Classifications in Brief: The Wassel Classification for Radial Polydactyly

Epidemiology of congenital polydactyly and syndactyly in Hunan Province, China

OBJECTIVE

To describe the prevalence and epidemiology of congenital polydactyly and syndactyly in Hunan Province, China, 2016-2020.

METHODS

Data were obtained from the Birth Defects Surveillance System in Hunan Province, China, 2016-2020. Prevalence of birth defects (polydactyly or syndactyly) is the number of cases per 1000 births (unit: ‰). Prevalence and 95% confidence intervals (CI) were calculated by the log-binomial method. Chi-square trend tests (χ2trend) were used to determine trends in prevalence by year. Crude odds ratios (ORs) were calculated to examine the association of each demographic characteristic with polydactyly and syndactyly.

RESULTS

Our study included 847,755 births, and 14,459 birth defects were identified, including 1,888 polydactyly and 626 syndactyly cases, accounting for 13.06% and 4.33% of birth defects, respectively. The prevalences of total birth defects, polydactyly, and syndactyly were 17.06‰ (95%CI: 16.78-17.33), 2.23‰ (95%CI: 2.13-2.33), and 0.74‰ (95%CI: 0.68-0.80), respectively. Most polydactyly (96.77%) and syndactyly (95.69%) were diagnosed postnatally (within 7 days). From 2016 to 2020, the prevalences of polydactyly were 1.94‰, 2.07‰, 2.20‰, 2.54‰, and 2.48‰, respectively, showing an upward trend (χ2trend = 19.48, P < 0.01); The prevalences of syndactyly were 0.62‰, 0.66‰, 0.77‰, 0.81‰, and 0.89‰, respectively, showing an upward trend (χ2trend = 10.81, P = 0.03). Hand polydactyly (2.26‰ vs. 1.33‰, OR = 1.69, 95%CI: 1.52-1.87) and hand syndactyly (0.43‰ vs. 0.28‰, OR = 1.42, 95%CI: 1.14-1.76) were more common in males than females. Polydactyly (2.67‰ vs. 1.93‰, OR = 1.38, 95%CI: 1.26-1.51) and syndactyly (0.91‰ vs. 0.62‰, OR = 1.47, 95%CI: 1.26-1.72) were more common in urban areas than in rural areas. Compared to maternal age 25-29, hand polydactyly was more common in maternal age < 20 (2.48‰ vs. 1.74‰, OR = 1.43, 95%CI: 1.01-2.02) or ≥ 35 (2.25‰ vs. 1.74‰, OR = 1.30, 95%CI: 1.12-1.50).

CONCLUSION

In summary, we have described the prevalence and epidemiology of polydactyly and syndactyly from hospital-based surveillance in Hunan Province, China, 2016-2020. Our findings make some original contributions to the field, which may be valuable for future research.

Intraoperative Observation of the Proper Digital Nerves in Wassel-Flatt Type Ⅳ Radial Polydactyly

PURPOSE

The aim of the study was to present the intraoperative findings of the relevant digital nerves of the duplicated thumbs in an excision and reconstruction procedure for the Wassel-Flatt type Ⅳ radial polydactyly.

METHODS

The study was conducted on patients with Wassel-Flatt type IV radial polydactyly who underwent excision and reconstruction between 2018 and 2021 at our institution. The ulnar digital nerve of the radial thumb and the radial digital nerve of the ulnar thumb were identified and traced intraoperatively. The level of the bifurcation of the nerves and abnormal findings were documented.

RESULTS

A total of 123 hands in 119 patients were included in this study. In 114 hands, the bifurcation of the nerves was located within 1 cm of the metacarpophalangeal flexion crease. The radial digital nerve to the ulnar thumb was abnormally compressed in deep fascial tissue in 7 of these 114 hands. In 5 hands, the level of bifurcation was more than 1 cm proximal to the crease. No radial digital nerve to the ulnar thumb was identified in the remaining 4 hands.

CONCLUSIONS

Although rare, abnormal nerve compression of the digital nerve may exist in duplicated thumbs of Wassel-Flatt type IV radial polydactyly.

CLINICAL RELEVANCE

In an excision and reconstruction procedure, we suggest that the bifurcation of the nerves should be identified before the nerve to the radial thumb is excised to avoid injuring the nerve to the main ulnar thumb.

Congenital Upper-Limb Differences: A 6-Year Literature Review

➤ The Oberg-Manske-Tonkin (OMT) classification of congenital hand and upper-limb anomalies continues to be refined as our understanding of the genetic and embryonic etiology of limb anomalies improves.➤ We have conducted an evaluation of graft and graftless techniques for syndactyly reconstruction; strengths and drawbacks exist for each technique.➤ Treatment for radial longitudinal deficiency remains controversial; however, radialization has shown promise in early follow-up for severe deformities.➤ Recent emphasis on psychosocial aspects of care has demonstrated that children with congenital upper-limb differences demonstrate good peer relationships and marked adaptability.

Tourniquet-Related Nerve Injury Following Reconstructive Surgery for Wassel Type IV Preaxial Polydactyly of 13-Year-Old Boy: A Case Report

BACKGROUND Congenital thumb duplication comes under the Wassel type IV classification is the hypoplastic variety, with the extra digit growing from the dominant thumb's soft tissue alone. Excising the hypoplastic finger while reconstructing for the retained one has been the most adopted approach. Tourniquets are commonly utilized tools in orthopedic surgeries to reduce the amount of blood, thus enhancing the visibility. Unfortunately, tourniquet-related nerve injury (TNRI) is gaining more attention as a serious complication of tourniquet use in surgery. CASE REPORT A 13-year-old Asian boy with preaxial polydactyly Wassel type IV of the right hand underwent reconstruction surgery. A pneumatic tourniquet was applied at 200 mmHg on the right mid-upper arm and maintained for 90 min. After the surgery, the patient had total weakness with numbness, tingling, and burning sensation from his right upper arm to his fingertips. The neurological examination and nerve conduction studies (NCS) results were consistent with axonotmesis lesions. Pharmacological and physical rehabilitation therapy had successfully restored full motoric and sensory function after 6 months. CONCLUSIONS Nerve injury should be acknowledged as a possible complication from routinely-utilized tourniquets in orthopedic surgeries. Our cases may expand the need for further studies to establish a guideline for tourniquet use and TRNI management.

A Rare Combination of Heptadactyl and Hexadactyl Polydactyly in a Neonate

Heptadactyly and hexadactyly are rare congenital disorders from the polydactyly family. This type of polydactyly is usually classified into three major groups: preaxial (medial ray), postaxial (lateral ray), and central polydactyly. The most common presentation is both preaxial and postaxial polydactyly. The occurrence of heptadactyly and hexadactyly has been reported but the presence of both in the same infant has not been reported yet. We report the presence of both these abnormalities in the same infant.

Prediction of Surgical Outcomes of Radial Polydactyly From the Wassel-Flatt Type and Symmetry of Duplication

BACKGROUND

The Wassel classification is commonly used for cases of radial polydactyly but has not been used to predict surgical outcomes. This study aimed to investigate the predictive factors of surgical outcomes using the Wassel type and symmetry of duplication.

METHODS

Forty-five patients with 47 radial polydactylies were reviewed using the Japanese Society for Surgery of the Hand (JSSH) scores 4.6 years after minor thumb excision and reconstructive surgery. The symmetry index was defined as the metaphyseal width ratio of the minor thumb to the dominant thumb. The relationships between the JSSH scores and operation age, sex, side, follow-up duration, Wassel type, symmetric index, divergent angle, and joint angulation were analyzed by linear regression.

RESULTS

The mean JSSH score of the 47 thumbs was 18.3 points (range, 15-20). Five thumbs had fair or poor outcomes (scores <17), all of which were Wassel type IV. The hypoplastic type had a better JSSH score (19.4) than other Wassel types. The symmetric index had a negative relationship with JSSH scores, especially for Wassel type IV (r=-0.68, P =0.001). Linear regression revealed that the symmetric index was the only independent factor significantly associated with JSSH scores among Wassel type IV polydactylies ( P <0.05). The receiver operating characteristic curve suggested a symmetric index <0.74 could predict good or excellent outcomes.

CONCLUSION

The symmetry of the 2 duplicated thumbs is an important factor for surgical outcomes. The Wassel type IV polydactylies with a symmetric index >0.74 are at greater risk of fair or poor outcomes after excision and reconstruction, and further studies are warranted to confirm whether the Bilhaut-Cloquet procedure is a good choice.

LEVEL OF EVIDENCE

Level IV-Case-control study.

Factors affecting hand cosmesis and the aesthetic impact of surgery on congenital hand differences in Finland

We assessed the appearance and cosmetic impact of surgery in congenitally different hands in Finland. A questionnaire was sent to 1165 respondents (786 female) with a mean age of 33 years (range 3-84). Participants were shown nine image pairs and seven pairs of pre- and postoperative images twice in a random order and asked to choose the more cosmetically pleasing one. We found that the appearance and number of fingers had an important aesthetic role, with higher number and more normal appearing digits consistently scoring higher than its counterpart (range 59-99%). Postoperative appearances were perceived as better than preoperative ones in syndactyly (98%), thumb duplication (92%), cleft hand (93%) and radial dysplasia (99%). Toe transfer and pollicization had little impact on cosmesis. This study demonstrated that surgery could improve cosmesis in congenitally different hands and overall, most respondents prefer an appearance that is as close as possible to normality. Level of evidence: IV.

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.

Genetics of congenital anomalies of the hand

Congenital anomalies of the hand are malformations occurring during the development of the human limb, and present as isolated disorders or as a part of a syndrome. During the last years, molecular analysis techniques have offered increasing knowledge about the molecular basis of hand malformations. Disturbances in the signaling pathways during the development of the upper limb result in malformations of the upper extremity. At present, several genes have been identified as responsible for hand anomalies and other have been recognized as suspect genes related to them. Different and new high throughput methods have been introduced for the identification of the gene mutations. In the current editorial, we summarize concisely the current molecular status of isolated hand genetic disorders and the recent progress in molecular genetics, including the genes related to the disorder. This progress improves the knowledge of these disorders and has implications on genetic counselling and prenatal diagnosis.

Radial Polydactyly

» Radial polydactyly is one of the most common congenital anomalies of the hand, with an incidence of 0.08 to 1.40 per 1,000 live births; it requires surgical treatment early in life.» Polydactyly occurs during weeks 5, 6, 7, and 8 of embryogenesis, principally due to misregulation of the sonic hedgehog protein within the developing limb bud.» The Flatt classification system of preaxial polydactyly (types I to VII), as published by Wassel, categorizes preaxial polydactyly based on osseous abnormalities, but it has substantial limitations.» For improved function and appearance, preaxial polydactyly ideally requires surgical intervention at an early age (between 1 and 2 years of age) before the development of fine motor skills.

[Soft tissue balance technique by flexor pollicis longus tendon transfer for Wassel -D thumb duplication in children]

Objective

To investigate the effectiveness of soft tissue balance technique by flexor pollicis longus (FPL) tendon transfer for Wassel Ⅳ-D thumb duplication in children.

Methods

A clinical data of 14 children with Wassel Ⅳ-D thumb duplication met the selection criteria between January 2017 and January 2021 was retrospectively analyzed. There were 5 boys and 9 girls with an average age of 21.6 months (range, 18-35 months). Ten cases were left hand deformity and 4 cases were right hand deformity. During operation, the radial thumb was excised, and the FPL tendon of the radial thumb was used to reconstruct the soft tissue balance of the ulnar thumb. Postoperative evaluation included the range of motion (ROM) of passive flexion and extension of the interphalangeal joint (IP) and metacarpophalangeal joint (MCP), the alignments of the IP and MCP, the percentage of the width of the nail plate and the circumference of the thumb at the level of the IP to contralateral thumb.

Results

All operations were completed successfully, and all incisions healed by first intention. The children were followed up 12-36 months (mean, 21.7 months). At last follow-up, the ROM of passive flexion and the deviation of the IP, and the deviation of the MCP significantly improved when compared with those before operation (P<0.05); the ROM of passive extension of the IP and the ROM of passive flexion of the MCP did not significantly improve when compared with those before operation (P>0.05). The ROMs of passive extension of the MCP were 0° before and after operation. The width of the nail plate was 76.6%±4.1% of the unaffected side, and the circumference of the thumb at the level of the IP was 92.0%±9.1% of the unaffected side.

Conclusion

The soft tissue balance technique by FPL tendon trasfer can effectively correct the alignment of the Wassel Ⅳ-D thumb duplication in children, and maintain the correction effect effectively, but further follow-up and comprehensive evaluation are needed to investigate the long-term effectiveness.

Epidemiological characteristics and distribution of congenital thumb duplication in south China: An analysis of 2,300 thumbs in 2,108 children

OBJECTIVE

The objective of this study was to evaluate epidemiological and anatomical characteristics of children with congenital thumb duplication (CTD).

METHODS

We retrospectively reviewed 2108 children with CTD. Data regarding sex, age at the surgery, laterality, uni- or bilateral involvement, and dominant side were retrieved from the medical charts. Plain radiographs were used to classify all CTD according to Wassel-Flatt, Rotterdam and Chung classification systems and to evaluate the patho-anatomy of the duplication as well as the presence of associated anomaly.

RESULTS

A total of 796 girls and 1,312 boys with CTD (n = 2,300 thumbs) met the inclusion criteria. The male to female and unilateral to bilateral ratio were 1.6:1 and 10:1, respectively. Associated anomaly was found in 238/2108 patients (11.3%), and the middle phalanx deformity of the 5th finger was the most common one. A dominant thumb, larger and more developed, was on the ulnar side in 2270/2,300 cases (98.7%).According to the Wassel-Flatt classification, type IV (40.2%) was the most common deformity and the extra thumb was connected to the main thumb by a joint in most cases (437/780); overall, 15.7% of thumbs (n = 360) did not fit the Wassel-Flatt classification.According to the Rotterdam classification, type IV (51.3%) was the most common form; in most cases (363/1180) the thumb was hypoplastic or floating. Overall, 3/2,300 thumbs (0.1%) could not be classified according to Rotterdam classification.According to the Chung classification, type A was the most common subtype (44.1%); in most cases (716/1015) the duplication was at the level of the metacarpal bone. Overall, 2/2,300 thumbs (0.1%) did not fit the Chung classification.

CONCLUSIONS

In patients from southern China, CTD shows male and right-sided predominance with ulnar-dominant thumb. Abnormalities of the middle phalanx of the 5th finger are more frequent in patients with associated anomaly. The development of a simple and comprehensive classification system is needed to guide treatment and to adequately assess the epidemiological characteristics of patients with CTD in order to facilitate comparison between different patients' populations.

LEVEL OF EVIDENCE

III.

A Novel Homozygous Missense Mutation in the Zinc Finger DNA Binding Domain of GLI1 Causes Recessive Post-Axial Polydactyly

Background: Polydactyly is a prevalent digit abnormality characterized by having extra digits/toes. Mutations in eleven known genes have been associated to cause nonsyndromic polydactyly: GLI3, GLI1, ZRS regulating LMBR1, IQCE, ZNF141, PITX1, MIPOL1, FAM92A, STKLD1, KIAA0825, and DACH1. Method: A single affected family member (IV-4) was subjected to whole-exome sequencing (WES) to identify the causal gene. Bi-directional Sanger sequencing was performed to segregate the identified variant within the family. In silico analysis was performed to investigate the effect of the variant on DNA binding properties. Results: whole-exome sequencing identified a bi-allelic missense variant (c.1010C > T; p. Ser337Leu) in exon nine of GLI1 gene located on chromosome 12q13.3. With the use of Sanger sequencing, the identified variant segregated perfectly with the disease phenotype. Furthermore, in silico analysis of this DNA binding protein revealed that the variant weakened the DNA binding interaction, resulting in indecorous GLI1 function. Conclusion: Herein, we report a novel variant in GLI1 gene, causing autosomal recessive post-axial polydactyly type A (PAPA) type 8. This confirms the critical role of GLI1 in digit development and might help in genotype-phenotype correlation in the future.

Polydactyly of the thumb: a modification of the Wassel-Flatt classification

Although the Wassel-Flatt classification system has been widely used for radial polydactyly, it has some limitations. We modified the classification system by introducing the hypoplastic types and refining the definition of triphalangeal thumb without changing the main structure of the original classification system. A total of 200 consecutive duplicated thumbs of 183 patients treated surgically from June 2016 to June 2018 were included. We evaluated intra-observer and inter-observer reliability using the kappa coefficient in the modified and original Wassel-Flatt classification systems (three examiners evaluated each case twice, with an interval of 4 weeks). We also evaluated the surgical methods according to the types of deformity in the modified and original Wassel-Flatt classification systems. The modified Wassel-Flatt classification system had good inter-observer reliability and provides useful information for determining the surgical plan according to the types of radial polydactyly.Level of evidence: IV.

Thumb duplication/polydactyly

A significant lesson for those assessing the work of others stems from the necessity to review what has been written before. It remains a common but human error to misinterpret or misrepresent the words of others and indeed, for inconsistencies in these to become apparent. This is certainly so in the field of congenital hand surgery and especially so with discussion of thumb duplication/polydactyly. Many of the presentations in this journal issue deal with the subject of thumb duplication. All involve a consideration of classification despite an emphasis on investigative measures and techniques in some. For ease of reading, I will place my comments on these articles within the categories of classification, investigations assisting management decisions and alternative techniques, though the contents of each article are not necessarily restricted to these categories.

A Comparative Analysis of 150 Thumb Polydactyly Cases from the CoULD Registry Using the Wassel-Flatt, Rotterdam, and Chung Classifications

PURPOSE

Three commonly used classifications for thumb polydactyly are the Wassel-Flatt, Rotterdam, and Chung. The ideal classification system would have high validity and reliability and be descriptive of the thumb anomaly. The purposes of this investigation were to (1) compare the inter- and intrarater reliability of these 3 classifications when applied to a large sample of patients enrolled in the Congenital Upper Limb Differences (CoULD) Registry and (2) determine the prevalence of radial polydactyly types when using the various classifications in a North American population.

METHODS

Inter- and intrarater reliability were determined using 150 cases of radial polydactyly presented in a Web-based format to 7 raters in 3 rounds, a preliminary training round and 2 observation rounds. Raters classified each case according to the Wassel-Flatt, Rotterdam, and Chung classifications. Inter- and intrarater reliability were evaluated with the intraclass correlation coefficient (ICC) calculated using 2-way random measures with perfect agreement.

RESULTS

For Wassel-Flatt, both the interrater (ICC, 0.93) and the intrarater reliability (ICC, 0.91) were excellent. The Rotterdam classification had excellent reliability for both interrater reliability (ICC, 0.98) and intrarater reliability (ICC, 0.94), when considering type alone. Interrater analysis of the additional subtypes demonstrated a wide range of reliabilities. The Chung classification had good interrater (ICC, 0.88) and intrarater reliability (ICC, 0.77). Within the Wassel-Flatt classification, the most frequent unclassifiable thumb was a type IV hypoplastic thumb as classified by the Rotterdam classification.

CONCLUSIONS

The Wassel-Flatt and Rotterdam classifications for radial polydactyly have excellent inter- and intrarater reliability. Despite its simplicity, the Chung classification was less reliable in comparison. The Chung and Rotterdam classification systems capture the hypoplastic subtypes that are unclassifiable in the Wassel-Flatt system. Addition of the hypoplastic subtype to the Wassel-Flatt classification (eg, Wassel-Flatt type IVh) would maintain the highest reliability and classify over 90% of thumbs deemed unclassifiable in the Wassel-Flatt system.

CLINICAL RELEVANCE

The Wassel-Flatt and Rotterdam classifications have excellent inter-and intrarater reliability for the hand surgeon treating thumb polydactyly. Addition of a hypoplastic subtype to the Wassel-Flatt (Type 4h) allows classification of most previously unclassifiable thumbs.

Clinical Characteristics and Distribution of Thumb Polydactyly in South China: A Retrospective Analysis of 483 Hands

PURPOSE

This study was intended to characterize the epidemiological features of thumb polydactyly (TP) in South China.

METHODS

Clinical records were retrieved from 1 central hospital in South China to identify the patients with a definite diagnosis of TP from January 2004 to January 2017. The cases were classified by their x-ray appearance. The data collected included sex, age at first operation, reoperation, family history, unilateral/bilateral polydactyly, right/left hand involvement in unilateral cases, classification of polydactyly, and the presence of associated congenital anomalies.

RESULTS

A total of 428 patients with a definite diagnosis of TP were identified (278 males and 150 females) involving 483 cases, 373 unilateral and 55 bilateral. A syndrome or associated congenital anomaly was found in 26 (18 unilateral and 8 bilateral cases). A dominant thumb, larger and more developed, was observed in 448 hands (93%), and was the ulnar thumb in 433. Owing to postoperative complications, 31 thumbs (6.4%) underwent reoperation. The average interval from initial surgery to reoperation was 4.8 years.

CONCLUSIONS

Thumb polydactyly had a male predominance in this Chinese cohort, mostly occurring on the right hand with an ulnar dominant thumb. Bilateral cases had a higher incidence of associated anomaly and positive family history than unilateral cases. The need for additional surgery for TP might occur as late as 4.8 years after primary surgery.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Congenital Deformities of the Hands

Evaluation of the pediatric musculoskeletal system may be difficult because of differences between children and adults. As children mature, their physical structure approaches that of an adult. However, in the meantime, varying stages of ossification and developmental timelines may confuse the average clinician. Congenital abnormalities of the upper extremity are extremely numerous, but here we present 10 that often are seen in clinical practice. The article discusses the diagnosis, evaluation, treatment, and outcomes of each condition.

Congenital thumb differences- current concepts

Anomalies of the thumb development are not uncommon and may be associated with a number of syndromes also. These anomalies range from total absence to duplication. Reconstructive surgery for the creation of an opposable thumb is the most rewarding aspect of Hand Surgery and also the most challenging. Classification systems have been modified for better description. A number of procedures have been introduced to improve the functionality of the hand in anomalies and age old concepts are undergoing a metamorphosis to further this. A brief description of the common conditions and their treatment are discussed here and highlighted by selected clinical cases.

A novel ZRS variant causes preaxial polydactyly type I by increased sonic hedgehog expression in the developing limb bud

Purpose

Preaxial polydactyly (PPD) is a common congenital hand malformation classified into four subtypes (PPD I–IV). Variants in the zone of polarizing activity regulatory sequence (ZRS) within intron 5 of the LMBR1 gene are linked to most PPD types. However, the genes responsible for PPD I and the underlying mechanisms are unknown.

Methods

A rare large four-generation family with isolated PPD I was subjected to genome-wide genotyping and sequence analysis. In vitro and in vivo functional studies were performed in Caco-2 cells, 293T cells, and a knockin transgenic mouse model.

Results

A novel g.101779T>A (reference sequence: NG_009240.2; position 446 of the ZRS) variant segregates with all PPD I–affected individuals. The knockin mouse with this ZRS variant exhibited PPD I phenotype accompanying ectopic and excess expression of Shh. We confirmed that HnRNP K can bind the ZRS and SHH promoters. The ZRS mutant enhanced the binding affinity for HnRNP K and upregulated SHH expression.

Conclusion

Our results identify the first PPD I disease-causing variant. The variant leading to PPD I may be associated with enhancing SHH expression mediated by HnRNP K. This study adds to the ZRS-associated syndromes classification system for PPD and clarifies the underlying molecular mechanisms.

Thumb duplication: molecular analysis of different clinical types

PURPOSE

Molecular analysis of different types of thumb duplication and identification of new suspected gene mutations.

MATERIALS AND METHODS

In a series of patients operated for polydactyly, DNA was extracted from blood samples collected preoperatively. Among these, the samples of two patients with thumb duplication (Wassel types III and IV) were initially selected for molecular analysis. The method of Clinical Exome Solution was used for the study of the phenotype-involved genes. Next-generation sequencing (NGS) was performed on a NextSeq-500 Platform (Illumina), and Sophia DDM^® SaaS algorithms were used for the bioinformatics analysis of the data.

RESULTS

In total, 8-including 4 new-mutations were detected in CEP290 (1 mutation), RPGRIP1 (2 mutations), TMEM216 (2 mutations), FBN1 (1 mutation), CEP164 (1 mutation), and MEGF8 (1 mutation) genes. NGS revealed 3 mutated genes in the patient with Wassel III thumb duplication and 5 mutated genes in the patient with Wassel IV duplication. The molecular analysis revealed that the patients had 2 mutated genes in common, but they only shared one common mutation.

CONCLUSION

The new detected mutations are most probably associated with thumb duplication, as they belong to genes with already described mutations causing ciliopathies, often including polydactyly in their phenotype. Recognition of these mutations will be helpful to prenatal diagnosis, operative treatment strategy prediction, and possible future experimental applications in gene therapy.

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.