Five gene regions were found to have relatively low SNP coverage (less than 130 available SNPs): COL7A1 (72 SNPs, epidermolysis bullosa, OMIM:131750), POU3F4 (101 SNPs, hereditary deafness, OMIM:304400), AR (114 SNPs, Kennedy disease, OMIM: *313700), ATP7A (118 SNPs, Menkes syndrome, OMIM: 309400), and SMN1 (120 SNPs, spinal muscular atrophy, OMIM: 253300). The gene discussed is COL7A1; the disease is proximal spinal muscular atrophy.