Embryology of familial (non-syndromic) brachydactyly of the hand

Genetics, Clinical Presentation, Radiological Features, and Midterm Outcome of Closing Wedge Osteotomy in Children With Brachydactyly Type C

BACKGROUND

Brachydactyly (BD) type C is a rare form of familial BD caused by GDF5 mutations. Some of the affected children have severe clinodactyly requiring surgery. The literature is limited to case reports.

PATIENTS AND METHODS

The current retrospective study included 15 Saudi Arabian families with 42 affected children seen by the author for 25 years. A total of 23 digits (in 23 hands) underwent surgical correction of clinodactyly using a closing wedge osteotomy. The current study reports on the genetics, clinical presentation, radiological features, and midterm outcome of surgery.

RESULTS

Genetic analysis was done in 6 families and confirmed the presence of 2 novel missense mutations (p.Met173Val in 3 families and p.Thr203Asn in 3 families) in the GDF5 gene. All cases in the study group demonstrated the classical clinical and radiographic features of BD type C. However, only 1 hand showed all the features of angel-shaped bony defect. The clinodactyly defect was mostly observed in the index or middle fingers. Surgery for the clinodactyly defect was only done if there was finger overlap. Closing wedge osteotomy was done in a total of 23 digits with a satisfactory outcome.

CONCLUSIONS

This study represents the largest reported series of children undergoing surgery for correction of BD type C clinodactyly with a uniform technique performed by a single surgeon. The closing wedge osteotomy used resulted in good midterm outcomes, although long-term follow-up is lacking.

GDF5 mutation case report and a systematic review of molecular and clinical spectrum: Expanding current knowledge on genotype-phenotype correlations

INTRODUCTION

Brachydactyly is a bone development abnormality presenting with variable phenotypes and different transmission patterns. Mutations in GDF5 (Growth and Differentiation Factor 5, MIM *601146) account for a significant amount of cases. Here, we report on a three-generation family, where the proband and the grandfather have an isolated brachydactyly with features of both type A1 (MIM #112500) and type C (MIM #113100), while the mother shows only subtle hand phenotype signs.

MATERIALS AND METHODS

Whole Exome Sequencing (WES) was performed on the two affected individuals. An in-depth analysis of GDF5 genotype-phenotype correlations was performed through literature reviewing and retrieving information from several databases to elucidate GDF5-related molecular pathogenic mechanisms.

RESULTS

WES analysis disclosed a pathogenic variant in GDF5 (NM_000557.5:c.157dup; NP_000548.2:p.Leu53Profs*41; rs778834209), segregating with the phenotype. The frameshift variant was previously associated with Brachydactyly type C (MIM #113100), in heterozygosity, and with the severe Grebe type chondrodysplasia (MIM #200700), in homozygosity. In-depth analysis of literature and databases allowed to retrieve GDF5 mutations and correlations to phenotypes. We disclosed the association of 49 GDF5 pathogenic mutations with eight phenotypes, with both autosomal dominant and recessive transmission patterns. Clinical presentations ranged from severe defects of limb morphogenesis to mild redundant ossification. We suggest that such clinical gradient can be linked to a continuum of GDF5-activity variation, with loss of GDF5 activity underlying bone development defects, and gain of function causing disorders with excessive bone formation.

CONCLUSIONS

Our analysis of GDF5 pathogenicity mechanisms furtherly supports that mutation and zygosity backgrounds resulting in the same level of GDF5 activity may lead to similar phenotypes. This information can aid in interpreting the potential pathogenic effect of new variants and in supporting an appropriate genetic counseling.

A Review of the Phenotype of Synpolydactyly Type 1 in Homozygous Patients: Defining the Relatively Long and Medially Deviated Big Toe with/without Cupping of the Forefoot as a Pathognomonic Feature in the Phenotype

Synpolydactyly type 1 (SPD1, OMIM 186000) is inherited as autosomal dominant and is caused by HOXD13 mutations. The condition is rare and is known for its phenotypic heterogeneity. In the homozygous state, the phenotype is generally more severe and is characterized by three main features: a more severe degree of syndactyly, a more severe degree of brachydactyly, and the frequent loss of the normal tubular shape of the metacarpals/metatarsals. Due to the phenotypic heterogeneity and the phenotypic overlap with other types of syndactyly, no pathognomonic feature has been described for the homozygous phenotype of SPD1. In the current communication, the author reviews the literature on the phenotypes of SPD1 in homozygous patients. The review documents that not all homozygous patients show a severe hand phenotype. The review also defines the “relatively long and medially deviated big toe with/without cupping of the forefoot” as a pathognomonic feature in the phenotype. Illustration of this feature is done through a demonstrative clinical report in a multigeneration family with SPD1 and HOXD13 polyalanine repeat expansion. Finally, the pathogenesis of the clinical features is reviewed.

Genetic regulation of linear growth

Linear growth occurs at the growth plate. Therefore, genetic defects that interfere with the normal function of the growth plate can cause linear growth disorders. Many genetic causes of growth disorders have already been identified in humans. However, recent genome-wide approaches have broadened our knowledge of the mechanisms of linear growth, not only providing novel monogenic causes of growth disorders but also revealing single nucleotide polymorphisms in genes that affect height in the general population. The genes identified as causative of linear growth disorders are heterogeneous, playing a role in various growth-regulating mechanisms including those involving the extracellular matrix, intracellular signaling, paracrine signaling, endocrine signaling, and epigenetic regulation. Understanding the underlying genetic defects in linear growth is important for clinicians and researchers in order to provide proper diagnoses, management, and genetic counseling, as well as to develop better treatment approaches for children with growth disorders.