Clinical variability in DYNC2H1-related skeletal ciliopathies includes Ellis-van Creveld syndrome

Expanding the genetic spectrum of short rib polydactyly syndrome: Novel DYNC2H1 variants and functional insights

INTRODUCTION

Short rib polydactyly syndrome (SRPS), with or without polydactyly, also known as Verma-Naumoff/Saldino-Noonan syndrome, is a type of skeletal ciliopathy. Initially, variants in the IFT80 gene were implicated; however, approximately half of the SRPS cases are associated with variants in the DYNC2H1 gene. Additionally, digenic variants involving DYNC2H1 and NEK1 can contribute to the syndrome.

MATERIALS AND METHODS

This case report describes a male patient presenting with characteristic SRPS features, including a constricted thorax and shortened limbs. Exome sequencing was performed to identify causative variants, followed by functional analyses to assess the pathogenicity of the identified variants, including a synonymous variant.

RESULTS

Exome sequencing identified compound heterozygous variants in the DYNC2H1 gene: a novel missense variant c.6439G>T p.(Asp2147Tyr) and a synonymous variant c.6477G>A p.(Gln2159=). Functional analyses confirmed that the synonymous variant triggers nonsense-mediated decay of the affected allele.

CONCLUSION

This study expands the spectrum of DYNC2H1 variants associated with SRPS and emphasizes the importance of functional analyses in genetic diagnostics. Demonstrating pathogenicity for a synonymous variant highlights the necessity for comprehensive variant assessments to improve diagnostic accuracy and enable early intervention. These findings have significant implications for molecular diagnostics and personalized therapy strategies in skeletal ciliopathies.

Phenotypic heterogeneity in DYNC2H1-related short-rib thoracic dysplasia: antenatal indicators and postnatal outcomes

INTRODUCTION

DYNC2H1-related short-rib thoracic dysplasia with/without polydactyly (SRTD), formerly asphyxiating thoracic dystrophy-Jeune syndrome, is a rare genetic skeletal disorder characterised by a narrow thorax, short ribs, shortened long bones and brachydactyly/polydactyly. DYNC2H1-related SRTD shows significant phenotypic variability. There is limited information regarding correlations between genotypes, antenatal ultrasound findings and clinical phenotypes and severity.

METHODS

A retrospective study of confirmed DYNC2H1-related SRTD cases was conducted through paper and digital medical records. Data collected included patient demographics, initial presentation, postnatal progression, childhood follow-up, antenatal ultrasound imaging, postnatal skeletal surveys and genetic variant analysis.

RESULTS

Nine individuals from eight families across three tertiary genetic centres in England were included in the study. Eight presented in the antenatal period (gestation 14-36 weeks) and one in the postnatal period at 6 weeks. All nine displayed a narrow thorax and eight displayed shortened long bones (humerus and/or femur). Polydactyly was less common and seen in only four individuals. Phenotypic severity was variable, including mild (n=4), moderate requiring respiratory support (n=2) and severe/lethal (n=3) cases. Earlier antenatal presentation and more significant femur shortening and bowing were predictive of poor postnatal prognosis, and there were no clear genotype-phenotype correlations. We also report seven novel DYNC2H1 variants, not previously reported.

CONCLUSION

DYNC2H1-related SRTD exhibits significant phenotypic variability which cannot be reliably predicted by genotype but has some correlation with time of gestational presentation.

DYNC2H1 splicing variants causing severe prenatal short-rib polydactyly syndrome and postnatal orofaciodigital syndrome

The DYNC2H1 gene has been associated with short-rib polydactyly syndrome (SRPS), among other skeletal ciliopathies. Two cases are presented of distinctive phenotypes resulting from splicing variants in DYNC2H1. The first is a 14-week-old fetus with enlarged nuchal translucency, oral hamartoma, malformed uvula, bifid epiglottis, short ribs, micromelia, long bone agenesis, polysyndactyly, heart defect, pancreatic cysts, multicystic dysplastic kidney, megabladder and trident acetabulum. A ciliopathies NGS panel revealed two compound heterozygous variants in DYNC2H1: c.7840-18T>G r.7841_7964del p.Gly2614Aspfs*5 and c.11070G>A r.11044_11116del p.Ile3682Aspfs*2. Both variants were initially classified as variants of uncertain significance but were reclassified as likely pathogenic after PCR-based RNA testing. The second is an 11-year-old overweight male with multiple accessory oral frenula, median cleft lip and alveolar ridge, polysyndactyly, brachydactyly, normal rib length, and hypogonadism. Exome sequencing revealed two compound heterozygous variants in DYNC2H1: c.6315del p.(Thr2106Glnfs*7), classified as likely pathogenic, and c.3303-16A>G p.(?), classified as a variant of uncertain significance. PCR-based RNA testing suggested that c.3303-16A>G induces an in-frame deletion: r.3303_3458del p.Asp1102_Arg1153del, although the normal transcript is still produced. These results are consistent with both SRPS type I/III in the first case and orofaciodigital syndrome in the second, an unprecedented description. This work thus improves the clinical and molecular knowledge of the phenotypes associated with splicing variants in the DYNC2H1 gene.

Variant characterisation and clinical profile in a large cohort of patients with Ellis-van Creveld syndrome and a family with Weyers acrofacial dysostosis

BACKGROUND

Ellis-van Creveld syndrome (EvC) is a recessive disorder characterised by acromesomelic limb shortening, postaxial polydactyly, nail-teeth dysplasia and congenital cardiac defects, primarily caused by pathogenic variants in EVC or EVC2. Weyers acrofacial dysostosis (WAD) is an ultra-rare dominant condition allelic to EvC. The present work aimed to enhance current knowledge on the clinical manifestations of EvC and WAD and broaden their mutational spectrum.

METHODS

We conducted molecular studies in 46 individuals from 43 unrelated families with a preliminary clinical diagnosis of EvC and 3 affected individuals from a family with WAD and retrospectively analysed clinical data. The deleterious effect of selected variants of uncertain significance was evaluated by cellular assays.

MAIN RESULTS

We identified pathogenic variants in EVC/EVC2 in affected individuals from 41 of the 43 families with EvC. Patients from each of the two remaining families were found with a homozygous splicing variant in WDR35 and a de novo heterozygous frameshift variant in GLI3, respectively. The phenotype of these patients showed a remarkable overlap with EvC. A novel EVC2 C-terminal truncating variant was identified in the family with WAD. Deep phenotyping of the cohort recapitulated 'classical EvC findings' in the literature and highlighted findings previously undescribed or rarely described as part of EvC.

CONCLUSIONS

This study presents the largest cohort of living patients with EvC to date, contributing to better understanding of the full clinical spectrum of EvC. We also provide comprehensive information on the EVC/EVC2 mutational landscape and add GLI3 to the list of genes associated with EvC-like phenotypes.

Motor proteins, spermatogenesis and testis function

The role of motor proteins in supporting intracellular transports of vesicles and organelles in mammalian cells has been known for decades. On the other hand, the function of motor proteins that support spermatogenesis is also well established since the deletion of motor protein genes leads to subfertility and/or infertility. Furthermore, mutations and genetic variations of motor protein genes affect fertility in men, but also a wide range of developmental defects in humans including multiple organs besides the testis. In this review, we seek to provide a summary of microtubule and actin-dependent motor proteins based on earlier and recent findings in the field. Since these two cytoskeletons are polarized structures, different motor proteins are being used to transport cargoes to different ends of these cytoskeletons. However, their involvement in germ cell transport across the blood-testis barrier (BTB) and the epithelium of the seminiferous tubules remains relatively unknown. It is based on recent findings in the field, we have provided a hypothetical model by which motor proteins are being used to support germ cell transport across the BTB and the seminiferous epithelium during the epithelial cycle of spermatogenesis. In our discussion, we have highlighted the areas of research that deserve attention to bridge the gap of research in relating the function of motor proteins to spermatogenesis.