Cowden syndrome: new clinical features in a large family; joint hyperextensibility, dental abnormalities and gingival enlargement.

A 4-year-old boy presented with his mother to genetics in the 1980s, with a family history (FH) of macrocephaly and intellectual disability (ID). He remained undiagnosed until his mother developed multiple cancers and was diagnosed with Cowden syndrome (CS) in 2017, a rare, multisystem cancer predisposition syndrome. CS was then confirmed in multiple family members. Clinical examination revealed potentially novel features; gingival enlargement, dental abnormalities and joint hyperextensibility. These features could contribute to revised hamartoma tumour syndrome, National Comprehensive Cancer Network, minor diagnostic criteria. The paediatric CS phenotype is still emerging and features expressed in this family during childhood could potentially aid paediatric diagnosis. This case reminds clinicians to seek genetic input for testing when macrocephaly is identified alongside, a personal or FH of ID, early-onset tumours (especially breast, bowel or thyroid) or multiple tumours. Thus detailed FH is pivotal to earlier CS diagnosis and improved patient outcomes.