Intrafamilial variability of the triphalangeal thumb phenotype in a Dutch population: Evidence for phenotypic progression over generations?

Neglected bilateral triphalangeal of the thumb delta type in adult case: A case report

INTRODUCTION

In rare case, thumb has extra phalanges known as triphalangeal of the thumb (TPT). Patients with TPT can have difficulty doing work/activities that require high precision. Therefore, surgical intervention is essential. This report provides an approach for a patient with TPT.

PRESENTATION OF CASE

A patient with TPT who underwent removal of extra phalanges and arthrodesis of interphalangeal (IP) joints is presented. The left thumb deviated 25o to ulnar while the contralateral part deviated 15o to radial. X-ray revealed both thumbs had extra delta-shaped middle phalanges. Complete excision of extra phalanges and simple arthrodesis of IP joints with two K-wires in 10° to 15° flexion was performed. Healing process ended without any complications and the patient had an improvement.

DISCUSSION

Productive-age patients with TPT can have difficulty doing work and activities that require high precision, especially in the non-opposable type of the right hand. Furthermore, the female patient is highly emphasizing the cosmetics of her hand to increase her self-confidence. Therefore, surgical intervention is essential for this patient. We performed complete excision of extra phalanges and simple arthrodesis of IP joints with two K-wires in 10° to 20° flexion. The first K-wire is introduced intramedullary as a primary fixator for longitudinal alignment, and the second wire is inserted obliquely as an anti-rotation wire. Functional outcome was assessed after 6 months post-removal of the wire which gave a satisfying result.

CONCLUSION

TPT is a rare anomaly which surgical intervention can improve the appearance and the precision of the hand.

A 300-kb microduplication of 7q36.3 in a patient with triphalangeal thumb-polysyndactyly syndrome combined with congenital heart disease and optic disc coloboma: a case report

Background

Triphalangeal thumb-polysyndactyly syndrome (TPT-PS) is a rare well-defined autosomal dominant disorder characterized by long thumbs with three phalanges combined with pre- and postaxial polydactyly/syndactyly of limbs. By now, the syndrome has been reported in several large families from different ethnic backgrounds, with a high degree of inter- and intrafamilial variability. The genome locus responsible for TPT-PS has been mapped to the 7q36.3 region harboring a long-range sonic hedgehog (SHH) regulatory sequence (ZRS). Both single-nucleotide variants and complete duplications of ZRS were shown to cause TPT-PS and similar limb phenotypes. TPT-PS usually forms as isolated limb pathology not associated with additional malformations, in particular, with cardiovascular abnormalities.

Case presentation

Here we report on a rare Russian neonatal case of TPT-PS combined with severe congenital heart disease, namely double outlet right ventricle, and microphthalmia with optic disc coloboma. Pedigree analysis revealed TPT-PS of various expressivity in 10 family members throughout five generations, while the cardiac defect and the eye pathology were detected only in the proband. To extend the knowledge on genotype–phenotype spectrum of TPT-PS, the careful clinical and genomic analysis of the family was performed. High-resolution array-based comparative genomic hybridization (array-CGH) revealed a ~ 300 kb microduplication of 7q36.3 locus (arr[GRCh37] 7q36.3(156385810_156684811) × 3) that co-segregated with TPT-PS in the proband and her mother. The duplication encompassed three genes including LMBR1, the intron 5 of which is known to harbor ZRS. Based on whole-exome sequencing data, no additional pathogenic mutations or variants of uncertain clinical significance were found in morbid cardiac genes or genes associated with a microphthalmia/anophthalmia/coloboma spectrum of ocular malformations.

Conclusions

The results support the previous data, indicating that complete ZRS duplication underlies TPT-PS, and suggest a broader phenotypic impact of the 7q36.3 microduplication. Potential involvement of the 7q36.3 microduplication in the patient’s cardiac and eye malformations is discussed. However, the contribution of some additional genetic/epigenetic factors to the complex patient`s phenotype cannot be excluded entirely. Further comprehensive functional studies are needed to prove the possible involvement of the 7q36.3 locus in congenital heart disease and eye pathology.

Variable expression of subclinical phenotypes instead of reduced penetrance in families with mild triphalangeal thumb phenotypes

Background

The of zone of polarizing activity regulatory sequence (ZRS) is a regulatory element residing in intron 5 of LMBR1 and regulates Sonic Hedgehog expression in the limb bud. Variants in the ZRS are generally fully penetrant and can cause triphalangeal thumb (TPT) and polydactyly in affected families.

Objective

In this report, we describe two families with mild phenotypical presentation.

Methods

We performed a field study for clinical evaluation and sequenced the ZRS for variantsusing Sanger sequencing.

Results

In family I, a novel 165A>G variant in the ZRS (g.156584405A>G, GRCh37/Hg19) was found. In family II, we identified a 295T>C variant in the ZRS (g.156584535T>C, GRCh37/Hg19). Family members of both families who were presumed to be unaffected shared the variant in the ZRS with affected family members, suggesting reduced penetrance of the genotype. However, clinical examination of these unaffected family members revealed minor anomalies like broad thumbs and lack of thumb opposition. As the phenotype in affected patients is remarkably mild, we suggest that these ZRS variants are minimally disruptive for Sonic Hedgehog expression and therefore can result in subclinical phenotypes.

Conclusion

Our study underlines the importance of accurate clinical examination and appropriate genetic counselling in families with mild cases of TPT.

Comprehensive In Vivo Interrogation Reveals Phenotypic Impact of Human Enhancer Variants

Establishing causal links between non-coding variants and human phenotypes is an increasing challenge. Here, we introduce a high-throughput mouse reporter assay for assessing the pathogenic potential of human enhancer variants in vivo and examine nearly a thousand variants in an enhancer repeatedly linked to polydactyly. We show that 71% of all rare non-coding variants previously proposed as causal lead to reporter gene expression in a pattern consistent with their pathogenic role. Variants observed to alter enhancer activity were further confirmed to cause polydactyly in knockin mice. We also used combinatorial and single-nucleotide mutagenesis to evaluate the in vivo impact of mutations affecting all positions of the enhancer and identified additional functional substitutions, including potentially pathogenic variants hitherto not observed in humans. Our results uncover the functional consequences of hundreds of mutations in a phenotype-associated enhancer and establish a widely applicable strategy for systematic in vivo evaluation of human enhancer variants.

A multidisciplinary review of triphalangeal thumb

Despite being a rare congenital limb anomaly, triphalangeal thumb is a subject of research in various scientific fields, providing new insights in clinical research and evolutionary biology. The findings of triphalangeal thumb can be predictive for other congenital anomalies as part of an underlying syndrome. Furthermore, triphalangeal thumb is still being used as a model in molecular genetics to study gene regulation by long-range regulatory elements. We present a review that summarizes a number of scientifically relevant topics that involve the triphalangeal thumb phenotype. Future initiatives involving multidisciplinary teams collaborating in the field of triphalangeal thumb research can lead to a better understanding of the pathogenesis and molecular mechanisms of this condition as well as other congenital upper limb anomalies.

Classification of congenital upper limb anomalies: towards improved communication, diagnosis, and discovery

Recently the International Federation of Societies for Surgery of the Hand replaced the Swanson scheme for classifying congenital upper limb anomalies with the Oberg, Manske, Tonkin (OMT) classification. This review explores the reasons for this change after nearly 50 years of using the Swanson classification. In particular, it documents the state of our understanding regarding genetics and limb development at the time Swanson generated his classification. It also describes the continued progress in clinical genetics and developmental biology. Such progress drives the need to embrace and incorporate these changes within a new classification scheme; one that will improve communication, diagnosis, and support further discovery of the pathogenesis of congenital hand anomalies.

Triphalangeal thumb: clinical features and treatment

Triphalangeal thumb is a rare congenital anomaly in which the thumb has three phalanges. Clinical presentation of triphalangeal thumb can vary considerably and can be present in both hands or unilateral. The thumb can be long with a finger-like appearance. The presence of clinodactyly depends on the shape of the extra phalanx varying from wedge-shaped to rectangular. Various joints, ligaments, muscles, and tendons of the first ray can be hypoplastic or absent, with varying degrees of stiffness or instability. The aim of surgical treatment is to reconstruct or correct the anatomic anomalies to obtain greater function and a more acceptable appearance. In our series, operations varied from removal of the delta phalanx with ligament reconstruction to multiple osteotomies and rebalancing of soft tissues. Results in these often complex cases can be rewarding if the surgeon has sufficient knowledge of the underlying anatomic differences. This review summarizes our current concepts of presentation and management of the triphalangeal thumb.

Documenting Combined Congenital Upper Limb Anomalies Using the Oberg, Manske, and Tonkin Classification: Implications for Epidemiological Research and Outcome Comparisons

PURPOSE

Congenital upper limb anomalies (CULAs) exhibit a wide spectrum of phenotypic manifestations. To help the clinician evaluating this variety of CULAs, the Oberg, Manske, and Tonkin (OMT) classification was recently introduced. The OMT classification allows for documentation of combined hand anomalies. However, subsequent epidemiological and validation studies using the OMT scheme commonly registered only the main anomaly per arm. This study illustrates both the deficits of single diagnosis documentation as well as the merits of registering every anomaly for epidemiological research, outcome comparison, and overall applicability of the classification.

METHODS

We retrospectively reviewed patients visiting the Erasmus MC - Sophia Children's Hospital between 2012 and 2014. All congenital anomalies of both limbs were classified according to the OMT scheme. The frequency of combined diagnoses as well as recurrent combinations were analyzed. The relation to the coregistered syndromes was studied.

RESULTS

We included 746 patients, 79.5% of whom could be documented with a single OMT diagnosis. In 20.5%, a combination of OMT diagnoses was documented. We documented 149 different combinations: 102 were documented once, 47 were documented repeatedly (n = 196); for example, in patients with Greig syndrome. The prevalence of this syndrome was significantly higher in patients with a combination of radial polydactyly, ulnar polydactyly, and/or syndactyly (2.9% vs 33.3% and 60% in patients with 1 vs 2 and 3 diagnoses).

CONCLUSIONS

Documentation of combined OMT diagnoses is required in a fifth of the patients. Not doing so will cause loss of phenotypic information and can hamper outcome comparison and epidemiological research. Documentation of combined OMT diagnoses can help to identify subgroups within a population, for example, patients with an underlying syndrome. Last, combined documentation of diagnoses improves flexibility of the classification and thereby better allows universal application.

CLINICAL RELEVANCE

Consensus on the application of the OMT classification is critical to achieving the universal adoption of the system by hand surgeons and other medical professionals.

A point mutation in the pre-ZRS disrupts sonic hedgehog expression in the limb bud and results in triphalangeal thumb-polysyndactyly syndrome

PURPOSE

The zone of polarizing activity regulatory sequence (ZRS) is an enhancer that regulates sonic hedgehog during embryonic limb development. Recently, mutations in a noncoding evolutionary conserved sequence 500 bp upstream of the ZRS, termed the pre-ZRS (pZRS), have been associated with polydactyly in dogs and humans. Here, we report the first case of triphalangeal thumb-polysyndactyly syndrome (TPT-PS) to be associated with mutations in this region and show via mouse enhancer assays how this mutation leads to ectopic expression throughout the developing limb bud.

METHODS

We used linkage analysis, whole-exome sequencing, Sanger sequencing, fluorescence in situ hybridization, multiplex ligation-dependent probe amplification, single-nucleotide polymorphism array, and a mouse transgenic enhancer assay.

RESULTS

Ten members of a TPT-PS family were included in this study. The mutation was linked to chromosome 7q36 (LOD score 3.0). No aberrations in the ZRS could be identified. A point mutation in the pZRS (chr7:156585476G>C; GRCh37/hg19) was detected in all affected family members. Functional characterization using a mouse transgenic enhancer essay showed extended ectopic expression dispersed throughout the entire limb bud (E11.5).

CONCLUSION

Our work describes the first mutation in the pZRS to be associated with TPT-PS and provides functional evidence that this mutation leads to ectopic expression of this enhancer within the developing limb.

Intrafamilial variability of the triphalangeal thumb phenotype in a Dutch population: Evidence for phenotypic progression over generations?

Triphalangeal thumbs (TPTs) are regularly caused by mutations in the ZRS in LMBR1. Phenotypic variability can be present in TPT‐families. However, recent observations suggest an increased occurrence of severe phenotypes in the Dutch TPT‐population. Therefore, the aim of this study is to investigate the progression of the clinical severity of TPT‐phenotype through generations. Index patients from a Dutch TPT‐population were identified. A 105C>G mutation in the ZRS has previously been confirmed in this population. Questionnaires regarding family occurrence and phenotypes were distributed. Subsequently, families were visited to validate the phenotype. Both occurrence and inheritance patterns of the TPT‐phenotype were analyzed through multiple generations. One hundred seventy patients with TPT were identified from 11 families. When considering all 132 segregations (parent‐to‐child transmission), 54% of the segregations produced a stable phenotype, 38% produced a more severe phenotype while only 8% of the phenotype was less severe when compared to the affected parents. Overall, 71% of the index patients had a more severe phenotype compared to their great‐grandparent. Although all family members share an identical mutation in the ZRS (105C>G), it does not explain the wide phenotypic range of anomalies. Our observational study provides better estimations for counseling and provides new insights in the long‐range regulation of SHH by the ZRS‐enhancer. In the current study, we provide evidence that the assumed variability in TPT‐phenotype is not random, but in fact it is more likely that the expression becomes more severe in the next generation. Therefore, we observe a pattern that resembles phenotypic anticipation in TPT‐families.