of the fifth finger and hallux valgus respectively. Transition A1137G and deletion delG1144 mutations in the gene encoding the cartilage-derived morphogenetic protein-1 (CDMP-1) were identified in this family. The A1137G is a silent mutation coding for lysine, whereas the delG1144 predicts a frameshift mutation resulting in a presumable loss of the CDMP-1 biologically active carboxy-terminal domain. The affected siblings were homozygous for the delG1144 mutation while parents were heterozygous.     

Mutations in GDF5 presenting as semidominant brachydactyly A1

Brachydactyly A1 (BDA1) is an autosomal dominant disorder characterized by shortness of all middle phalanges of the hands and toes, shortness of the proximal phalanges of the first digit, and short stature. Missense mutations in the Indian Hedgehog gene (IHH) are known to cause BDA1, and a second locus has been mapped to chromosome 5p. In a consanguineous French Canadian kindred with BDA1, both IHH and the 5p locus were excluded. Microsatellites flanking GDF5 on chromosome 20q were found to cosegregate with the disease. Sequencing of the GDF5 coding region revealed that a mildly affected individual in the family was heterozygous, and that all of the severely affected individuals were homozygous for a novel missense c.1195C>T mutation that predicts a p.Arg399Cys substitution at a highly conserved amino acid. Functional analysis demonstrated that although the p.Arg399Cys mutant is able to stimulate chondrogenesis, it is much less effective than wild‐type GDF5. This data confirms genetic heterogeneity in BDA1, demonstrates that mutations upstream of IHH can result in BDA1, and shows that BDA1 can result from semidominant mutations in GDF5. Hum Mutat 31:1–8, 2010. © 2010 Wiley‐Liss, Inc.     

Scope of Alagille syndrome

We report clinical and cytogenetic findings of 4 children (2 boys and 2 girls) with the Smith–Magenis syndrome. All 4 patients had an interstitial deletion of 17p: del(17) (p11.2p11.2). Their clinical manifestations included brachycephaly, midface hypoplasia, prognathism, upper lip eversion, short and broad hands with short fingers, clinodactyly of the fifth fingers, fingertip pads, moderate mental retardation, and behavior problems. Analysis of the metacarpophalangeal pattern profiles in patient 2 showed progressive shortness from the metacarpals to the proximal, middle, and the distal phalanges. The finger-pads observed in all 4 patients have hitherto been noted in only one of 26 previously reported patients with the syndrome. These findings serve as a useful clue to the diagnosis of the syndrome.     

A novel microdeletion at chromosome 2q31.1-31.2 in a three-generation family presenting duplication of great toes with clinodactyly

HOXD gene cluster maps to chromosome 2q31 and plays a key role in embryonic limb morphogenesis. Mutations of the HOXD13 and HOXD10 genes have been found to be associated with digital and limb malformations. In addition, dysregulation of HOXD gene cluster has been proposed to account for the limb abnormalities in patients with chromosome 2q rearrangements. In this report, we investigated a three-generation family presenting clinical phenotypes of duplication of great toes, tapering fingers, and clinodactyly of the fifth finger in both hands, which were transmitted in a dominant fashion in this family. We identified and validated an interstitial microdeletion of ∼3.4 Mb at chromosome 2q31.1-31.2 by array-based comparative genomic hybridization, fluorescence in situ hybridization, and real-time quantitative polymerase chain reaction that cosegregates with the clinical phenotypes in this family. The microdeletion removes 30 labeled genes including the entire HOXD gene cluster, suggesting that the digital abnormalities of this family may be attributed to the haploinsufficiency of the HOXD gene cluster. The delineation of the microdeletion region may contribute to the genotype–phenotype correlation study in patients with genomic rearrangements of the long arm of chromosome 2 and helps to understand the pathogenesis of haploinsufficiency of the HOXD gene cluster.     

Mesoaxial complete syndactyly and synostosis with hypoplastic thumbs: an unusual combination or homozygous expression of syndactyly type I?

Syndactyly type I is an autosomal dominant condition with complete or partial webbing between the third and fourth fingers or the second and third toes or both. We report here a previously undescribed phenotype of severe mesoaxial syndactyly and synostosis in patients born to affected parents. The characteristic features of these severe cases are (1) complete syndactyly and synostosis of the third and fourth fingers; (2) severe bone reduction in the proximal phalanges of the same fingers; (3) hypoplasia of the thumbs and halluces; (4) aplasia/hypoplasia of the middle phalanges of the second and fifth fingers; and (5) complete or partial soft tissue syndactyly of the toes. We report on three offspring with this phenotype from two different branches of a syndactyly type I family, suggesting that they may be homozygous for this condition. SSCP and linkage analysis indicated that neither HOXD13 nor other relevant genes in the chromosome 2q31 region was responsible for this phenotype.     

A 1型短指/趾症的临床实践指南

A1型短指/趾症(bmchydactyly type A1)是首例被记载的常染色体显性遗传病,患者以中节指/趾骨变短、并可能与远节指/趾骨融合为主要特征,迄今为止全球已发现100多个家系。本文对A1型短指/趾症的临床表现、发病机制、诊断标准、治疗方案等进行了总结,旨在提高中国医务工作者对该病的诊断水平,并对患者的临床管理提供建议。     

Arachnodactyly and unusual dermatoglyphics: study of a case

Clinical and dermatoglyphic findings are reported on a 3-yr old girl with multiple congenital anomalies and unusual dermatoglyphics. The anomalies, including contractural arachnodactyly, rhizomelia (a relative shortening of the proximal segment of the limbs), skin dimples, clinodactyly, disharmonic hand bone maturation, absent, hypoplastic and unusually positioned digital and metacarpophalangeal flexion creases, are not indicative of Marfan syndrome, but it is unclear what this syndrome constitutes. Among the child's most striking dermatoglyphic features, the fingertip patterns (mostly large whorls with extralimital triradii) extend proximally to the middle phalanx and are associated with unusually placed triradii. The furrows between the epidermal ridges are narrower on the volar aspects of the middle and distal phalanges than on the proximal phalanges and palms, resulting in a higher ridge density in the former areas. Dermatoglyphic comparisons between the proposita and her parents are provided. These dermatoglyphic aberrations may indicate the presence of a deleterious agent active during the period of the development of the ridge configurations and of the digital flexion creases.     

A new spontaneous mouse mutation of Hoxd13 with a polyalanine expansion and phenotype similar to human synpolydactyly

Human synpolydactyly (SPD) is an inherited congenital limb malformation caused by mutations in the HOXD13 gene. Heterozygotes are typically characterized by 3/4 finger and 4/5 toe syndactyly with associated duplicated digits; hands and feet of homozygotes are very small because of a shortening of the phalanges, metacarpal and metatarsal bones. Here we describe the phenotype and molecular basis of a spontaneous mutation of Hoxd13 in mice that provides a phenotypically and molecularly accurate model for human SPD. The new mutation, named synpolydactyly homolog (spdh), is a 21 bp in-frame duplication within a polyalanine- encoding region at the 5'-end of the Hoxd13 coding sequence. The duplication expands the stretch of alanines from 15 to 22; the same type of expansion occurs in human SPD mutations. spdh/spdh homozygotes exhibit severe malformations of all four feet, including polydactyly, syndactyly and brachydactylia. The phenotype of spdh is much more severe than that exhibited by mice with a genetically engineered, presumably null, disruption of Hoxd13. Thus spdh probably acts in a dominant-negative manner and will be valuable for examining interactions with other Hox genes and their protein products during limb development. Homozygous mice of both sexes also lack preputial glands and males do not breed; therefore, spdh/spdh mice may also be valuable in studies of reproductive physiology and behavior.      

一个并指(趾)多指(趾)家系的 HOXD13基因突变研究

目的 研究一个中国人并指(趾)多指(趾)(synpolydactyly，SPD)家系的临床特征，检测患者中是否存在同源盒D13基因(homeobox D13，HOXD13）突变。方法 现场调查获取临床资料和19个家系成员的外周血液标本；PCR扩增HOXD13基因突变热点序列进行突变检测；并扩增全编码区用于检测是否存在其他位点的突变；采用2％琼脂糖凝胶电泳初步分析PCR产物，5％聚丙烯酰胺凝胶电泳分离突变片段，纯化后将所有产物直接测序进行基因检测。结果 患者HOXD13基因第1外显子额外插入了编码8个丙氨酸残基的序列，可认为是正常基因中编码第5～12丙氨酸残基序列的异常重复。结论 证实该家族畸形可由HOXD13基因的多聚丙氨酸链扩展突变引起。     

一个中国人并多指(趾)畸形家系中HOXD13基因突变的检测

目的 在一个中国汉族并多指(趾)畸形家系中检测HOXD13基因致病突变.方法 通过PCR扩增HOXD13基因外显子序列,对产物进行直接测序及TA克隆测序寻找致病突变.结果 在患者中发现HOXD13基因外显子1的5'末端丙氨酸重复区内,具有27bp的不完全三核苷酸重复的插入突变,使其多聚丙氨酸链延长了9个丙氨酸残基.结论 HOXD13基因内9个丙氨酸残基的延展突变为该家系的致病突变.