Abstract: This disclosure relates to computationally efficient processing of sequencing data relating to amyotrophic lateral sclerosis (ALS). A processor receives unaligned training reads and determines training sub-sequences from them. The processor then counts the training sub-sequences in a control group and in a group diagnosed with ALS and determines a measure of change, for each of the training sub-sequences, in the counting between the control group and the group with ALS. The processor further selects a subset of training sub-sequences that are distal from a mean value of the measure of change and then receives testing sequencing data comprising multiple unaligned testing reads. The processor determines sub-sequences from the testing reads, counts the sub-sequences that are in the subset, and determines a diagnostic output value related to ALS for the sample based on the counting of the testing sub-sequences that are in the subset.