Medulloblastoma in a child with osteoma cutis - a rare association due to loss of expression.

Objectives: Inactivating mutations result in varied phenotypes depending on parental origin. Maternally inherited mutations typically lead to hormone resistance and Albright's hereditary osteodystrophy (AHO), characterised by short stature, round facies, brachydactyly and subcutaneous ossifications. Paternal inheritance presents with features of AHO or ectopic ossification without hormone resistance. This report describes the case of a child with osteoma cutis and medulloblastoma. The objective of this report is to highlight the emerging association between inactivating germline mutations and medulloblastoma, aiming to shed light on its implications for tumor biology and promote future development of targeted surveillance strategies to improve outcomes in paediatric patients with these mutations.

Case Presentation: A 12-month-old boy presented with multiple plaque-like skin lesions. Biopsy confirmed osteoma cutis, prompting genetic testing which confirmed a heterozygous inactivating mutation. At 2.5 years of age, he developed neurological symptoms and was diagnosed with a desmoplastic nodular medulloblastoma, SHH molecular group, confirmed by MRI and histology. Further analysis indicated a biallelic loss of in the tumor.

Conclusions: This case provides important insights into the role of as a tumor suppressor and the emerging association between inactivating variants and the development of medulloblastoma. The case underscores the importance of careful neurological assessment and ongoing vigilance in children with known inactivating variants or associated phenotypes. Further work to establish genotype-phenotype correlations is needed to inform optimal management of these patients.