To assess whether other known exon 11 missense mutations (identified as polymorphisms in the NHLBI Exome Sequencing Project [ESP] Exome Variant Server database of 13,006 chromosomes [release ESP6500]) (Exome Variant Server 2017) may cause XLSA or XLP, five novel missense mutations were identified as being the only significant enzyme variants in ALAS2 exon 11. This evidence concerns the gene ALAS2 and X-linked lymphoproliferative disease.