Identification of 58 novel mutations in Niemann-Pick disease type C: correlation with biochemical phenotype and importance of PTC1-like domains in NPC1.
The two known complementation groups of Niemann-Pick Type C disease, NPC1 and NPC2, result from non-allelic protein defects. Both the NPC1 and NPC2 (HE1) gene products are intimately involved in cholesterol and glycolipid trafficking and/or transport. We describe mutation analysis on samples from 143 unrelated affected NPC patients using conformation sensitive gel electrophoresis and DNA sequencing as the primary mutation screening methods for NPC1 and NPC2, respectively. These methods are robust, sensitive, and do not require any specialized laboratory equipment. Analyses identified two NPC1 mutations for 115 (80.4%) patients, one NPC1 mutation for 10 (7.0%) patients, two NPC2 mutations for five (3.5%) patients, one NPC2 mutation for one (0.7%) patient, and no mutations for 12 (8.4%) patients. Thus, mutations were identified on 251 of 286 (88%) disease alleles, including 121 different mutations (114 in NPC1 and seven in NPC2), 58 of which are previously unreported. The most common NPC1 mutation, I1061T, was detected on 18% of NPC alleles. Other NPC1 mutations were mostly private, missense mutations located throughout the gene with clustering in the cysteine-rich luminal domain. Correlation with biochemical data suggests classification of several mutations as severe and others as moderate or variable. The region between amino acids 1038 and 1253, which shares 35% identity with Patched 1, appears to be a hot spot for mutations. Additionally, a high percentage of mutations were located at amino acids identical to the NPC1 homolog, NPC1L1. Biochemical complementation analysis of cases negative for mutations revealed a high percentage of equivocal results where the complementation group appeared to be non-NPC1 and non-NPC2. This raises the possibilities of an additional NPC complementation group(s) or non-specificity of the biochemical testing for NPC. These caveats must be considered when offering mutation testing as a clinical service.
Park
Walter D
WD
Division of Laboratory Genetics, Department of Laboratory Medicine and Pathology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
O'Brien
John F
JF
Lundquist
Patrick A
PA
Kraft
Daniel L
DL
Vockley
Cate Walsh
CW
Karnes
Pamela S
PS
Patterson
Marc C
MC
Snow
Karen
K
D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics*; D002460:Cell Line; D002788:Cholesterol Esters / Q000032:analysis; D004252:DNA Mutational Analysis; D005787:Gene Frequency; D005816:Genetic Complementation Test; D005820:Genetic Testing / Q000379:methods; D005838:Genotype; D006023:Glycoproteins / Q000235:genetics*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D000077296:Niemann-Pick C1 Protein; D009542:Niemann-Pick Diseases / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism; D015513:Oncogene Proteins / Q000737:chemistry; D010641:Phenotype; D011110:Polymorphism, Genetic; D017434:Protein Structure, Tertiary; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D002788:Cholesterol Esters; D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; C106881:NPC1 protein, human; C104585:NPC2 protein, human; D000077296:Niemann-Pick C1 Protein; D015513:Oncogene Proteins; D033921:Vesicular Transport Proteins