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A Chinese family was identified to have two patients with rickets, an adult female and a male child (proband), both exhibiting signs related to X-linked hypophosphatemic rickets (XLH). Gene sequencing analysis revealed a deletion of adenine at position 1985 (c.1985delA) in the PHEX-encoding gene. To investigate the relationship between this mutation and the pathogenicity of XLH, as well as analyze the effects of different dosages of PHEX gene mutations on clinical phenotypes, we developed a rat model carrying the PHEX deletion mutation. The CRISPR/Cas9 gene editing technology was employed to construct the rat model with the PHEX gene mutation (c.1985delA). Through reproductive procedures, five genotypes of rats were obtained: female wild type (X/X), female heterozygous (-/X), female homozygous wild type (-/-), male wild type (X/Y), and male hemizygous (-/Y). The rats with different genotypes underwent analysis of growth, serum biochemical parameters, and bone microstructure. The results demonstrated the successful generation of a stable rat model inheriting the PHEX gene mutation. Compared to the wild-type rats, the mutant rats displayed delayed growth, shorter femurs, and significantly reduced bone mass. Among the female rats, the homozygous individuals exhibited the smallest body size, decreased bone mass, shortest femur length, and severe deformities. Moreover, the mutant rats showed significantly lower blood phosphorus concentration, elevated levels of FGF23 and alkaline phosphatase, and increased expression of phosphorus regulators. In conclusion, the XLH rat model with the PHEX gene mutation dosage demonstrated its impact on growth and development, serum biochemical parameters, and femoral morphology.

Jessica María Forero-Delgadillo,1,2 Daniela Cleves,2,3 Vanessa Ochoa,1,2 Hernando Londoño-Correa,4 Jaime Manuel Restrepo,4 José Antonio Nastasi-Catanese,4,5 Harry Pachajoa2,5 1Pediatric Nephrology Fellow, Universidad Icesi-Fundación Valle de Lili, Cali, Colombia; 2Facultad de Ciencias de la Salud, Universidad Icesi, Cali, Colombia; 3Pediatrics Resident, Universidad Icesi-Fundación Valle de Lili, Cali, Colombia; 4Pediatric Nephrology Department, Fundación Valle del Lili, Cali, Colombia; 5Clinical Genetics Department, Fundación Valle del Lili, Cali, ColombiaCorrespondence: Harry PachajoaGenetics Division, Fundación Valle del Lili, Carrera 98 # 18-49, Cali, Valle del Cauca, ColombiaTel +57 2 3319090Email hmpachajoa@icesi.edu.coIntroduction: X-linked hypophosphatemic rickets is part of a larger group of hereditary diseases characterized by renal phosphate loss, which causes growth disorders, rickets, and osteomalacia. These conditions are characterized by disorders in phosphate equilibrium, which is essential for bone formation.Case Report: A female patient presented with bone deformities of the inferior extremities, prominent joints, and loss of teeth. She received initial management with oral calcium and orthotics in inferior extremities, with poor clinical outcome. PHEX gene sequencing revealed a pathogenic variant c.1601C>T (p.Pro534Leu).Discussion: XLHR is caused by mutations in the PHEX gene; to date, more than 460 mutations have been associated with the disease. Clinically, it is characterized by bowing of the lower extremities, decreased growth, musculoskeletal complaints, dental abscesses, and other clinical signs and symptoms of rickets.Keywords: XLHR, Phex gene, Colombia, pediatric, rickets