Niemann-Pick disease (NP) is
an inherited
metabolic disorder in which
harmful quantities of a
fatty substance accumulate
in the spleen, liver,
lungs, bone marrow, and,
in some patients, the
brain. It is an autosomal
recessive
trait. The clinical
designations currently
subdivide patients into 4
categories.
In the first, called type
A, the children rarely
live beyond 18 months. The
second group, called type
B, is similar to type A,
however the brain is not
affected, and the patients
will therefore live longer.
The fatty material that
accumulates in types A and
B is called sphingomyelin.
This lipid is a major component of the
membrane of all cells in
the body. The metabolic
defect in types A and B is
insufficient activity of
an enzyme called sphingomyelinase
that catalyzes the decomposition of
sphingomyelin, which
arises from normal cell
turnover. These two types
are found mostly in the Ashkenazi Jewish population, and
within that population
there is a 1/90 carrier frequency.
The disease NP also
includes 2 other variant
forms called types C and
D. The disorder may appear
early in life or its onset
may be delayed into the
teen years. Both types are
characterized by an
inability to mobilize cholesterol in the nerve cells in the
brain where it accumulates
and causes malfunction of
these cells. The only
difference between these
two subtypes is that type
D arises in people with a
common ancestral
background in Nova Scotia. |