Oculocutaneous Albinism, Ocular Albinism, Hermansky-Pudlak Syndrome, Chediak-Higashi Syndrome
Albinism is a group of congenital disorders of melanin production characterized by variable hypopigmentation and vision defects, including impaired visual acuity, nystagmus, strabismus, astigmatism, and photophobia. The complete or partial absence of pigment may affect the eyes, skin and hair (oculocutaneous albinism) or only the eyes (ocular albinism).
Additionally, there are also syndromic forms of albinism such as Hermansky-Pudlak syndrome and Chediak-Higashi syndrome.
The prevalence of all known forms of albinism is estimated to be 1:17 000 newborns.
Oculocutaneous albinism (OCA) is divided into seven types, which are caused by mutations in the respective genes: OCA1 (TYR), OCA2 (OCA2), OCA3 (TYRP1), OCA4 (SLC45A2), OCA5 (chromosome 4q24), OCA6 (SLC24A5), and OCA7 (C10orf11). All forms of OCA are inherited autosomal recessively.
Ocular albinism is caused by mutations in the GPR143 gene and is inherited in an X-linked manner.
Mutations in HPS1 (HPS1), AP3B1 (HPS2), HPS3 (HPS3), HPS4 (HPS4), HPS5 (HPS5), HPS6 (HPS6), DTNBP1 (HPS7), BLOC1S3 (HPS8), and BLOC1S6 (HPS9) genes are known to cause different types of Hermansky-Pudlak syndrome (HPS). HPS is inherited in an autosomal recessive manner and characterized by OCA, bleeding disorders, pulmonary fibrosis, and granulomatous colitis.
The LYST gene is know to be associated with Chediak-Higashi syndrome (CHS). CHS is inherited in an autosomal recessive manner and characterized by partial OCA, immunodeficiency, peripheral neuropathy, and bleeding tendency.
Indications for genetic testing:
- Confirmation of clinical diagnosis
- Carrier testing for at-risk family members
- Genetic counseling
- Prenatal diagnosis for known familial mutation