12466 Dual Bone Defect In Patients With Charge Syndrome

Abstract Disclosure: N. Reyes: None. R.J. Santen: None. S.M. Jan De Beur: None. R. Balasubramanian: None. Chromodomain Helicase DNA-binding protein 7 (Chd7) is an ATP-dependent chromatin modifier that mediates nucleosome remodeling. Chd7 mutations result in CHARGE syndrome characterized by coloboma, heart defects, choanal atresia, growth/developmental delay, ear abnormalities, and hypogonadotropic hypogonadism/Kallmann syndrome (IHH/KS). Testosterone has direct and indirect effects (through estrogen), to increase bone formation and decrease bone resorption. Untreated hypogonadism is associated with decreased bone density and fractures. Reports of fractures and low bone density in CHARGE syndrome patients have been attributed to sex hormone deficiency associated with hypogonadism. However, recent data from a Chd7 mouse knockout model suggests an intrinsic Chd7-related bone defect. In wild-type mice, Chd7 promotes osteogenic differentiation of mesenchymal stem cells. Chd7 deficient mice show markedly reduced osteoblasts. Thus, we propose, a dual bone defect in CHARGE syndrome resulting from impaired osteogenesis from CHD7 and sex steroid deficiency; and increased bone resorption due to lack of sex steroids. Here we present two individuals with CHARGE syndrome with markedly low bone density and literature review supporting the dual bone defect concept. Case 1 is a 30 yo male with a pathogenic CHD7 mutation, multiple congenital anomalies of CHARGE syndrome and hypogonadotropic hypogonadism. He had multiple fractures in his teen age years and a bone density Z score of -5.2 at the lumbar spine and -3.3 at the left femoral neck. Because he did not tolerate androgen therapy, a single infusion of zoledronic acid was administered with no further fractures for eight years following infusion. Case 2 is a male evaluated for IHH/KS and ultimately diagnosed with CHARGE Syndrome based on a pathogenic CHD7 mutation. Despite 7 years of testosterone therapy with full virilization, his bone density remained low at Z-score of -1.9 at the spine and -2.6 at the total hip. Results: Both patients had low bone density, one while untreated and the other after full virilization with exogenous androgens. This raises the question whether the bone defects were related to the CHD7 mutation, to androgen deficiency or both. To answer this question, a literature search examined bone density data in untreated patients with CHARGE syndrome versus IHH/KS. We found substantially lower bone density in untreated CHARGE patients Z score -3.46±0.36 (SEM) (n=13) versus IHH/KS -2.16 ±1.0 (n=4). Furthermore, the bone density was also lower in treated CHARGE patients -2.46±0.28 (n=6) versus IHH/KS -0.94±0.26 (n=140). Conclusion: These data, taken together, provide direct human evidence to support the concept that the CHD7-related CHARGE syndrome patients have a defect in both osteogenesis as well as an effect of sex steroid deficiency on bone. Presentation: 6/3/2024