HEXA and deafness: They also summarized the literature and found six reports in PWS patients with maternal disomy 15 with four other disorders with genes on chromosome 15 [Bloom syndrome (BLM gene at 15q26.1), Tay-Sachs disease (HEXA gene at 15q23), deafness-infertility (STRC gene at 15q15.3 and CATSPER2 gene at 15q15.3) and congenital ichthyosis (CERS3 gene at 15q26.3)].