Oculocutaneous albinism type 3 (ORPHA:79433)
A form of oculocutaneous albinism (OCA) characterized by rufous or brown albinism and occurring mainly in the African population.
Epidemiology
Oculocutaneous albinism type 3 (OCA3) has an estimated prevalence of 1/8,500 individuals in Africa. It is rarely seen in other populations.
Clinical description
Visual anomalies, such as nystagmus, are frequently undetectable and patients usually present with one of two phenotypes: rufous OCA (ROCA), characterized by red-bronze skin color, blue or brown irises and ginger-red hair, or brown OCA (BOCA), characterized by light to brown hair and a light to brown or tan skin color. The clinical features of OCA3 have been considered as rather mild, and in the rare cases of non-African patients, reddish hair color has been reported. A Japanese girl was reported with having OCA3 who presented with blond hair and light skin (with a small Mongolian spot), was able to tan and was negative for nystagmus.
Etiology
OCA3 is caused by a mutation in the tyrosinase-related protein 1, TYRP1, gene located on chromosome 9p23. The majority of BOCA cases are seen in OCA2, but a few BOCA phenotypes have been reported with mutations in the TYRP1 gene, indicating OCA3.
Diagnostic methods
The clinical findings along with genetic testing are used to diagnose OCA3. Hypopigmentation of hair and skin are milder than other forms of OCA and some degree of tanning may be possible. Red reflex on transillumination of the iris and nystagmus are important clues to the diagnosis, however, some patients lack nystagmus or strabismus. Molecular genetic testing for a mutation in the TYRP1  gene can confirm diagnosis of OCA3 and distinguish it from other forms of OCA.
Differential diagnosis
Differential diagnoses include the milder forms of OCA (except for OCA1A), as well as syndromes with albinism as a feature such as Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, Griscelli syndrome, and Waardenburg syndrome type II.
Antenatal diagnosis
Prenatal testing is theoretically possible when the disease causing mutation in the parent is known, however, there are no reports of it having been performed.
Genetic counseling
OCA3 is inherited autosomal recessively and genetic counseling is recommended for at-risk couples (both individuals are carriers of a disease-causing mutation), informing them of the 25% risk of having an affected child at each pregnancy.
Management and treatment
Annual ophthalmologic examination is necessary and corrective lenses or glasses may be given when the patients have impaired visual acuity. Dark glasses may be needed to relieve photophobia. Strabismus surgery can be performed for functional or cosmetic reasons. Protection from sunlight is imperative and patients should wear clothing and sunscreen on exposed skin to prevent burning and reduce the risk of skin cancer. Annual skin examinations should also be performed to identify any pre-cancerous or cancerous lesions.
Prognosis
OCA3 is not life threatening and stabilizes after childhood. However, the medical and social consequences can have an impact on patient's daily life.

                            Last update: 
                            December 2020


                            - Expert reviewer(s): 
                            Dr Masahiro HAYASHI  - Dr Tamio SUZUKI