Combined de-novo mutation and non-random X-chromosome inactivation causing Wiskott-Aldrich syndrome in a female with thrombocytopenia.
OBJECTIVE
Disorders linked to mutations in the X chromosomes typically affect males. The aim of the study is to decipher the mechanism of disease expression in a female patient with a heterozygous mutation on the X-chromosome.


METHODS
Clinical data was extracted from the Canadian Inherited Marrow Failure Registry. Genomic ribonucleic acid (DNA) and complementary DNA (cDNA) underwent Sanger sequencing. Protein analysis was performed by flow cytometry. X-inactivation patterns were analyzed by evaluating the DNA methylation status and cDNA clonal expression of several genes on the X-chromosome. SNP array was used for molecular karyotyping of the X-chromosome.


RESULTS
A female with thrombocytopenia, eczema and mild T-lymphocyte abnormalities with extensive negative diagnostic testing, was suspected to have Wiskott-Aldrich syndrome (WAS)/X-linked thrombocytopenia. Although the girl had a mutation (c.397G > A, p.E133K) in only one allele, she was found to have an extremely skewed X-inactivation pattern and no expression of the WAS protein. Family studies using DNA methylation analysis and cDNA clonal expression of several genes on the X-chromosome demonstrated that the patient developed de-novo non-random inactivation of the X-chromosome that does not carry the mutation. Genome-wide high-density molecular karyotyping excluded deletions and amplifications as a cause for the non-random inactivation of one X-chromosome.


CONCLUSIONS
Our study emphasizes the need to test selected female patients with complete or incomplete disease expression for X-linked disorders even in the absence of a family history.
Genetics and Genome Biology Program, Research Institute, University of Toronto, Toronto, Ontario, Canada.
Boonchai
B
Boonyawat
Santhosh
S
Dhanraj
Fahad
F
Al Abbas
Bozana
B
Zlateska
Eyal
E
Grunenbaum
Chaim M
CM
Roifman
Leslie
L
Steele
Stephen
S
Meyn
Victor
V
Blanchette
Stephen W
SW
Scherer
Sabina
S
Swierczek
Josef
J
Prchal
Qili
Q
Zhu
Troy R
TR
Torgerson
Hans D
HD
Ochs
Yigal
Y
Dror
D000917:Antibody Formation / Q000235:genetics; D019175:DNA Methylation / Q000235:genetics; D005260:Female; D050172:Genes, X-Linked / Q000235:genetics; D005838:Genotype; D006801:Humans; D007109:Immunity / Q000235:genetics; D007223:Infant; D007231:Infant, Newborn; D046228:Microarray Analysis; D009154:Mutation / Q000235:genetics; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide; D013601:T-Lymphocytes / Q000276:immunology*; D013921:Thrombocytopenia / Q000175:diagnosis* / Q000235:genetics; D014923:Wiskott-Aldrich Syndrome / Q000175:diagnosis* / Q000235:genetics; D051300:Wiskott-Aldrich Syndrome Protein Family / Q000235:genetics / Q000378:metabolism*
D051300:Wiskott-Aldrich Syndrome Protein Family