Evolution of clinical and radiological presentations of spondyloepimetaphyseal dysplasia, RPL13-related: Description of 11 further cases.

Spondyloepimetaphyseal dysplasia (SEMD), RPL13-related is caused by heterozygous variants in RPL13, which encodes the ribosomal protein eL13, a component of the 60S human ribosomal subunit. Here, we describe the clinical and radiological evolution of 11 individuals, 7 children and 4 adults, from 6 families. Some of the skeletal features improved during the course of this condition, whilst others worsened. We describe for the first time "corner fractures" as a feature of this dysplasia which as with other dysplasias disappear with age. In addition, we review the heights and skeletal anomalies of these reported here and previously in a total of 25 individuals from 15 families. In this study, six different RPL13 variants were identified, five of which were novel. All were located in the apparently hotspot region, located in intron 5 and exon 6. Splicing assays were performed for two of the three previously undescribed splicing variants. Until now, all splice variants have occurred in the intron 5 splice donor site, incorporating an additional 18 amino acids to the mutant protein. Here, we report the first variant in intron 5 splice acceptor site which generates two aberrant transcripts, deleting the first three and four amino acids encoded by exon 6. Thus, this study doubles the number of SEMD-RPL13-related cases and variants reported to date and describes unreported age-related clinical and radiological features.

Biallelic cGMP-dependent type II protein kinase gene (PRKG2) variants cause a novel acromesomelic dysplasia.

BACKGROUND: C-type natriuretic peptide (CNP), its endogenous receptor, natriuretic peptide receptor-B (NPR-B), as well as its downstream mediator, cyclic guanosine monophosphate (cGMP) dependent protein kinase II (cGKII), have been shown to play a pivotal role in chondrogenic differentiation and endochondral bone growth. In humans, biallelic variants in NPR2, encoding NPR-B, cause acromesomelic dysplasia, type Maroteaux, while heterozygous variants in NPR2 (natriuretic peptide receptor 2) and NPPC (natriuretic peptide precursor C), encoding CNP, cause milder phenotypes. In contrast, no variants in cGKII, encoded by the protein kinase cGMP-dependent type II gene (PRKG2), have been reported in humans to date, although its role in longitudinal growth has been clearly demonstrated in several animal models. METHODS: Exome sequencing was performed in two girls with severe short stature due to acromesomelic limb shortening, brachydactyly, mild to moderate platyspondyly and progressively increasing metaphyseal alterations of the long bones. Functional characterisation was undertaken for the identified variants. RESULTS: Two homozygous PRKG2 variants, a nonsense and a frameshift, were identified. The mutant transcripts are exposed to nonsense-mediated decay and the truncated mutant cGKII proteins, partially or completely lacking the kinase domain, alter the downstream mitogen activation protein kinase signalling pathway by failing to phosphorylate c-Raf 1 at Ser43 and subsequently reduce ERK1/2 activation in response to fibroblast growth factor 2. They also downregulate COL10A1 and upregulate COL2A1 expression through SOX9. CONCLUSION: In conclusion, we have clinically and molecularly characterised a new acromesomelic dysplasia, acromesomelic dysplasia, PRKG2 type (AMDP).

Identification of the third FGF9 variant in a girl with multiple synostosis-comparison of the genotype:phenotype of FGF9 variants in humans and mice.

Multiple synostosis syndrome (SYNS) is a heterogeneous group of genetic disorders mainly characterized by multiple joint synostosis due to variants in either NOG, GDF5, FGF9 or GDF6. To date, only two FGF9 variants have been associated with SYNS, characterized with hand and feet joint synostosis and fusion of the elbow and vertebral lumbar joints. Craniosynostosis was also observed in one family. Here, we report the clinical and radiological description of a young girl with a third heterozygous FGF9 variant, NM_002010.2:c.427A>T;p.(Asn143Tyr), which interestingly, is located at the same amino acid as the well characterized spontaneous Eks mouse variant. We also compare the genotype: phenotypes observed between humans and mice with SYNS.

Heterozygous aggrecan variants are associated with short stature and brachydactyly: Description of 16 probands and a review of the literature.

OBJECTIVE: Mutations in the aggrecan gene (ACAN) have been identified in two autosomal dominant skeletal dysplasias, spondyloepiphyseal dysplasia, Kimberley type (SEDK), and osteochondritis dissecans, as well as in a severe recessive dysplasia, spondyloepimetaphyseal dysplasia, aggrecan type. Next-generation sequencing (NGS) has aided the identification of heterozygous ACAN mutations in individuals with short stature, minor skeletal defects and mild facial dysmorphisms, some of whom have advanced bone age (BA), poor pubertal spurt and early growth cessation as well as precocious osteoarthritis. DESIGN AND METHODS: This study involves clinical and genetic characterization of 16 probands with heterozygous ACAN variants, 14 with short stature and mild skeletal defects (group 1) and two with SEDK (group 2). Subsequently, we reviewed the literature to determine the frequency of the different clinical characteristics in ACAN-positive individuals. RESULTS: A total of 16 ACAN variants were located throughout the gene, six pathogenic mutations and 10 variants of unknown significance (VUS). Interestingly, brachydactyly was observed in all probands. Probands from group 1 with a pathogenic mutation tended to be shorter, and 60% had an advanced BA compared to 0% in those with a VUS. A higher incidence of coxa valga was observed in individuals with a VUS (37% vs 0%). Nevertheless, other features were present at similar frequencies. CONCLUSIONS: ACAN should be considered as a candidate gene in patients with short stature and minor skeletal defects, particularly those with brachydactyly, and in patients with spondyloepiphyseal dysplasia. It is also important to note that advanced BA and osteoarticular complications are not obligatory conditions for aggrecanopathies/aggrecan-associated dysplasias.

Two novel POC1A mutations in the primordial dwarfism, SOFT syndrome: Clinical homogeneity but also unreported malformations.

Primordial dwarfism encompasses rare conditions characterized by severe intrauterine growth retardation and growth deficiency throughout life. Recently, three POC1A mutations have been reported in six families with the primordial dwarfism, SOFT syndrome (Short stature, Onychodysplasia, Facial dysmorphism, and hypoTrichosis). Using a custom-designed Next-generation sequencing skeletal dysplasia panel, we have identified two novel homozygous POC1A mutations in two individuals with primordial dwarfism. The severe growth retardation and the facial profiles are strikingly similar between our patients and those described previously. However, one of our patients was diagnosed with severe foramen magnum stenosis and subglottic tracheal stenosis, malformations not previously associated with this syndrome. Our findings confirm that POC1A mutations cause SOFT syndrome and that mutations in this gene should be considered in patients with severe pre- and postnatal short stature, symmetric shortening of long bones, triangular facies, sparse hair and short, thickened distal phalanges.

Variants in both the N- or C-terminal domains of IHH lead to defective secretion causing short stature and skeletal defects.

BACKGROUND: Heterozygous Indian Hedgehog gene (IHH) variants are associated with brachydactyly type A1 (BDA1). However, in recent years, numerous variants have been identified in patients with short stature and more variable forms of brachydactyly. Many are located in the C-terminal domain of IHH (IHH-C), which lacks signaling activity but is critical for auto-cleavage and activation of the N-terminal (IHH-N) peptide. The absence of functional studies of IHH variants, particularly for those located in IHH-C, has led to these variants being classified as variants of uncertain significance (VUS). OBJECTIVE: To establish a simple functional assay to determine the pathogenicity of IHH VUS and confirm that variants in the C-terminal domain affect protein function. DESIGN/METHODS: In vitro studies were performed for 9 IHH heterozygous variants, to test their effect on secretion and IHH intracellular processing by western blot of cells expressing each variant. RESULTS: IHH secretion was significantly reduced in all mutants, regardless of the location. Similarly, intracellular levels of N-terminal and C-terminal IHH peptides were severely reduced in comparison with the control. Two variants present at a relatively high frequency in the general population also reduced secretion but to a lesser degree in the heterozygous state. CONCLUSIONS: These studies provide the first evidence that variants in the C-terminal domain affect the secretion capacity of IHH and thus, reduce availability of IHH ligand, resulting in short stature and mild skeletal defects. The secretion assay permits a relatively easy test to determine the pathogenicity of IHH variants. All studied variants affected secretion and interestingly, more frequent population variants appear to have a deleterious effect and thus contribute to height variation.

High prevalence of variants in skeletal dysplasia associated genes in individuals with short stature and minor skeletal anomalies.

OBJECTIVE: Next generation sequencing (NGS) has expanded the diagnostic paradigm turning the focus to the growth plate. The aim of the study was to determine the prevalence of variants in genes implicated in skeletal dysplasias in probands with short stature and mild skeletal anomalies. DESIGN: Clinical and radiological data were collected from 108 probands with short stature and mild skeletal anomalies. METHODS: A customized skeletal dysplasia NGS panel was performed. Variants were classified using ACMG recommendations and Sherloc. Anthropometric measurements and skeletal anomalies were subsequently compared in those with or without an identified genetic defect. RESULTS: Heterozygous variants were identified in 21/108 probands (19.4%). Variants were most frequently identified in ACAN (n = 10) and IHH (n = 7) whilst one variant was detected in COL2A1, CREBBP, EXT1, and PTPN11. Statistically significant differences (P < 0.05) were observed for sitting height/height (SH/H) ratio, SH/H ratio standard deviation score (SDS), and the SH/H ratio SDS >1 in those with an identified variant compared to those without. CONCLUSIONS: A molecular defect was elucidated in a fifth of patients. Thus, the prevalence of mild forms of skeletal dysplasias is relatively high in individuals with short stature and mild skeletal anomalies, with variants in ACAN and IHH accounting for 81% of the cases. An elevated SH/H ratio appears to be associated with a greater probability in detecting a variant, but no other clinical or radiological feature has been found determinant to finding a genetic cause. Currently, we cannot perform extensive molecular studies in all short stature individuals so detailed clinical and radiological phenotyping may orientate which are the candidate patients to obtain worthwhile results. In addition, detailed phenotyping of probands and family members will often aid variant classification.

Clinical and Molecular Description of 16 Families With Heterozygous IHH Variants.

CONTEXT: Heterozygous variants in the Indian hedgehog gene (IHH) have been reported to cause brachydactyly type A1 and mild hand and feet skeletal anomalies with short stature. Genetic screening in individuals with short stature and mild skeletal anomalies has been increasing over recent years, allowing us to broaden the clinical spectrum of skeletal dysplasias. OBJECTIVE: The objective of this article is to describe the genotype and phenotype of 16 probands with heterozygous variants in IHH. PATIENTS AND METHODS: Targeted next-generation sequencing or Sanger sequencing was performed in patients with short stature and/or brachydactyly for which the genetic cause was unknown. RESULTS: Fifteen different heterozygous IHH variants were detected, one of which is the first reported complete deletion of IHH. None of the patients showed the classical phenotype of brachydactyly type A1. The most frequently observed clinical characteristics were mild to moderate short stature as well as shortening of the middle phalanx on the fifth finger. The identified IHH variants were demonstrated to cosegregate with the short stature and/or brachydactyly in the 13 probands whose family members were available. However, clinical heterogeneity was observed: Two short-statured probands showed no hand radiological anomalies, whereas another 5 were of normal height but had brachydactyly. CONCLUSIONS: Short stature and/or mild skeletal hand defects can be caused by IHH variants. Defects in this gene should be considered in individuals with these findings, especially when there is an autosomal dominant pattern of inheritance. Although no genotype-phenotype correlation was observed, cosegregation studies should be performed and where possible functional characterization before concluding that a variant is causative.

IHH Gene Mutations Causing Short Stature With Nonspecific Skeletal Abnormalities and Response to Growth Hormone Therapy.

Context: Genetic evaluation has been recognized as an important tool to elucidate the causes of growth disorders. Objective: To investigate the cause of short stature and to determine the phenotype of patients with IHH mutations, including the response to recombinant human growth hormone (rhGH) therapy. Patients and Methods: We studied 17 families with autosomal-dominant short stature by using whole exome sequencing and screened IHH defects in 290 patients with growth disorders. Molecular analyses were performed to evaluate the potential impact of N-terminal IHH variants. Results: We identified 10 pathogenic or possibly pathogenic variants in IHH, an important regulator of endochondral ossification. Molecular analyses revealed a smaller potential energy of mutated IHH molecules. The allele frequency of rare, predicted to be deleterious IHH variants found in short-stature samples (1.6%) was higher than that observed in two control cohorts (0.017% and 0.08%; P < 0.001). Identified IHH variants segregate with short stature in a dominant inheritance pattern. Affected individuals typically manifest mild disproportional short stature with a frequent finding of shortening of the middle phalanx of the fifth finger. None of them have classic features of brachydactyly type A1, which was previously associated with IHH mutations. Five patients heterozygous for IHH variants had a good response to rhGH therapy. The mean change in height standard deviation score in 1 year was 0.6. Conclusion: Our study demonstrated the association of pathogenic variants in IHH with short stature with nonspecific skeletal abnormalities and established a frequent cause of growth disorder, with a preliminary good response to rhGH.