Question

The human eye disease retinitis pigmentosa is caused by a loss of function mutation (rp) in the gene PRPF31. The disease is expressed when combined with wildtype allele 1 (rp+1) in a heterozygote, but not expressed when combined with wildtype allele 2 (rp+2) in a heterozygote. When comparing the number PRPF31 mRNA transcripts in the eyes of rp/rp+1 and rp/rp+2 individuals, researchers have found a higher number of functional PRPF31 mRNAs in the eyes of rp/rp+2 individuals. This is an example of ______ caused by haploinsufficiency or haplo-sufficiency________ when is rp occurs in the same genotype as rp+2.

Answer 1

Dominant mutations in the gene encoding the mRNA splicing factor PRPF31 cause retinitis pigmentosa, a hereditary form of retinal degeneration. The mechanism of incomplete penetrance in RP has been described as 'variant haploinsufficiency', in which the absence of a second wild-type PRPF31 allele is sometimes sufficient to produce disease, and sometimes is not, depending on the nature of the mutant allele. Haploinsufficiency may arise from a de novo or inherited loss-of-function mutation in the variant allele, such that it produces little or no gene product (often a protein). Although the other, standard allele still produces the standard amount of product, the total product is insufficient to produce the standard phenotype. This heterozygous genotype may result in a non-standard, deleterious or disease phenotype.

So RP is an example of loss of function mutation caused by haploinsufficiency when rp occurs in the same genotype as rp+2.

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