MOLECULAR ANALYSIS OF THE PPOX GENE IN ITALIAN PATIENTS WITH VARIEGATE PORPHYRIA (VP): IDENTIFICATION OF 3 NOVEL MUTATIONS

Patti E, Martinez di Montemuros F, Di Pierro E, Tavazzi D, Cappellini MD

 

Maggiore Policlinico Hospital, IRCCS, University of Milan, Italy

 

 

Variegate porphyria (VP; MIM 176200) is a low-penetrance, autosomal dominant disorder resulting from the partial deficiency of protoporphyrinogen oxidase (PPOX; EC 1.3.3.4), the 7th enzyme of the heme biosynthesis. VP is clinically characterized by photosensitivity and occasional acute neurovisceral attacks. Among the diagnostic criteria, the most powerful is the detection of a plasma fluorescent peak at 630 nm, present in roughly 70 % of the symptomatic VP patients. More than 100 molecular abnormalities have been so far identified in the PPOX gene as responsible for VP showing a high molecular heterogeneity. Few data are presently available on the Italian population. Aim of this study was to identify the molecular defect in the PPOX gene in 9 Italian unrelated subjects (1 male, 8 females) with suspected diagnosis of VP. The plasma peak is detected by fluorometric plasma scan from 580 to 650 nm. The coding region of PPOX gene was amplified by PCR in six fragments and directly sequenced. The plasma peak at 630 nm was markedly positive in 8 subjects and slightly positive in one. Eight different mutations have been identified among the 9 VP patients and summarized in the following Table.

 

Pt. Sex Mutation Exon Protein change Pl. peak (630 nm) Ref.
1
M
218 T>C
3
L73P
+
Whatley 1999
2
F
306 insC
4
FS>stop+41
++
This study
3
F
532 C>G
6
L178V
+
De Siervi 2000
4
F
694 G>C
7
G232R
+
Deybach 1996
5
F
745 insG
7
FS>stop+31
++
Deybach 1996
6
F
851 G>T
8
S248I
+/-
This study
7
F
1013 C>G
10
S338X
++
This study
8
F
1013 C>G
10
S338X
++
This study
9
F
1082 insC
10
FS>stop+19
++
Whatley 1999

 

The 1013 C>G mutations was identified in two unrelated subjects. The 306 insC, (FS>stop+41), 851 G>T (S284I) and 1013 C>G (S338X) mutations have been identified for the first time in this study and cause truncated or unstable proteins. 1082 insC seems to be quite common being found in 12% of VP patients in France and in another Italian study. The molecular analysis has been extended to 10 probands' family members with the finding of 7 mutation carriers. These results, suggest a high molecular heterogeneity for VP in Italy as described for other countries;