Whole-Genome Sequencing of Retinoblastoma Reveals the Diversity of Rearrangements Disrupting RB1 and Uncovers a Treatment-Related Mutational Signature.

The development of retinoblastoma is thought to require pathological genetic changes in both alleles of the RB1 gene. However, cases exist where RB1 mutations are undetectable, suggesting alternative pathways to malignancy. We used whole-genome sequencing (WGS) and transcriptomics to investigate the landscape of sporadic retinoblastomas derived from twenty patients, sought RB1 and other driver mutations and investigated mutational signatures. At least one RB1 mutation was identified in all retinoblastomas, including new mutations in addition to those previously identified by clinical screening. Ten tumours carried structural rearrangements involving RB1 ranging from relatively simple to extremely complex rearrangement patterns, including a chromothripsis-like pattern in one tumour. Bilateral tumours obtained from one patient harboured conserved germline but divergent somatic RB1 mutations, indicating independent evolution. Mutational signature analysis showed predominance of signatures associated with cell division, an absence of ultraviolet-related DNA damage and a profound platinum-related mutational signature in a chemotherapy-exposed tumour. Most RB1 mutations are identifiable by clinical screening. However, the increased resolution and ability to detect otherwise elusive rearrangements by WGS have important repercussions on clinical management and advice on recurrence risks.

A rare and often unrecognized cause of hematochezia and tenesmus in childhood: solitary rectal ulcer syndrome.

Solitary rectal ulcer syndrome (SRUS) is an unusual disorder of childhood, which usually presents with rectal bleeding, mucous discharge, prolonged straining, tenesmus, and localized pain in the perineal area. After the first description by Cruveilhier, Madigan and Morson further detailed the clinical and pathologic features of SRUS in 1969. The pathogenesis of the syndrome is not well-understood. The postulated mechanism responsible for rectal prolapse in most cases seems to be excessive straining efforts during which high intra-abdominal pressure forces the anterior rectal mucosa firmly into the contracting puborectalis muscle. The anterior rectal mucosa is frequently forced into the anal canal and as a consequence becomes strangulated, causing congestion, edema, and ulceration. Histologically, the presence of fibromuscular obliteration of the lamina propria with disorientation of muscle fibers is characteristic, which could be secondary to chronic mechanical and ischemic trauma and inflammation by hard stools, and intussusception of the rectal mucosa. Although the syndrome is well-recognized in adults, the pediatric experience with this condition is limited and often remains unrecognized or misdiagnosed. A misdiagnosis has been reported in one fourth of adult cases, and the correct diagnosis usually delayed approximately 5 to 7 years. There are few pediatric case reports in English literature. Here, we describe 2 children with SRUS, aged 11 and 14 years, whose SRUS was diagnosed 2 and 6 years, respectively, after the onset of the first signs and symptoms.