Expression and analysis of CLN2 variants in CHO cells: Q100R represents a polymorphism, and G389E and R447H represent loss-of-function mutations.

Late infantile neuronal ceroid lipofuscinosis (LINCL) is a fatal hereditary childhood disease. The gene underlying LINCL, CLN2, encodes a lysosomal enzyme, tripeptidyl peptidase I (TPP-I), deficiency in which leads to lysosomal accumulation of autofluorescent materials accompanied by severe neuronal atrophy. Mutational analysis was conducted to characterize different CLN2 alleles. Two probands of Romany origin were found to be homozygous for an allele that encoded a protein with two changes, designated Q100R+G389E CLN2. To distinguish potential polymorphisms from mutations, a recombinant expression system was used to investigate individual constructs. Elevated levels of TPP-I activity in CHO cells expressing Q100R CLN2 and background activity in CHO cells expressing G389E CLN2 clearly defines G389E as a pathogenic mutation and indicates that Q100R is a polymorphism. Association of the R447H mutation with a delayed onset form of LINCL in two separate families raised the question of whether R447H CLN2 retains residual activity. However, CHO cells expressing R447H CLN2 had TPP-I activity comparable to that of neo transfected cells, indicating that any residual activity was below the level of detection in this experimental system. Hum Mutat 18:165, 2001.