Study of FTMT and ABCA4 genes in a patient affected by age-related macular degeneration: identification and analysis of new mutations.
BACKGROUND
Age-related macular degeneration (AMD) is a multifactorial disease for which an involvement of alterations in the retinal ABC transporter gene (ABCA4) is still debated. Oxidative stress in retinal pigment epithelial cells has been postulated to contribute to the pathogenesis of the disease. Mitochondrial ferritin (FtMt), an iron-sequestering protein, is expressed in cell types characterized by high metabolic activity and oxygen consumption, including human retina, suggesting a role in protecting mitochondria from iron-dependent oxidative damage. Based on these findings we wanted to investigate whether mutations in this gene could be found in AMD patients.


METHODS
Mutational scanning of the FTMTgene was performed in a cohort of 50 patients affected by age-related macular degeneration. The ABCA4 gene was also scanned in one patient carrying an FtMt mutation. In silico analyses were carried out on the identified variants. The recombinant form of FtMt variant was expressed in Escherichia coli and biochemically characterized.


RESULTS
One patient was found to be heterozygous for two previously unreported genetic changes: a complex FtMt mutation (c.437_450delinsCT: delAGGACATCAAGAAGinsCT) and a missense p.Leu973Phe (c.2919G>T) mutation in exon 20 of ABCA4. Computational analyses predicted a severe structural impairment for FtMt variant and a mild destabilizing effect for ABCA4. E. coli expression of recombinant FtMt variant yielded a highly insoluble protein that could not be renatured under in vitro conditions suitable for wild-type ferritins.


CONCLUSIONS
Our findings suggest that the FtMt mutation may determine a condition similar to haploinsufficiency resulting in a reduced protection from iron-dependent oxidative stress in mitochondria.
Genomic Unit for the Diagnosis of Human Pathologies, Center for Translational Genomics and Bioinformatics, San Raffaele Scientific Institute, Milan, Italy. stenirri.stefania@hsr.it
Stefania
S
Stenirri
Paolo
P
Santambrogio
Marco
M
Setaccioli
Benedetta Gaia
BG
Erba
Maria
M
Pia Manitto
Ermanna
E
Rovida
Maurizio
M
Ferrari
Sonia
S
Levi
Laura
L
Cremonesi
D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000369:Aged, 80 and over; D001483:Base Sequence; D015331:Cohort Studies; D004252:DNA Mutational Analysis; D005260:Female; D005293:Ferritins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008268:Macular Degeneration / Q000235:genetics* / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
C056475:ABCA4 protein, human; D018528:ATP-Binding Cassette Transporters; D024101:Mitochondrial Proteins; C556634:mitochondrial ferritin, human; D005293:Ferritins