CLN2 disease resulting from a novel homozygous deep intronic splice variant in TPP1 discovered using long-read sequencing

Neuronal ceroid lipofuscinosis type 2 (CLN2) is an autosomal recessive neurodegenerative disorder with enzyme replacement therapy available. We present two siblings with a clinical diagnosis of CLN2 disease, but no identifiable TPP1 variants after standard clinical testing. Long-read sequencing identified a homozygous deep intronic variant predicted to affect splicing, confirmed by clinical DNA and RNA sequencing. This case demonstrates how traditional laboratory assays can complement emerging molecular technologies to provide a precise molecular diagnosis.