TULP1 mutation in two extended Dominican kindreds with autosomal recessive retinitis pigmentosa.

The RP14 autosomal recessive Retinitis pigmentosa (arRP) locus has been mapped to a 2cM region of chromosome 6p21.3. TULP1 (the gene encoding tubby-like protein 1) is a candidate target for the disease mutation because it maps to the RP14 minimum genetic region and because a mutation in the highly homologous mouse tub gene leads to obesity, deafness and early progressive retinal degeneration. Here we report a splice-site mutation (IVS14+1, G-->A) that is homozygous in all affected individuals (N=33) and heterozygous in all obligate carriers (N=50) from two RP14-linked kindreds. The mutation was not observed in 210 unrelated controls. The data indicate that impairment of TULP1 protein function is a rare cause of arRP and that the normal protein plays an essential role in the physiology of the retina.

Identification and characterization of the mouse obesity gene tubby: a member of a novel gene family.

The mutated gene responsible for the tubby obesity phenotype has been identified by positional cloning. A single base change within a splice donor site results in the incorrect retention of a single intron in the mature tub mRNA transcript. The consequence of this mutation is the substitution of the carboxy-terminal 44 amino acids with 24 intron-encoded amino acids. The normal transcript appears to be abundantly expressed in the hypothalamus, a region of the brain involved in body weight regulation. Variation in the relative abundance of alternative splice products is observed between inbred mouse strains and appears to correlate with an intron length polymorphism. This allele of tub is a candidate for a previously reported diet-induced obesity quantitative trait locus on mouse chromosome 7.