Loss-of-function OGFRL1 variants identified in autosomal recessive cherubism families.

Cherubism (OMIM 118400) is a rare craniofacial disorder in children characterized by destructive jawbone expansion due to the growth of inflammatory fibrous lesions. Our previous studies have shown that gain-of-function mutations in SH3 domain-binding protein 2 (SH3BP2) are responsible for cherubism and that a knock-in mouse model for cherubism recapitulates the features of cherubism, such as increased osteoclast formation and jawbone destruction. To date, SH3BP2 is the only gene identified to be responsible for cherubism. Since not all patients clinically diagnosed with cherubism had mutations in SH3BP2, we hypothesized that there may be novel cherubism genes and that these genes may play a role in jawbone homeostasis. Here, using whole exome sequencing, we identified homozygous loss-of-function variants in the opioid growth factor receptor like 1 (OGFRL1) gene in 2 independent autosomal recessive cherubism families from Syria and India. The newly identified pathogenic homozygous variants were not reported in any variant databases, suggesting that OGFRL1 is a novel gene responsible for cherubism. Single cell analysis of mouse jawbone tissue revealed that Ogfrl1 is highly expressed in myeloid lineage cells. We generated OGFRL1 knockout mice and mice carrying the Syrian frameshift mutation to understand the in vivo role of OGFRL1. However, neither mouse model recapitulated human cherubism or the phenotypes exhibited by SH3BP2 cherubism mice under physiological and periodontitis conditions. Unlike bone marrow-derived M-CSF-dependent macrophages (BMMs) carrying the SH3BP2 cherubism mutation, BMMs lacking OGFRL1 or carrying the Syrian mutation showed no difference in TNF-ɑ mRNA induction by LPS or TNF-ɑ compared to WT BMMs. Osteoclast formation induced by RANKL was also comparable. These results suggest that the loss-of-function effects of OGFRL1 in humans differ from those in mice and highlight the fact that mice are not always an ideal model for studying rare craniofacial bone disorders.

Preclinical Evaluation of a Modified Herpes Simplex Virus Type 1 Vector Encoding Human TGM1 for the Treatment of Autosomal Recessive Congenital Ichthyosis.

Autosomal recessive congenital ichthyosis (ARCI) is a diverse group of cornification diseases associated with severe clinical complications and decreased quality of life. Germline mutations in the TGM1 gene, which encodes the enzyme TGM1, are the predominant cause of ARCI. These TGM1 mutations trigger the abnormal epidermal differentiation and impaired cutaneous barrier function observed in patients with ARCI. Unfortunately, current ARCI therapies focus solely on symptomatic relief. Thus, there is a significant unmet need for therapeutic strategies aimed at correcting the TGM1 deficiency underlying ARCI. In this study, we investigated the ability of KB105, a gene therapy vector encoding full-length human TGM1, to deliver functional human TGM1 to keratinocytes. In vitro, KB105 efficiently infected TGM1-deficient human keratinocytes, produced TGM1 protein, and rescued transglutaminase enzyme function. In vivo studies demonstrated that both single and repeated topical KB105 administration induced TGM1 protein expression in the target epidermal layer without triggering fibrosis, necrosis, or acute inflammation. Toxicity and biodistribution assessments on repeat dosing indicated that KB105 was well-tolerated and restricted to the dose site. Overall, our results demonstrate that rescuing TGM1 deficiency in patients with ARCI through topical KB105 application represents a promising strategy for safely and noninvasively treating this debilitating disease.