A genomic approach to mutation analysis of holocarboxylase synthetase gene in three Chinese patients with late-onset holocarboxylase synthetase deficiency.
OBJECTIVE
Multiple carboxylase deficiency (MCD, MIM:253270) is a common organic aciduria and caused by deficiency of either biotinidase or holocarboxylase synthetase (HLCS; EC 6.3.4.10). Patients commonly present during early infancy with acute metabolic derangements and severe metabolic acidosis. Recently, a late onset form of HLCS deficiency was also described. The different phenotypes (early and late presenting) may be related to a spectrum of mutations in HLCS gene. Applications of mutation analysis in HLCS had been limited previously by the requirement of cDNA from living tissue for study. We described here a genomic approach for molecular diagnosis of HLCS deficiency which we have used to detect mutations in Chinese patients who had the late-onset form of HLCS deficiency. In addition, a fibroblast cell line with MCD from Coriell Cell repositories was also studied.


METHODS
Three Chinese patients with late onset HLCS deficiency were studied. The genomic sequence of HLCS was retrieved and newly designed primers were used to cover all coding sequences of the gene. PCR products were analyzed by direct sequencing. Population allelic frequencies of mutations detected were determined by genotyping of control samples by restriction fragment length polymorphism.


RESULTS
We found a recurrent mutation, R508W, in the three unrelated Chinese patients. Two were homozygous for this mutation. The other patient was a compound heterozygote of R508W and a novel mutation, D634N. The results suggest that R508W may be an important and relatively prevalent disease-causing mutation in Chinese MCD patients. A fibroblast cell-line from an African patient revealed an additional novel mutation, R565X and a known mutation, V550M.


CONCLUSIONS
R508W is a recurrent mutation in Chinese MCD patients which is associated with the late onset phenotype. This new genomic approach for mutation analysis of HLCS gene provides new opportunities in studies of MCD.
Tang
Nelson L S
NL
Department of Chemical Pathology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, Hong Kong. nelsontang@cuhk.edu.hk
Hui
Joannie
J
Yong
Collin K K
CK
Wong
Lawrence T K
LT
Applegarth
Derek A
DA
Vallance
Hilary D
HD
Law
L K
LK
Fung
Simon L M
SL
Mak
Tony W L
TW
Sung
Y M
YM
Cheung
K L
KL
Fok
T F
TF
D044466:Asian People; D001483:Base Sequence; D019731:Carbon-Nitrogen Ligases / Q000235:genetics*; D002461:Cell Line, Transformed; D002675:Child, Preschool; D004252:DNA Mutational Analysis / Q000379:methods*; D017931:DNA Primers / Q000235:genetics; D005091:Exons; D005260:Female; D005347:Fibroblasts / Q000166:cytology; D006579:Heterozygote; D028922:Holocarboxylase Synthetase Deficiency / Q000235:genetics*; D006720:Homozygote; D006801:Humans; D007223:Infant; D008297:Male; D010641:Phenotype; D017354:Point Mutation; D012150:Polymorphism, Restriction Fragment Length
D017931:DNA Primers; D019731:Carbon-Nitrogen Ligases; C023312:holocarboxylase synthetases