Expanding the clinical history associated with syndromic Klippel-Feil: A unique case of comorbidity with medulloblastoma.

Klippel-Feil syndrome (KFS) is an exceedingly rare constitutional disorder in which a paucity of knowledge exists about the disease and its associated morbidity and mortality. We present a 4-year-old male with KFS, who notably was also diagnosed with large-cell anaplastic medulloblastoma. We evaluated the genetic basis of co-occurring KFS and medulloblastoma and the role of MYO18B as related to medulloblastoma. Constitutional and somatic variant and copy number analyses were performed from DNA-based exome studies, along with RNA-sequencing of tumor tissue, to elucidate the genetic etiology of the co-existing disease states. We identified novel constitutional compound heterozygous frameshift variants (NM_032608.5: p.Leu2257SerfsTer16 and p.Arg2220SerfsTer74) each encoding a premature stop of translation in MYO18B, consistent with a diagnosis of KFS. We did not identify any somatic variants of known relevance or disease-relevant therapeutic targets in the tumor. The somatic copy number profile was suggestive of Group 3γ medulloblastoma. Relative to pediatric brain tumors, medulloblastoma, particularly, Group 3, had increased gene expression of MYO18B. In summary, coexisting constitutional and somatic diagnoses in this patient enabled the elucidation of the genetic etiology of KFS and provided support for the role of MYO18B in tumor suppression.