ABSTRACT
OCA1 type A) (Figures 19.1 and 19.2) to milder cases with hair pigmentation and changes after sun exposure with occurrence of nevi and freckles (Figure 19.3)
● Rarely, in milder cases there is the possibility of a heat-related pattern in the secretion of melanin, as occurs in Siamese cats
Extracutaneous symptoms
● Iris may be pink-red or blue-gray in milder cases and show transluscency on slit lamp examination (Figure 19.1)
● Strabismus (Figure 19.3), nystagmus, photophobia and poor vision
Figure 19.1 ● Foveal hypoplasia ● Even auditory evoked response may be abnormal, without hearing impairment
Complications ● Rare amelanotic melanomas
Figure 19.2 ● Sunburn, squamous and basal cell carcinomas (UV-induced)
Course
● In milder cases some degree of pigmentation of skin, hair and eye visible during childhood and adolescence
● In the same cases it is common to detect melanocytic nevi, ephelides and lentigines ● Nystagmus may ameliorate with age
Laboratory findings ● On histological examination, skin and hair-bulb structures are normal ● On ultrastructural examination, the first step of development of cytoplasmic organels with melaninrelated functions is normal
Genetics and pathogenesis
OCA1 is inherited in a recessive mode and is due to mutations of the tyrosinase gene. There is a wide variability in gene mutations, including stop-codon, missense, splicing, frameshift and deletions, responsible for the wide variation in phenotypes of these patients. A particular missense mutation renders the tyrosinase
gene temperature sensitive. Those patients with ‘temperature-sensitive cutaneous albinism’ develop, after puberty, some degree of pigmentation in the cooler areas of the body, producing the ‘Siamese cat’ pattern.
