Case study of monozygotic triplets with identical pineal cysts. Is pineal cyst hereditary condition?

BACKGROUND: Pineal cysts are common incidental findings of uncertain etiology, and the potential contribution of genetic factors to their development remains poorly understood. This study aimed to investigate the possibility of a hereditary predisposition to pineal cysts by examining a unique case of identical pineal cysts in a set of monozygotic triplets and by surveying familial occurrence of pineal cysts within an institutional patient database. METHODS: A retrospective case study was conducted on 21-year-old monozygotic male triplets, each identified with a pineal gland cyst. All three underwent brain MRI with dedicated evaluation of the pineal region, independently reviewed by two board-certified neuroradiologists. One symptomatic triplet (T1) underwent surgical resection; peripheral blood and resected cyst tissue were subjected to whole-exome sequencing using an Agilent/Illumina NextSeq platform with variant analysis against the GRCh38 reference genome. Additionally, an institutional database of 243 patients with pineal cysts was reviewed for familial clustering. RESULTS: All three triplets presented with morphologically identical 14 mm pineal cysts, despite variable clinical presentations. WES identified a germline HERC2 nonsense variant (c.7114G > T, p.Glu2372Ter) in peripheral blood and a somatic INO80E frameshift mutation (c.42del) in cyst tissue, suggesting a possible two-hit model. Database review revealed eight additional individuals across four unrelated families with pineal cysts, all first-degree relatives, with identical cyst sizes noted in three of the four families. CONCLUSION: These findings provide novel evidence supporting a potential hereditary component in pineal cyst formation. While causality cannot be established from this case series alone, the observed familial clustering and identified genetic variants suggest that genetic factors may contribute to pineal cyst formation in selected cases and merit further investigation as additional familial or genetically characterized cases become available.