HOXD13 polyalanine tract expansion in classical synpolydactyly type Vordingborg

In 1927, Oluf Thomsen, in a classic paper, described a seven-generation family with autosomal dominant axial synpolydactyly (SPD)--the Vordingborgtyp of axis duplication and dysostosis. Expansion of a polyalanine tract in the HOXD13 gene is known to cause synpolydactyly. We have rediscovered part of the family described by Thomsen, and detected a 9 triplet polyalanine expansion within HOXD13segregating with the disorder. The phenotypic spectrum in mutation carriers ranged from severe to inapparent bone malformations. In the latter case, only dermatoglyphics revealed the genetic status.     

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。     

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。     

A nonsense mutation in the HOXD13 gene underlies synpolydactyly with incomplete penetrance

Synpolydactyly 1 (SPD1; OMIM 186000), also known as type II syndactyly, is a dominantly inherited limb malformation that is characterized by an increased number of digits. SPD1 is most commonly caused by polyalanine repeat expansions in the coding region of the HOXD13 gene, which are believed to show a dominant-negative effect. In addition, missense and out-of-frame deletion mutations in the HOXD13 gene are also known to cause SPD, and the mechanism responsible for the phenotype appears to be haploinsufficiency. Here, we analyzed a large consanguineous family from Pakistan with SPD showing a wide variation in phenotype among affected individuals. We performed genetic linkage analysis, which identified a region on chromosome 2 containing the HOXD13 gene. Haplotype analysis with microsatellite markers suggested segregation of the phenotype with HOXD13 gene with incomplete penetrance. Direct sequencing analysis of HOXD13 gene revealed a nonsense mutation, designated as Q248X. All affected individuals with the severe SPD phenotype are homozygous for the mutation, whereas those with the mild SPD phenotype are heterozygous for the mutation. Furthermore, some unaffected individuals also carry the mutation in the heterozygous state, showing incomplete penetrance. Our results show the first nonsense mutation in the HOXD13 gene underlying a severe form of SPD in the homozygous state, and a milder form of SPD with ～50% penetrance in the heterozygous state, most likely because of the production of 50% of protein compared with normal individuals.     

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.     

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.     

Polyalanine repeat expansion mutation of the HOXD13 gene in a Chinese family with unusual clinical manifestations of synpolydactyly

Synpolydactyly (SPD) is an autosomal dominant limb malformation caused by mutations in the gene HOXD13. We investigated a Chinese family in which three individuals across three generations were affected with distinctive limb malformations. We extracted genomic DNA from the affected and three unaffected individuals from this family as well as 100 unrelated controls, for mutation detection by DNA sequencing. The family was characterized by camptodactyly and symphalangism of fingers two to five, transverse phalanx and osseous fusion of the third metacarpal with the proximal phalanx, as well as the coexistence of mild and more severe bilateral phenotypes. We identified a duplication mutation, c. 186-212dup, in exon 1 of the HOXD13 gene in the affected individuals from this family; it was not present in the unaffected individuals or the 100 unrelated individuals. And we also did not find polymorphism among the controls. This study has expanded the phenotypic spectrum of known HOXD13 polyalanine repeat mutations and provided more information about the polymorphic nature of the polyalanine repeat. In addition, new clinical manifestations have been added to the spectrum of possible synpolydactyly phenotypes.     

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.     

An N-terminal G11A mutation in HOXD13 causes synpolydactyly and interferes with Gli3R function during limb pre-patterning

Synpolydactyly (SPD) is a distal limb anomaly characterized by incomplete digit separation and the presence of supernumerary digits in the syndactylous web. This phenotype has been associated with mutations in the homeodomain or polyalanine tract of the HOXD13 gene. We identified a novel mutation (G11A) in HOXD13 that is located outside the previously known domains and affects the intracellular half life of the protein. Misexpression of HOXD13(G11A) in the developing chick limb phenocopied the human SPD phenotype. Finally, we demonstrated through in vitro studies that this mutation has a destabilizing effect on GLI3R uncovering an unappreciated mechanism by which HOXD13 determines the patterning of the limb.     

Synpolydactyly and HOXD13 polyalanine repeat: addition of 2 alanine residues is without clinical consequences

Background  

Type II syndactyly or synpolydactyly (SPD) is clinically very heterogeneous, and genetically three distinct SPD conditions are known and have been designated as SPD1, SPD2 and SPD3, respectively. SPD1 type is associated with expansion mutations in HOXD13, resulting in an addition of ≥ 7 alanine residues to the polyalanine repeat. It has been suggested that expansions ≤ 6 alanine residues go without medical attention, as no such expansion has ever been reported with the SPD1 phenotype.     

New type of synpolydactyly of hands and feet in two unrelated males

An 18-year-old Japanese boy and a 10-year-old Chinese boy both had nearly complete cutaneous syndactyly of the fingers and toes, six diphalangeal fingers on each hand, six toes on each foot (except the right foot of patient 2), and short, deformed, and on occasion partially fused metacarpals and metatarsals. Neither had other malformations and were of normal intelligence. The accessory toes in patient 1 were mesoaxial, each situated between the hallux and the third toe, whereas those in patient 2 were postaxial. In view of these findings, the disorder in 2 individuals is likely to represent a hitherto undescribed type of nonsyndromic synpolydactyly.     

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.      

Genomic structure of Candida stellatoidea: extra chromosomes and gene duplication.

Candida albicans and Candida stellatoidea are two closely related imperfect yeasts. Some isolates characterized as C. stellatoidea are in fact C. albicans, while others differ with respect to virulence and to karyotype, containing extra small chromosomes. Experiments in this study allowed us to infer that a typical C. stellatoidea isolate, Y2360, has 12 chromosomes rather than the 7 previously shown for C. albicans. The majority of cloned sequences tested hybridized to analogous chromosomes in C. albicans and in C. stellatoidea, although there were exceptions, and a repeated element isolated as specific for C. albicans hybridized to most of the chromosomes of C. stellatoidea. Several genes tested hybridized to one of the smaller, C. stellatoidea-specific chromosomes as well as to a larger one. The arrangement of restriction enzyme sites around the gene was the same in both the large and small chromosomes. For ADE2 and LYS2, the arrangements were identical to those of a typical C. albicans strain, FC18, suggesting a high degree of sequence conservation between the two species. Spheroplast fusion and segregation experiments showed that the ADE2 genes on both the large and small chromosomes of C. stellatoidea are active, implying that the organism is functionally at least triploid for this gene and probably for any others duplicated on the smaller chromosomes.     

Type II familial synpolydactyly: report on two families with an emphasis on variations of expression

Type II familial synpolydactyly is rare and is known to have variable expression. However, no previous papers have attempted to review these variations. The aim of this paper was to review these variations and show several of these variable expressions in two families. The classic features of type II familial synpolydactyly are bilateral synpolydactyly of the third web spaces of the hands and bilateral synpolydactyly of the fourth web spaces of the feet. Several members of the two families reported in this paper showed the following variations: the third web spaces of the hands showing syndactyly without the polydactyly, normal feet, concurrent polydactyly of the little finger, concurrent clinodactyly of the little finger and the ‘homozygous'' phenotype. It was concluded that variable expressions of type II familial synpolydactyly are common and awareness of such variations is important to clinicians.     

Grebe-Quelce-Salgado chondrodystrophy: prenatal diagnosis of two new cases in unrelated families in Southern Brazil

Grebe-Quelce-Salgado chondrodystrophy is an autosomal recessive non-lethal skeletal dysplasia. Affected individuals have normal head, neck, and trunk skeleton, relatively normal humeri and femora, short and deformed radii, ulnae, tibiae, and fibulae, and severe abnormalities of hands and feet. Polydactyly is frequent. Digits present as globular appendages and are characteristic of the condition. The disease is caused by a missense mutation in the gene encoding cartilage-derived morphogenetic protein-1 (CDMP-1). Most cases described in the literature are from Brazil and, among these, all had ancestors from a particular region in the state of Bahia. We describe two cases of Grebe-Quelce-Salgado chondrodystrophy visualized by prenatal ultrasound. The patients presented in this report do not descend from the population of Bahia and, to our knowledge, case two is the only case with prenatal clinical diagnosis in a family with no previously affected children.