Novel TRPV4 variant causes a severe form of metatropic dysplasia.
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ABSTRACT:
SUBMITTER: Graversen L
PROVIDER: S-EPMC6132144 | biostudies-literature | 2018 Sep
REPOSITORIES: biostudies-literature
Publications
Novel <i>TRPV4</i> variant causes a severe form of metatropic dysplasia.
Graversen Lise L Haagerup Annette A Andersen Brian N BN Petersen Karin K KK Gjørup Vibike V Gudmundsdottir Gudrun G Vogel Ida I Gregersen Pernille A PA
Clinical case reports 20180720 9
We present a girl born with a frontal bossing, short neck, bell-shaped thorax, short limbs with prominent joints, and a tail-like coccygeal appendage. Genetic screening of <i>TRPV4</i> identified a novel de novo heterozygous missense variant. We believe the variant causes the severe form of metatropic dysplasia in this patient. ...[more]
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Project description:Metatropic dysplasia is a clinical heterogeneous skeletal dysplasia characterized by short extremities, a short trunk with progressive kyphoscoliosis, and craniofacial abnormalities that include a prominent forehead, midface hypoplasia, and a squared-off jaw. Dominant mutations in the gene encoding TRPV4, a calcium permeable ion channel, were identified all 10 of a series of metatropic dysplasia cases, ranging in severity from mild to perinatal lethal. These data demonstrate that the lethal form of the disorder is dominantly inherited and suggest locus homogeneity in the disease. Electrophysiological studies demonstrated that the mutations activate the channel, indicating that the mechanism of disease may result from increased calcium in chondrocytes. Histological studies in two cases of lethal metatropic dysplasia revealed markedly disrupted endochondral ossification, with reduced numbers of hypertrophic chondrocytes and presence of islands of cartilage within the zone of primary mineralization. These data suggest that altered chondrocyte differentiation in the growth plate leads to the clinical findings in metatropic dysplasia.
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Project description:Metatropic dysplasia is a congenital skeletal dysplasia characterized by severe platyspondyly, dumbbell-like deformity of long tubular bones, and progressive kyphoscoliosis with growth. It is caused by mutations in the gene TRPV4, encoding the transient receptor potential vanilloid 4, which acts as a calcium channel. Many heterozygous single base mutations of this gene have been associated with the disorder, showing autosomal dominant inheritance. Although abnormal endochondral ossification has been observed by histological examination of bone in a patient with lethal metatropic dysplasia, the etiology of the disorder remains largely unresolved. As dental pulp stem cells (DPSCs) are mesenchymal stem cells that differentiate into bone lineage cells, DPSCs derived from patients with congenital skeletal dysplasia might be useful as a disease-specific cellular model for etiological investigation. The purpose of this study was to clarify the pathological association between TRPV4 mutation and chondrocyte differentiation by analyzing DPSCs from a patient with non-lethal metatropic dysplasia. We identified a novel heterozygous single base mutation, c.1855C>T in TRPV4. This was predicted to be a missense mutation, p.L619F, in putative transmembrane segment 5. The mutation was repaired by CRISPR/Cas9 system to obtain isogenic control DPSCs for further analysis. The expression of stem cell markers and fibroblast-like morphology were comparable between patient-derived mutant and control DPSCs, although expression of TRPV4 was lower in mutant DPSCs than control DPSCs. Despite the lower TRPV4 expression in mutant DPSCs, the intracellular Ca2+ level was comparable at the basal level between mutant and control DPSCs, while its level was markedly higher following stimulation with 4α-phorbol 12,13-didecanoate (4αPDD), a specific agonist for TRPV4, in mutant DPSCs than in control DPSCs. In the presence of 4αPDD, we observed accelerated early chondrocyte differentiation and upregulated mRNA expression of SRY-box 9 (SOX9) in mutant DPSCs. Our findings suggested that the novel missense mutation c.1855C>T of TRPV4 was a gain-of-function mutation leading to enhanced intracellular Ca2+ level, which was associated with accelerated chondrocyte differentiation and SOX9 upregulation. Our results also suggest that patient-derived DPSCs can be a useful disease-specific cellular model for elucidating the pathological mechanism of metatropic dysplasia.
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