Blood samples can be preserved by being placed on filter paper, dried, and frozen. Such samples, called dried blood spot (DBS) samples, can be transported from logistically challenging remote areas, and can be frozen for long-term storage. There are millions of such DBS samples stored in biobanks around the world, and they are often deeply phenotyped. This presents an opportunity for the study of genomic contributions to disease, often long before the disease's onset in the case of neonatal DBS samples. While genetic analysis in DBS samples is common and has yielded a large amount of high-quality research, no large-scale transcriptomic studies of DBS samples have been performed.  

 Here, we present evidence that RNA-sequencing can be successfully accomplished in neonatal DBS samples that have been stored at -20ºC for multiple decades. We find there is no loss of resolution in RNA-seq data obtained from such samples, and that we can successfully correct for bias due to non-random transcript degradation by using principal components. Upon performing differential expression analysis in individuals who go on to develop attention-deficit/hyperactivity disorder later on in life, we find evidence of differential expression of genes that are expressed in platelets and the cerebellum, and are involved in immune system response, cell-binding, and cell-signalling.