Heterozygous loss of function

Ptacek It would also be interesting to look in the mice at seizure thresholds with proconvulsants. Again, you can imagine a heterozygous loss of function could give a predisposing factor in the human population that you would never see in homozygosity. 

Schaub et al. demonstrated that Mrp2/MRP2 is expressed in the proximal tubules in the kidney (241,242). In vivo study and clinical study supports that Mrp2/MRP2 is involved in the tubular secretion of organic anions. The urinary excretion rates of calcein and fluo-3 were three to four times lower in perfused kidneys from TR rats compared with normal rats, and the renal excretion of lucifer yellow was delayed in TR rats (243). Hulot et al. identified a heterozygous mutation, which results in a loss of function of MRP2, in the patient who showed delay of renal MTX elimination (244). 

The mutations causing the loss of the band s ability to form a puff represented a heterogeneous group. In regard to their functional character they could be joined into groups which differ in their expression in heterozygous combination with respective nonmutant strains. 

Loss or mutation that inactivates one copy of the gene can be tolerated because there is no functional deficit in the heterozygous condition. 

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