Molecular Mechanisms of Craniofacial and Dental Abnormalities in Osteopetrosis

A novel frameshift variant leads to familial osteopetrosis with variable phenotypes in a Chinese Han consanguineous family

Osteopetrosis, a group of highly heterogeneous genetic bone disorders, is characterized by deafness, increased bone density, hepatosplenomegaly, pancytopenia and intellectual disability. Osteopetrosis can be divided into three subtypes: autosomal recessive osteopetrosis (ARO), intermediate autosomal recessive osteopetrosis (IARO), and autosomal dominant osteopetrosis (ADO). CLCN7 has been reported to be the most common gene responsible for the ADO-II subtype. In this study, a novel variant, c.175dupA (p.Met59Asnfs*8), of CLCN7 was identified in a Chinese Han consanguineous family with suspected ADO-II. The proband was homozygous for the p.Met59Asnfs*8 variant and exhibited multiple severe phenotypes, including deafness, short stature, brittle bones, optic atrophy, hepatosplenomegaly, intellectual disability, cleft palate and recurrent infection. However, except for the mother of the proband, who presented a series of clinical phenotypes caused by bone marrow failure, all the other family members who were heterozygous had no obvious abnormal phenotypes. Our study suggested that the novel variant p.Met59Asnfs*8 in CLCN7 was very likely pathogenic factor in our suspected ADO-II family. The phenotypes of heterozygous carriers may be affected by incomplete penetrance. Loss of function of CLCN7 caused by nonsense-mediated mRNA decay (NMD) due to the frameshift variant was likely the underlying pathogenic mechanism. This study broadened the mutation spectrum of CLCN7, provided a foundation for timely and effective clinical intervention for related diseases, and demonstrates the importance of genetic counselling.

Association between serum homocysteine concentration level and tooth loss: a cross-sectional study from NHANES 2003-2006

INTRODUCTION

This cross-sectional study aimed to investigate the associations between serum homocysteine levels and missing teeth, as well as to explore the threshold effect of serum homocysteine levels on the number of missing teeth.

MATERIALS AND METHODS

This study involved 4746 participants (aged ≥ 40 years) from NHANES data 2003-2006. Negative binomial regression was used to assess the association between serum homocysteine levels and tooth loss. Non-linear and dose-response relationships were analyzed using smooth curve fitting and threshold effect analysis. In addition, we supplemented the relationship between serum homocysteine levels and tooth loss and conducted subgroup analysis to determine the impact of covariates on the relationship between serum homocysteine levels and tooth loss.

RESULTS

In a fully adjusted negative binomial regression model, higher levels of serum Hcy concentration in the Q2-Q4(Q2: IRR = 1.46, 95%CI (1.67,1.79)); Q3: IRR = 1.42, 95%CI (1.36,1.48); Q4: IRR = 1.47,95%CI (1.01,1.78)) groups increased the likelihood of tooth loss compared with quartile Q1 (low level of serum homocysteine). Threshold effect analysis revealed that the log2-transformed Hcy infection point was at 2.95 μmol/L.

CONCLUSION

The likelihood of tooth loss increased by 47% for each unit increase in serum homocysteine level. There was a non-linear positive correlation between serum homocysteine and tooth loss, with a threshold effect of approximately log2(Hcy) = 2.95 μmol/L. This link emphasizes the importance of maintaining appropriate homocysteine levels to prevent oral health problems.

FAM98 Family Proteins Play Distinct Roles in Osteoclastogenesis and Bone Resorption

There are three FAM98 family proteins (FAM98A/B/C) in humans and mice. Their physiological functions remain largely unknown. We have previously reported that Fam98a interacts with Plekhm1 in murine osteoclasts and functions in lysosome trafficking/secretion and bone resorption in osteoclasts in vitro. In this study, we found that all three Fam98 genes were expressed in precursor and mature osteoclasts. While the knockdown of Fam98c by a specific short-hairpin RNA (shRNA) in osteoclast precursors attenuated osteoclastogenesis, depletion of Fam98b by an shRNA specifically disrupted osteoclast lysosome trafficking and bone resorption with phenotypes similar to Fam98a shRNA-knockdown in our previous study. Loss of Fam98a in myeloid osteoclast precursors was dispensable for trabecular and cortical bone mass in mice, as well as osteoclastogenesis/bone resorption in vitro, possibly due to compensation by increased Fam98b expression in Fam98a-null osteoclasts. These findings indicate that the three Fam98 proteins play distinct roles in osteoclastogenesis and osteoclast function and need further investigation in future studies.

ADAM19 cleaves the PTH receptor and associates with brachydactyly type E

Brachydactyly type E (BDE), shortened metacarpals, metatarsals, cone-shaped epiphyses, and short stature commonly occurs as a sole phenotype. Parathyroid hormone-like protein (PTHrP) has been shown to be responsible in all forms to date, either directly or indirectly. We used linkage and then whole genome sequencing in a small pedigree, to elucidate BDE and identified a truncated disintegrin-and-metalloproteinase-19 (ADAM19) allele in all affected family members, but not in nonaffected persons. Since we had shown earlier that the extracellular domain of the parathyroid hormone receptor (PTHR1) is subject to an unidentified metalloproteinase cleavage, we tested the hypothesis that ADAM19 is a sheddase for PTHR1. WT ADAM19 cleaved PTHR1, while mutated ADAM-19 did not. We mapped the cleavage site that we verified with mass spectrometry between amino acids 64-65. ADAM-19 cleavage increased Gq and decreased Gs activation. Moreover, perturbed PTHR1 cleavage by ADAM19 increased ß-arrestin2 recruitment, while cAMP accumulation was not altered. We suggest that ADAM19 serves as a regulatory element for PTHR1 and could be responsible for BDE. This sheddase may affect other PTHrP or PTH-related functions.

Craniofacial disorders and dysplasias: Molecular, clinical, and management perspectives

There is a wide spectrum of craniofacial bone disorders and dysplasias because embryological development of the craniofacial region is complex. Classification of craniofacial bone disorders and dysplasias is also complex because they exhibit complex clinical, pathological, and molecular heterogeneity. Most craniofacial disorders and dysplasias are rare but they present an array of phenotypes that functionally impact the orofacial complex. Management of craniofacial disorders is a multidisciplinary approach that involves the collaborative efforts of multiple professionals. This review provides an overview of the complexity of craniofacial disorders and dysplasias from molecular, clinical, and management perspectives.

Maxillary osteomyelitis in a young female with osteopetrosis: unveiling an uncommon connection

Osteopetrosis encompasses a spectrum of conditions marked by heightened bone density due to faulty osteoclast-mediated bone resorption, leading to an accumulation of immature bone and thickened cortical structures. This condition gives rise to bone fragility, blood cell irregularities, nerve entrapment and growth challenges, all stemming from disrupted bone remodelling. Craniofacial distinctiveness, encompassing anomalies in the skull and jaw, is a frequent occurrence. Osteopetrosis presents a range of clinical signs, including facial and dental anomalies. The diagnostic process involves thorough clinical and radiological assessments, often obviating the need for genetic testing. Interestingly, few prior reports have delved into the specifics of craniofacial and dental issues in osteopetrosis. The presented case showcases rare occurrence of maxillary osteomyelitis. The diagnosis was established through a combination of history, clinical, radiographic and laboratory findings. The patient declined surgical intervention, leading to the implementation of conservative management involving regular irrigation alongside systemic antibiotic therapy.