X-inactivation in Fabry disease.
BACKGROUND
Fabry disease is one of three X-linked lysosomal disorders. Because of X-chromosome inactivation (XCI), wherein there is (random) transcriptional silencing of one of the X-chromosomes in each female cell, females are mosaic for the expression of (some) X-linked genes. Thus, based on penetrance and expression, some females heterozygous for Fabry disease are symptomatic but not to the same degree as hemizygous males. The purpose of this study was to ascertain whether skewed X-inactivation favoring the mutant α-galactosidase A allele exists in our cohort of female heterozygotes of Fabry disease.


METHODS
All patients were evaluated by physical examination and ascribed disease-specific severity sub-scores for each of the four categories (cardiac, renal, neurological, general) and a total score using the Mainz Severity Score Index (MSSI). Blood samples were drawn for enzymatic activity of α-galactosidase A and for DNA extraction for analysis for α-galactosidase A mutations. XCI ratios were determined from peripheral blood leukocyte samples. The X-chromosome inactivation ratio was determined in each heterozygote.


RESULTS
Of 77 samples, only 18.2% were highly skewed (80/20). Only 14.3% of samples with nonsense mutations were highly skewed. There were no correlations between the XCI ratios and age, enzymatic activity of α-galactosidase A, MSSI sub-scores or total score, or with the clinical signs of cardiac involvement, neuropathic pain, or proteinuria.


CONCLUSIONS
These findings are comparable with others in Fabry disease, i.e., essentially the same as seen in normal non-elderly female population, raising the question of the mechanism underlying symptomatic phenotypic expression in heterozygous females with Fabry disease.
Gaucher Clinic, Shaare Zedek Medical Center, Hebrew University, Hadassah Medical School, Ein Karem, Jerusalem, Israel. elstein@szmc.org.il
Deborah
D
Elstein
Ella
E
Schachamorov
Rachel
R
Beeri
Gheona
G
Altarescu
D000328:Adult; D015331:Cohort Studies; D000795:Fabry Disease / Q000201:enzymology* / Q000235:genetics*; D005260:Female; D006801:Humans; D007668:Kidney / Q000201:enzymology; D008875:Middle Aged; D009154:Mutation; D009206:Myocardium / Q000201:enzymology; D009420:Nervous System / Q000201:enzymology; D010146:Pain / Q000201:enzymology / Q000235:genetics; D011507:Proteinuria / Q000201:enzymology / Q000235:genetics; D012720:Severity of Illness Index; D049951:X Chromosome Inactivation / Q000235:genetics*; D000519:alpha-Galactosidase / Q000097:blood / Q000235:genetics
D000519:alpha-Galactosidase