Novel molecular defects of the delta-aminolevulinate dehydratase gene in apatient with inherited acute hepatic porphyria

Cloning and expression of the defective gene for delta-aminolevulinate dehy dratase (ALAD) from the second of 2 German patients with ALAD deficiency po rphyria (ADP), who had been originally reported by Doss et al. in 1979, wer e performed. Cloning of cDNAs for the defective ALAD were performed using E pstein-Barr virus (EBV)-transformed lymphoblastoid cells of the proband, an d nucleotide sequences of cloned cDNA were determined. Two separate mutatio ns of ALAD cDNA were identified in each ALAD allele. One was G457A, termed "H1," resulting in V153M substitution, while the other was a deletion of 2 sequential bases at T-818 and C-819, termed "H2," resulting: in a frame shi ft with a premature stop codon at the amino acid position of 294. Using all ele-specific oligonucleotide hybridization, the mother of the proband was s hown to have an I-Il defect, while using genomic DNA analysis, the father w as shown to have an H2 defect. Expression of H1 cDNA in Chinese hamster ova ry cells produced an ALAD protein with only a partial activity (10.65% +/- 1.80% of the normal), while H2 cDNA encoded no significant protein. These d ata thus demonstrate that the proband was associated with 2 novel molecular defects of the ALAD gene, 1 in each allele, and account for the extremely low ALAD activity in his erythrocytes (similar to 1% of normal).