New mesomelic dysplasia with absent fibulae and triangular tibiae

Variants in the degron of AFF3 are associated with intellectual disability, mesomelic dysplasia, horseshoe kidney, and epileptic encephalopathy

The ALF transcription factor paralogs, AFF1, AFF2, AFF3, and AFF4, are components of the transcriptional super elongation complex that regulates expression of genes involved in neurogenesis and development. We describe an autosomal dominant disorder associated with de novo missense variants in the degron of AFF3, a nine amino acid sequence important for its binding to ubiquitin ligase, or with de novo deletions of this region. The sixteen affected individuals we identified, along with two previously reported individuals, present with a recognizable pattern of anomalies, which we named KINSSHIP syndrome (KI for horseshoe kidney, NS for Nievergelt/Savarirayan type of mesomelic dysplasia, S for seizures, H for hypertrichosis, I for intellectual disability, and P for pulmonary involvement), partially overlapping the AFF4-associated CHOPS syndrome. Whereas homozygous Aff3 knockout mice display skeletal anomalies, kidney defects, brain malformations, and neurological anomalies, knockin animals modeling one of the microdeletions and the most common of the missense variants identified in affected individuals presented with lower mesomelic limb deformities like KINSSHIP-affected individuals and early lethality, respectively. Overexpression of AFF3 in zebrafish resulted in body axis anomalies, providing some support for the pathological effect of increased amount of AFF3. The only partial phenotypic overlap of AFF3- and AFF4-associated syndromes and the previously published transcriptome analyses of ALF transcription factors suggest that these factors are not redundant and each contributes uniquely to proper development.

De novo AFF3 variant in a patient with mesomelic dysplasia with foot malformation

Mesomelic dysplasia (MD) encompasses a heterogeneous group of disorders characterized by shortening of the middle segments of the limbs. Previous studies have revealed the development of Nievergelt type-like MD accompanied by postaxial toe reduction in a patient with a ~500 kb microdeletion at 2q11.2 involving AFF3 alone, and the occurrence of Nievergelt type-like MD in mice with a ~353 kb deletion involving Aff3, together with strong expression of mouse Aff3 in the developing limbs and zeugopod. We encountered a 2 6/12-year-old Japanese girl with an unclassifiable MD associated with hypoplasia of postaxial toes, and identified a de novo likely pathogenic variant of AFF3 (NM_002285.2:c.697 G > A, p.(Ala233Thr)) by whole exome sequencing. The results provide further evidence for AFF3 being the causative gene for MD with foot malformation which may be termed "AFF3-related MD" or "Steichen-Gersdorf type MD".

Concomitant rhomboid-shaped tibiae and fibulae, finger-like projections, and orthopedic management in a new variant of nievergelt syndrome: A case report

INTRODUCTION

The rare Nievergelt syndrome (NS) is the most severe form of mesomelic dysplasia and is characterized by disproportionate shortness of the limbs. The aim of this case report was to describe the clinical and radiological features of a rare case of NS.

PRESENTATION OF CASE

Here we describe a female patient originally presenting with bilateral hand, lower leg, and foot deformities at the age of 10 years old. In addition to the characteristic features of NS, this patient presented with finger-like projections on her heels, bilateral hand anomalies, and atypical facial features. She underwent concomitant bilateral tibial lengthening and deformity correction using external fixators due to severe bilateral lower leg deformities with shortness. At 10 years of age, this patient was able to walk independently with significant improvement in her ambulation.

DISCUSSION

There is a clear gap in the literature regarding the orthopedic management of mesomelic limb deformities due to NS. No studies have been designed to illustrate surgical planning in the management of orthopedic deformities in this rare syndrome.

CONCLUSION

Limb lengthening and deformity correction using an external fixator can be considered as a salvage method or alternative to amputation for patients with severe mesomelic limb deformities due to NS.

A case of mesomelic dysplasia Kantaputra type--new findings and a new diagnostic approach

Mesomelic dysplasia is a heterogeneous group of rare bone diseases characterized by disproportionate shortness of middle segments of limbs and short stature. This study reports a male patient with an early diagnosed mesomelic dysplasia Kantaputra type (MIM*156232), characterized by symmetric, bilateral forearm and lower leg shortening with feet malformations and ankle-tarsal synostoses. As a result of several diagnostic biases in defining the mesomelic syndromes, we attempted to categorize symptoms and to clarify hitherto difficult discrimination between mesomeliae. Given that specific ankle joint alignment distortions seem to be pathognomonic for Kantaputra type (especially a fibulo-calcanear and, to a lesser extent, a tibio-talar synostosis), but not detectable with plane radiography, we encouraged use of MRI evaluation as an indispensable modality for proper diagnosis and further preoperative planning.

Triangular tibia with fibular aplasia associated with a microdeletion on 2q11.2 encompassing LAF4

Nievergelt syndrome (NS) is an autosomal dominant mesomelic dysplasia characterized by specific deformities of the radius, ulna, fibula and a rhomboid shape of the tibia. Phenotypically overlapping conditions such as mesomelic dysplasia, Savarirayan-type (MIM 605274), have been described, but their pathogenesis also remains unknown. We report on a girl with fibular agenesis, severely abnormal, triangular tibiae, urogenital tract malformations, failure to thrive, convulsions and recurrent apnoeas leading to respiratory arrest at the age of 4 months. Her skeletal findings correspond to those of the mesomelic dysplasia, Savarirayan-type recently described in two patients. In addition to the skeletal findings, our patient had central nervous system manifestations and developmental anomalies of the urogenital tract. In the patient described in this study, array comparative genomic hybridization (CGH) analysis revealed a de novo interstitial microdeletion of 500 kb on chromosome 2q11.1 containing the LAF4/AFF3 (lymphoid-nuclear-protein-related AF4) gene. In situ hybridization analysis of Laf4 in mouse embryos revealed expression in the developing brain, in the limb buds and in the zeugopod corresponding to the limb phenotype. Haploinsufficiency for LAF4/AFF3 is associated with limb, brain and urogenital malformations and specific changes of the tibia that are part of the NS spectrum.

Spondylo-mega-epiphyseal dysplasia with prominent upper limb mesomelia, punctate calcifications, and deafness

We report on a previously undescribed form of skeletal dysplasia with rhizomelic, acromelic, and prominent mesomelic shortening, distal ulnar epiphyseal and pubic punctate calcifications (stippling), mega-epiphyses, platyspondyly, anterior beaking of the vertebrae, and sensorineural hearing loss. We compare this case to the other reported forms of skeletal dysplasias, particularly the mesomelic, acromesomelic, and mega-epiphyseal disorders.

International nosology and classification of constitutional disorders of bone (2001)

The last International Classification of Constitutional Disorders of Bone was published in 1998. Since then rapid advances have been made in identifying the molecular changes responsible for defined conditions and new disorders are constantly being delineated. For these reasons a further update on the classification is appropriate. It has been expended to not only the osteochondrodysplasias (33 groups) but also genetically determined dysostoses (3 groups).

A t(2;8) balanced translocation with breakpoints near the human HOXD complex causes mesomelic dysplasia and vertebral defects

Mesomelic dysplasia is a severe shortening of forearms and forelegs, and is found in several distinct human syndromes. Here, we report the cloning of the breakpoints of a human t(2;8)(q31;p21) balanced translocation associated with mesomelic dysplasia of the upper limbs, as well as with vertebral defects. We show that this translocation does not disrupt any gene, hence it most likely exerts its deleterious effect by modifying gene regulation. The HOXD complex lies approximately 60 kb from the translocation breakpoint on chromosome 2. This cluster of genes has an important role in the development of both the vertebral column and the limbs. Only a few cases of mutations of these homeotic genes have been described so far in humans. However, gain- and loss-of-function of Hoxd genes in mice can induce mesomelic dysplasia-like phenotypes, suggesting that misexpression of HOXD genes may indeed be at the origin of this hereditary phenotype.