John M. Gardner

The mouse pink-eyed dilution gene: association with human Prader-Willi and Angelman syndromes.

Complementary DNA clones from the pink-eyed dilution (p) locus of mouse chromosome 7 were isolated from murine melanoma and melanocyte libraries. The transcript from this gene is missing or altered in six independent mutant alleles of the p locus, suggesting that disruption of this gene results in the hypopigmentation phenotype that defines mutant p alleles. Characterization of the human homolog revealed that it is localized to human chromosome 15 at q11.2-q12, a region associated with Prader-Willi and Angelman syndromes, suggesting that altered expression of this gene may be responsible for the hypopigmentation phenotype exhibited by certain individuals with these disorders.

Mutations of the human P gene associated with type II oculocutaneous albinism (OCA2)

Mutations in the human P gene lead to oculocutaneous albinism type 2 (OCA2, MIM #203200), the most common type of albinism in humans. The P gene encodes a 110 kDa protein that is associated with melanosomal membranes and contains 12 potential membrane spanning domains. The specific function of the P protein is currently unknown. We report 7 new mutations in the P gene associated with OCA2. This includes 6 missense mutations (S86R, C112F, A368V, T592I, A724P and A787V) and one frameshift mutation (1047del7). We also report 8 polymorphisms including one amino acid substitution, D/A257. We and others have found many polymorphisms of the P gene in the coding region, several of which result in amino acid substitutions, making molecular diagnosis problematic. In contrast to this is the tyrosinase gene associated with OCA1, with a limited number of polymorphic variations in the coding region. There is also no apparent clustering of P gene missense mutations in contrast to the clustering observed by the tyrosinase gene missense mutations that define functional domains of the protein. Further mutational analysis is needed to help define the critical functional domains of the P protein and to allow a definitive diagnosis of OCA2.

Mutations of the human P gene associated with Type II oculocutaneous albinism (OCA2). Mutations in brief no. 205. Online.

Hereditary predisposition to retinoblastoma is caused by germline mutations in the RB1 gene. Mutation analysis in this gene is important because knowledge of the causative mutation is often required for accurate risk prediction in relatives. We have performed RB1 gene mutation analysis in 45 patients with hereditary retinoblastoma. Screening by heteroduplex and SSCP analysis resulted in the identification of small mutations in 28 (62%) patients. Recurrent mutations, mostly CpG‐transitions, were found in 16 patients. Two patients with isolated bilateral retinoblastoma showed missense mutations, S567L and C712R, which have previously been reported in a patient with bilateral tumors and in a family with low penetrance, respectively. Twelve of the mutations identified here have not been reported to date. These include a novel missense mutation, L662P, which was identified in two bilaterally affected siblings and their mother with unilateral retinoma.