Do pigmented naevi in albinism provide evidence of tyrosinase positivity?

Oculocutaneous albinism

Oculocutaneous albinism represents a group of inherited skin disorders characterized by a generalized reduction of cutaneous, ocular and pilar pigmentation from the time of birth. Oculocutaneous albinism types 1 and 2 are the most common, but several other types have been described. A defect in the melanin synthesis pathway, resulting in reduced formation of melanin, is responsible for oculocutaneous albinism. Aetiology, clinical manifestations, diagnosis and management are discussed.

Prenatal diagnosis of oculocutaneous albinism by analysis of the fetal tyrosinase gene

Tyrosinase-negative oculocutaneous albinism, the most severe subtype of a heterogeneous group of albinism, is an autosomal recessive trait caused by mutations in the tyrosinase gene. Prenatal diagnosis had been made previously only by evaluating fetal skin obtained by biopsy, an invasive procedure that cannot be performed earlier than 19 weeks of gestation. A pregnant mother of a 9-year-old Japanese boy with tyrosinase-negative oculocutaneous albinism wanted a prenatal diagnosis. Polymerase chain reaction amplification and allele-specific oligonucleotide hybridization revealed that the child is homozygous and the parents heterozygous for the pathologic mutation of the tyrosinase gene in exon 2 (single base insertion) but not for the one in exon 1. Prenatal diagnosis was made by analyzing the tyrosinase gene in fetal cells obtained by amniocentesis at 14 weeks of gestation, which demonstrated that the fetus was heterozygous for mutant tyrosinase gene. Pregnancy was therefore continued and a normal male infant was born. This procedure, the analysis of the fetal genomic tyrosinase DNA, is a rapid and reliable approach to the prenatal diagnosis of oculocutaneous albinism at a relatively early stage of pregnancy and is safer and less invasive than previous methods using fetal skin biopsy.