2. The Disease
Condition involving the breakdown and use of fats and
cholesterol in the body
Harmful amounts of lipids accumulate in the spleen, liver,
lungs, bone marrow, and brain
Autosomal recessive pattern of inheritance (two copies of the
gene must be present)
Four variants: A, B, C1, and C2
Clinical feature include: severe liver disease, breathing
difficulties, developmental delay, seizures, increased muscle
tone, lack of coordination, problems feeding, and inability to
move eyes vertically.
No treatment
3. Variants
Types A and B: mutated SMPD1 gene
SMPD gene carries instructions for cells to produce,
sphingomyelinase, which processes lipids.
Mutations lead to deficiency of sphingomyelinase and
accumulations of cholesterol and lipids.
Types C1 and C2: mutated NCP1 or NCP2 gene
NCP1 gene produces a protein involved in the movement of
cholesterol and lipids within a cell.
May be a cholesterol pump, which is why its mutation leads
to the buildup of lipids and cholesterol in the cell membrane.
Plays a critical role in regulation of intracellular cholesterol
trafficking
NCP2 gene produces protein that binds and transports
cholesterol (not fully understood).
4. NCP1 v. NCP2 Gene
95% of patients have mutations in the NPC1 gene
Mapped at chromosome 18q11
NPC1 encodes a 1278 amino acid glycoprotein with 13
transmembrane domains.
Remainder of patients have mutations in the NPC2 gene (or
HE1 gene)
Mapped at chromosome 14q24.3
Encodes a small soluble lysosomal protein involved in
cholesterol binding.
Both genes have identical biochemical patterns suggesting that
the two proteins function together in cellular transport of
cholesterol, glycolipids, etc.
Work together to facilitate the intracellular transport of lipids
from the lysosome to other cellular sites.
Their precise functions and relationship remain unclear and are
currently the subject of intense investigation.
5. NCP1 Mutations
Over 130 mutations have been identified in NPC1
Results in Niemann-Pick Disease Type C1
Most found within a NPC1 specific cysteine-rich domain, suggesting that the
integrity of this region is crucial for normal functioning of the protein.
Mutations include: missense mutations, small deletions that generate
premature stop codons, intronic mutations predicted to alter splicing, and
point mutations.
Specific mutation examples:
exon 20 c.2932 C>T
c.882-28 A>G (note that patients with this mutation had fibroblasts
containing small amounts of mRNA without exon 7)
point mutation in exon 20 (causing frameshift and premature stop codon)
1553G-A transition (causing a splicing error of exon 9)
2783A-C transversion that results in a gln928-to-pro amino acid
substitution
3263A-G transition leading to a tyr1088-to-cys amino acid substitution
530G-A change in exon 5, resulting in a cys177-to-tyr substitution
4-bp deletion, TTAC
6. NCP2 Mutations
Results in Niemann-Pick Disease Type C2 and frontal lobe atrophy
Single amino acid changes prevents both cholesterol binding and the restoration of
normal cholesterol levels in mutant cells.
Specific mutation examples: 16 mutant alleles were identified representing only 5 different
mutations (all had a severe impact on the protein):
1. 2 nonsense mutations, glu20 to ter (E20X): associated with severe rapid disease course
• Results in a frameshift in exon 2, which generates a stop codon 4 codons downstream of
frameshift
• Lung involvement death from respiratory failure
1. Glu118 to ter substitution (E118X)
• Result of a G-to-T transversion at nucleotide 352 in exon 1 of HE1 gene
1. 1-bp deletion (27delG)
2. Splice mutation (IVS2+5G-A): very difference clinical presentation
• Milder phenotype
• Childhood onset of neurologic symptoms but prolonged survival
1. Missense mutation (S67P) resulting in reduced amts of abnormal HE1 protein.
*E20X was established as the most common mutant allele (56% frequency)
7. Lack of Knowledge
Unfortunately, the NCP1 and the NCP2
gene are not fully understood, which means
there is no proposed structure for either.
There is a structure for the NCP2 bovine
gene, but then again there is little
information about the actual mutations
involved.