Interestingly, in a most recent report, Baple et al. [50] identified a homozygous missense mutation in the PCNA gene in four individuals from an Amish pedigree with ataxia-telangiectasia-like disorder-2 (MIM #615919), presenting with a neurodegenerative phenotype characterized by DD, ataxia, and sensorineural hearing loss. The gene discussed is PCNA; the disease is dentin dysplasia.