Novel compound heterozygous STN1 variants are associated with Coats Plus syndrome

Aim: Coats plus syndrome (CP) is a rare autosomal recessive disorder, characterised by retinal telangiectasia exudates (Coats disease), leukodystrophy, distinctive intracranial calcification and cysts, as well as extra-neurological features including abnormal vasculature of the gastrointestinal tract, portal hypertension and osteopenia with a tendency to fractures. CP most frequently occurs due to loss-of-function mutations in CTC1. The encoded protein CTC1 constitutes part of the CST (CTC1-STN1-TEN1) complex, and three patients have been described with CP due to biallelic mutations in STN1. Together with the identification of homozygosity for a specific loss-of-function mutation in POT1 in a sibling pair, these observations highlight a defect in the maintenance of telomere integrity as the cause of CP, although the precise mechanism leading to the micro-vasculopathy seen at a pathological level remains unclear. Here, we present the investigation of a fourth child who presented to us with retinal exudates, intracranial calcifications and developmental delay, in keeping with a diagnosis of CP, and later went on to develop pancytopenia and gastrointestinal bleeding. Genome sequencing revealed compound heterozygous variants in STN1 as the likely genetic cause of CP in this present case. Methods: We assessed the phenotype to be CP and undertook targeted sequencing. Results: Whilst sequencing of CTC1 and POT1 was normal, we identified novel compound heterozygous variants in STN1 (previous gene symbol OBFC1): one loss-of-function-c.894dup (p.(Asp299Argfs*58)); and one missense-c.707T>C (p.(Leu236Pro)). Conclusion: Given the clinical phenotype and identified variants we suggest that this is only the fourth patient reported to date with CP due to mutations in STN1.