A new locus for postaxial polydactyly type A/B on chromosome 7q21-q34

Polydactyly: Clinical and molecular manifestations

Polydactyly is a malformation during the development of the human limb, which is characterized by the presence of more than the normal number of fingers or toes. It is considered to be one of the most common inherited hand disorders. It can be divided into two major groups: Non-syndromic polydactyly or syndromic polydactyly. According to the anatomical location of the duplicated digits, polydactyly can be generally subdivided into pre-, post-axial, and mesoaxial forms. Non-syndromic polydactyly is often inherited with an autosomal dominant trait and defects during the procedure of anterior-posterior patterning of limb development are incriminated for the final phenotype of the malformation. There are several forms of polydactyly, including hand and foot extra digit manifestations. The deformity affects upper limbs with a higher frequency than the lower, and the left foot is more often involved than the right. The treatment is always surgical. Since the clinical presentation is highly diverse, the treatment combines single or multiple surgical operations, depending on the type of polydactyly. The research attention that congenital limb deformities have recently attracted has resulted in broadening the list of isolated gene mutations associated with the disorders. Next generation sequencing technologies have contributed to the correlation of phenotype and genetic profile of the multiple polydactyly manifestations and have helped in early diagnosis and screening of most non-syndromic and syndromic disorders.

Genetic overview of postaxial polydactyly: Updated classification

Polydactyly or polydactylism, also known as a hyperdactyly, is a congenital limb defect with various morphologic phenotypes. Apart from physical and functional impairments, the presence of polydactyly is an indication of an underlying syndrome in the newborn. Usually, it follows as an autosomal dominant/recessive inheritance pattern with defects in the limb development's anteroposterior patterning. Although mutations in several genes have been associated with polydactyly; however, the exact underlying cause, pathways, and disease mechanisms are still unexplored, thus making it of multi-factorial origin. Polydactyly is divided into three subtypes; radial, ulnar, and central polydactyly. So far, 11 loci (PAPA1-PAPA11) and seven human genes have been reported to cause non-syndromic postaxial polydactyly in humans, including the ZNF141, GLI3, IQCE, GLI1, FAM92A1, KIAA0825, and DACH1. In this review, we discuss emerging evidences of clinical and molecular characterization of polydactyly types in term of the involvement of newly associated genes and loci for non-syndromic postaxial polydactyly, and how these might impact our understanding of the genetic mechanisms and molecular etiology involved in the cause of polydactyly.

A review of polydactyly and its inheritance: Connecting the dots

OBJECTIVE

This study collects what is known about the inheritance underpinnings of syndromic and non-syndromic polydactylies and highlights dactyly presentations with unknown genetic roots. This review summarizes the current information and genetics-enhanced understanding of polydactyly.

BACKGROUND

There is a frequency of 0.37 to 1.2 per 1000 live births for polydactyly, which is also known as hyperdactyly. It is characterized by the presence of extra fingers. Polydactyly is caused by a failure in limb development, specifically the patterning of the developing limb bud. The phenotypic and genetic variability of polydactyly makes its etiology difficult to understand. Pre-axial polydactyly, central polydactyly (axial), and postaxial polydactyly are all examples of non-syndromic polydactyly (ulnar). An autosomal dominant disorder with varying penetrance that is mostly passed down via limb development patterning abnormalities.

METHOD

A comprehensive search of MEDLINE/PubMed and other databases was followed by an evaluation of the relevant papers, with a particular focus on those published between 2000 and 2022.

RESULTS

Of 747 published article related to Polydactyly from MEDLINE/PubMed search, 43 were from the last 10 years and were the focus of this review.

CONCLUSION

Polydactyly is one of the most frequent congenital hand malformations. PAP is more common than PPD, whereas central polydactyly is very uncommon.

The molecular genetics of human appendicular skeleton

Disorders that result from de-arrangement of growth, development and/or differentiation of the appendages (limbs and digit) are collectively called as inherited abnormalities of human appendicular skeleton. The bones of appendicular skeleton have central role in locomotion and movement. The different types of appendicular skeletal abnormalities are well described in the report of "Nosology and Classification of Genetic skeletal disorders: 2019 Revision". In the current article, we intend to present the embryology, developmental pathways, disorders and the molecular genetics of the appendicular skeletal malformations. We mainly focused on the polydactyly, syndactyly, brachydactyly, split-hand-foot malformation and clubfoot disorders. To our knowledge, only nine genes of polydactyly, five genes of split-hand-foot malformation, nine genes for syndactyly, eight genes for brachydactyly and only single gene for clubfoot have been identified to be involved in disease pathophysiology. The current molecular genetic data will help life sciences researchers working on the rare skeletal disorders. Moreover, the aim of present systematic review is to gather the published knowledge on molecular genetics of appendicular skeleton, which would help in genetic counseling and molecular diagnosis.

First record of polydactyly for a European bat, Myotis daubentonii (Chiroptera, Vespertilionidae)

Despite being one of the most common congenital hand abnormalities in humans, polydactyly remains extremely rare in bats. To date, it has been observed only in two insectivorous families in North America (Molossidae and Vespertilionidae) and a single case for the New World fruit bats (Phyllostomidae). We report the first case of polydactyly in a European bat – a Myotis daubentonii (Vespertilionidae), with eight toes. The bat was found alive, hibernating in the Natura 2000 site (PLH080003 “Nietoperek”) in Poland.

Novel heterozygous sequence variant in the GLI1 underlies postaxial polydactyly

Polydactyly is one of the most common congenital abnormal phenotype of autopod, which is characterized by extra supernumerary digit in hands/feet with or without well-developed bony structure within the digits. Preaxial polydactyly (PPD), postaxial polydactyly (PAP), and meso-axial (central) polydactyly are three different isoforms of polydactyly. Genetically, at least 10 genes have been identified causing nonsyndromic polydactyly. In the present study, we have investigated a large family segregating autosomal dominant form of nonsyndromic polydactyly. Whole exome sequencing followed by Sanger sequencing revealed a novel heterozygous missense variant (NM_005269.3; c.1064C>A; p.(Thr355Asn) in the gene GLI1 segregating with the disease phenotype within the family. This study presents first familial case of autosomal dominant form of polydactyly caused by the GLI1 variant.

Isolated hexadactylia: A rare case of central polydactyly of the foot

BACKGROUND

Central polydactyly of foot is uncommon form of polydactyly but it usually causes intermetatarsal widening because of metatarsal bifurcation. Central polydactyly associated with T shaped bifurcation of metatarsal in vertical plane has not been reported yet.

CASE

We present a 4 year male child with extra toe on the dorsal aspect of right foot with complains of difficulty in wearing footwear and poor cosmesis. The extra digit was fully developed with bifurcation of 2^nd metatarsal bone proximal to the head without any intermetatarsal widening. The angular deviation was 45° to the longitudinal axis of foot and in a plane vertical to the transverse arch of foot. The child was operated with excision of extra toe without any residual bony deformity.

CONCLUSION

The central polydactyly is rare type of polydactyly of foot. Central polydactyly with metatarsal extension causing intermetatarsal widening has been well described entity. But the previous classifications need to be modified to include central polydactyly with vertical oriented T bifurcation of metatarsal bone without intermetatarsal widening.

FAM92A Underlies Nonsyndromic Postaxial Polydactyly in Humans and an Abnormal Limb and Digit Skeletal Phenotype in Mice

Polydactyly is a common congenital anomaly of the hand and foot. Postaxial polydactyly (PAP) is characterized by one or more posterior or postaxial digits. In a Pakistani family with autosomal recessive nonsyndromic postaxial polydactyly type A (PAPA), we performed genomewide genotyping, linkage analysis, and exome and Sanger sequencing. Exome sequencing revealed a homozygous nonsense variant (c.478C>T, p.[Arg160*]) in the FAM92A gene within the mapped region on 8q21.13-q24.12 that segregated with the PAPA phenotype. We found that FAM92A is expressed in the developing mouse limb and E11.5 limb bud including the progress zone and the apical ectodermal ridge, where it strongly localizes at the cilia level, suggesting an important role in limb patterning. The identified variant leads to a loss of the FAM92A/Chibby1 complex that is crucial for ciliogenesis and impairs the recruitment and the colocalization of FAM92A with Chibby1 at the base of the cilia. In addition, we show that Fam92a^-/- homozygous mice also exhibit an abnormal digit morphology, including metatarsal osteomas and polysyndactyly, in addition to distinct abnormalities on the deltoid tuberosity of their humeri. In conclusion, we present a new nonsyndromic PAPA ciliopathy due to a loss-of-function variant in FAM92A. © 2018 American Society for Bone and Mineral Research.

Clinical Genetics of Polydactyly: An Updated Review

Polydactyly, also known as hyperdactyly or hexadactyly is the most common hereditary limb anomaly characterized by extra fingers or toes, with various associated morphologic phenotypes as part of a syndrome (syndromic polydactyly) or may occur as a separate event (non-syndromic polydactyly). Broadly, the non-syndromic polydactyly has been classified into three types, i.e.; preaxial polydactyly (radial), central polydactyly (axial), and postaxial polydactyly (ulnar). Mostly inherited as an autosomal dominant entity with variable penetrance and caused by defects that occur in the anterior-posterior patterning of limb development. In humans, to-date at least 10 loci and six genes causing non-syndromic polydactyly have been identified, including the ZNF141, GLI3, MIPOL1, IQCE, PITX1, and the GLI1. In the present review, clinical, genetic and molecular characterization of the polydactyly types has been presented including the recent genes and loci identified for non-syndromic polydactyly. This review provides an overview of the complex genetic mechanism underlie polydactyly and might help in genetic counseling and quick molecular diagnosis.

GLI3-related polydactyly: a review

GLI3 mutations are known to be associated with nine syndromes/conditions in which polydactyly is a feature. In this review, the embryology, pathogenesis, and animal models of GLI3-related polydactyly are discussed first. This is followed by a detailed review of the genotype-phenotype correlations. Based on our review of the literature and our clinical experiences, we recommend viewing GLI3-related syndromes/conditions as four separate entities; each characterized by a specific pattern of polydactyly. These four entities are: the preaxial polydactyly type IV-Greig-acrocallosal spectrum, postaxial polydactyly types A/B, Pallister-Hall syndrome (PHS), and oral-facial-digital overlap syndrome. We also provide illustrative clinical examples from our practice including a family with a novel GLI3 mutation causing PHS. The review also introduces the term 'Forme Fruste' preaxial polydactyly and gives several conclusions/recommendations including the recommendation to revise the current criteria for the clinical diagnosis of PHS.

Advances in the molecular genetics of non-syndromic polydactyly

Polydactyly is one of the most common inherited limb abnormalities, characterised by supernumerary fingers or toes. It results from disturbances in the normal programme of the anterior-posterior axis of the developing limb, with diverse aetiology and variable inter- and intra-familial clinical features. Polydactyly can occur as an isolated disorder (non-syndromic polydactyly) or as a part of an anomaly syndrome (syndromic polydactyly). On the basis of the anatomic location of the duplicated digits, non-syndromic polydactyly is divided into three kinds, including preaxial polydactyly, axial polydactyly and postaxial polydactyly. Non-syndromic polydactyly frequently exhibits an autosomal dominant inheritance with variable penetrance. To date, in human, at least ten loci and four disease-causing genes, including the GLI3 gene, the ZNF141 gene, the MIPOL1 gene and the PITX1 gene, have been identified. In this paper, we review clinical features of non-syndromic polydactyly and summarise the recent progress in the molecular genetics, including loci and genes that are responsible for the disorder, the signalling pathways that these genetic factors are involved in, as well as animal models of the disorder. These progresses will improve our understanding of the complex disorder and have implications on genetic counselling such as prenatal diagnosis.

A classification system for ulnar polydactyly and clinical series

PURPOSE

To describe a modified classification that includes both complicated ulnar polydactyly and ulnar polydactyly with bifid or duplicated proximal phalanx and to apply it to a clinical series.

METHODS

A total of 42 patients with ulnar polydactyly were admitted to our outpatient clinic between January 2004 and January 2014 and were included in the study. Patients' clinical and radiological data were evaluated retrospectively and organized into 5 different subgroups.

RESULTS

There were 20 bilateral and 22 unilateral patients with polydactyly. These were composed of 32 supernumerary digits represented as type I, 7 as type II, 9 as type III, 12 as type IV, and 2 as type V. Nine patients had bifid or duplicated proximal phalanges (types IIIA and IIIB) and 2 were of the complicated type (type V). We identified 5 types based on morphology, level of duplication, and other complicating features.

CONCLUSIONS

Complicated ulnar polydactyly and ulnar polydactyly with bifid proximal phalanx are 2 important types of ulnar polydactyly with surgical implications, both separately included in the Pritsch classification system and Rayan and Al-Qattan classification systems. None of the current classification systems include both types. We believe our modified classification system will help to better define diagnosis and treatment plans for bifid proximal phalanx and complicated type ulnar polydactyly.

TYPE OF STUDY/LEVEL OF EVIDENCE

Diagnostic III.

Prenatal diagnosis of a 7q21.13q22.1 deletion detected using high-resolution microarray

We report a case of de novo 7q interstitial deletion detected by conventional karyotyping and by microarray of amniotic fluid sampled during the prenatal period. A 32-year-old pregnant woman was evaluated at our hospital following detection of increased nuchal translucency at 12 weeks and 5 days of gestation. Conventional karyotyping revealed 46,XX,del(7)(q21q22) in 20 interphase mitotic cells, and high-resolution microarray revealed 12.8 Mb (90,625,014-103,430,901) deletion in the region 7q21.13q22.1. Both parents had normal karyotypes. After birth, the neonate displayed several anomalies, including palatine cleft, upslanted and wide palpebral fissure, low-set ears, micrognathia, microcephaly, ventriculomegaly, subglottic tracheal stenosis, hearing loss, and hand/foot deformities, including brachydactyly, polydactyly, and cutaneous syndactyly. This case study helps explain the phenotype-genotype relationship in patients with 7q21.13q22.1 deletion.

Ulnar polydactyly - an analysis of appearance and postoperative outcome

BACKGROUND/PURPOSE

Ulnar polydactylies present with a wide variation in the size and appearance of the affected finger, ranging from small cutaneous appendages to fully formed additional fingers. Since ulnar polydactyly is rarely associated with functional disabilities, psychological and cosmetic reasons are the main rationale for surgical treatment. The aim of this study was to present the appearance, treatment regimen, and outcome of a series of children treated with ulnar polydactylies.

METHODS

Data of all pediatric patients treated between 2000 and 2010 were included. For assessing long-term outcome, patients were contacted via mail and asked to complete a questionnaire concerning location and appearance of the scar as well as functional and cosmetic satisfaction (VAS 0-100).

RESULTS

In that period, 32 patients (20 male, 12 female) with 53 ulnar polydactylies were treated. In 20 patients the polydactyly occurred bilaterally (63%), in 10 patients on the left side (31%), and 2 patients presented with right-sided ulnar polydactyly (6%). The vast majority of ulnar polydactylies were floating cutaneous appendages. The mean age of the patients at operation was 8.6 months (range 0 to 10 years). 20 patients (63%) responded to the postal questionnaire. Follow-up time was 4.9 years (range 2.1 to 10 years). The majority of patients reported a flat scar (n=18, 90%). Mean overall satisfaction with the postoperative result using a VAS 0-100 score was 89.

CONCLUSION

We were able to report a good postoperative outcome of a series of patients suffering from ulnar polydactylies.

Type A ulnar polydactyly of the hand: a classification system and clinical series

PURPOSE

To propose a classification system for type A ulnar polydactyly based on radiographic findings and characterize the demographic features of patients with these deformities.

METHODS

We identified 49 patients with type A ulnar polydactyly of the hand who were seen in our institution over 20 years. Patients' medical records and radiographs were retrospectively reviewed and used to distinguish morphological subtypes.

RESULTS

Ninety-six percent of the deformities (64/67) were allocated to 1 of the 5 subgroups of our suggested classification, and the type that originated from the metacarpophalangeal joint was the most common. Sixty-nine percent of patients in our series (34/49) had either bilateral type A or a contralateral type B ulnar polydactyly, and 63% (31/49) had ulnar polydactyly of one or both feet. Twenty-four percent of patients (12/49) had associated syndromes or congenital anomalies involving areas other than the hand or foot. The most common syndrome associated with type A ulnar polydactyly was chondroectodermal dysplasia (n = 3). Sixty-five percent of the patients (32/49) were Caucasian, 20% were Hispanic (10/49), 12% were African American (6/49), and one was Asian. The percentage of African Americans in our series was similar to that in the general patient population seen in our institution.

CONCLUSIONS

The majority of type A ulnar polydactyly can be classified into 1 of 5 morphological subtypes that have potential clinical relevance regarding surgical treatment. In patients with type A ulnar polydactyly, contralateral hand and foot polydactyly is frequent. Associated congenital anomalies and syndromes can also be present.

An unusual case of fibular (postaxial) polydactyly: extrametatarsal head with fused duplication of the proximal phalanx

Polydactyly of the foot is a congenital anomaly characterized by the appearance of all or part of 1 or more additional rays. A number of morphologically and anatomically based classifications exist. We present an unusual case of fibular (postaxial) polydactyly characterized by an extrametatarsal head with fused duplication of the proximal phalanx. We describe the method of surgical correction and emphasize the need for careful preoperative planning to achieve a good functional and cosmetic outcome.

The clinical features of ulnar polydactyly in a middle eastern population

Two clinical forms of ulnar polydactyly are recognised in the literature, viz the African and the Caucasian forms. The current study investigated the clinical and radiological features of ulnar polydactyly in 94 Saudi patients. The incidence of ulnar polydactyly was one in 1000 live births. There were 41 males and 53 females. Positive family history, syndromal cases, associated hand anomalies, polydactyly of the little toe and systemic abnormalities were seen in 11%, 6%, 5%, 29% and 23% of cases, respectively. There were 50 unilateral (53%) and 44 bilateral cases (47%). In unilateral cases, the left hand was more commonly affected. Using a modified Rayan-Frey classification, the majority of cases were classified as Type II (pedunculated polydactyly, 52 (55%) cases) and Type III (a functioning and articulating extra digit without complete duplication of the metacarpal, 29 (31%) cases). It was concluded that the Saudi clinical presentation of ulnar polydactyly is somewhat different epidemiologically and lies between the African and Caucasian forms.

Microcephaly, distinctive facies, single atrium, postaxial polydactyly, skeletal defects and mental retardation: a new familial faciocardiomelic syndrome?

Three siblings with postaxial polydactyly type A, congenital heart defect (single atrium), mental retardation, microcephaly, a distinctive facial appearance, skeletal anomalies and neonatal macrosomy were studied. Comparison with other cardiomelic syndromes previously described in the literature lead us to conclude that this is a new faciocardiomelic syndrome probably inherited as an autosomal recessive trait.

Uniparental disomy (UPD) other than 15: Phenotypes and bibliography updated

Uniparental disomy (UPD) describes the inheritance of a pair of chromosomes from only one parent. The concept was introduced in Medical Genetics by Engel (1980); Am J Med Genet 6:137-143. Aside UPD 15, which is the most frequent one, up to now (February 2005) 197 cases with whole chromosome maternal UPD other than 15 (124 X heterodisomy, 59 X isodisomy, and 14 cases without information of the mode of UPD) and 68 cases with whole chromosome paternal UPD other than 15 (13 X heterdisomy, 53 X isodisomy, and 2 cases without information of the mode of UPD) have been reported. In this review we discuss briefly the problems associated with UPD and provide a comprehensive clinical summary with a bibliography for each UPD other than 15 as a guide for genetic counseling.