First familial cases of type 2 congenital erythrocytosis (ECYT2) with a Chuvash pathogenic variant in VHL gene in Poland: example of the clinical utility of next-generation sequencing in diagnostics of orphan diseases

In this article, we report familial cases of type 2 congenital erythrocytosis (ECYT2) in two siblings, a 2-year-old boy and his younger sister. Both patients were diagnosed based on laboratory findings including erythrocytosis, elevated hemoglobin levels, and hematocrit. Acquired erythrocytosis was excluded based on the clinical features and genetic analysis of JAK2/CALR/MPL genes. Next-generation sequencing was employed for older brother revealing NM_000551.4: c.598C>T, p.Arg200Trp homozygous variant in the VHL gene, the similar variant was detected in the younger sibling. Sequencing analysis confirmed the VHL c.598C>T heterozygous variant in both parents. To the best of our knowledge, these are the first confirmed cases of familial erythrocytosis type 2, also known as Chuvash type, in Poland.