genetic test has the potential to lay out your future for you in the form of a
data sheet. Whether or not to take one to uncover a possible disease you may
have is a largely debated topic in society and the scientific world as such
tests have the power to change one’s outtake on life for the better or the
worse. In this opinionated piece, the topic of prospective parents taking a
genetic test for Niemann-Pick Disease will be discussed in greater detail.
valuable starting point would be finding out more about what Niemann-Pick
Disease (NPD) entails. It is an autosomal recessive genetic disorder, meaning only
homozygous-recessive individuals have the disease, where lipids accumulate in cells
as a result of improper metabolism. The disorder has three main types; NPD Types
A and B are characterized by hepatosplenomegaly, failure to thrive, neurodegeneration, and in severe Type
B cases, lung infections. Type C (NPC) is much rarer and is characterized
by an inability to transport cholesterol. Death is common at around 2-4 years old, but some may survive until
adulthood. Symptoms of Niemann-Pick Disease include jaundice, motor
skill difficulties, seizures, decreased appetite, swelling of the abdomen, and
ataxia to name a few. The biochemistry involved with NPD connects to genetic mechanisms.
NPD Types A and B are caused by mutations in the SMPD1 gene, which codes for acid
sphingomyelinase (ASM) that cleaves sphingomyelin in lysosomes. Mutations cause
a lack of ASM and thus copious sphingomyelin in areas such as the spleen and
liver. In NPC, mutations in the NPC1 and NPC2 genes that code for proteins
results in the inability to process cholesterol in lysosomes and endosomes. Currently
there is no treatment for NPD, but actions can be taken to decrease symptoms,
such as enzyme replacements and gene therapies. Bone marrow and liver
transplantation have seen promising results in Type B individuals. For NPC,
low-cholesterol diets can decrease liver cholesterol, and Miglustat has been
approved by Canada as a drug to treat NPC neurological complications. In terms
of NPD prevalence, Ashkenazi Jews been genetically screened for NPA mutations,
showing a frequency of the disease of about 2-3 individuals per 100,000. The
commonness for Type A and B is about 1 in 250,000, and NPC data suggests a 1 in
150,000 chance. Furthermore, Nova Scotian French Acadians and New Mexico Hispanic
populations have shown NPC1 gene mutations.
there are unaffected prospective parents with family histories of NPD, they
might be interested in finding out if they are carriers for disease alleles and
the chances of their children being affected. One way to evaluate one’s disease
likelihood is through skin assays such as biopsies. Biopsies are procedures where a sample of skin is taken
and examined under a microscope. A diagnosis of Niemann-Pick Disease Type A or
B can be made if cells are reporting lower than average sphingomyelinase
activity. For NPC, cholesterol storage and transport mechanisms are examined in
cells and a diagnosis is made if molecular machinery is not fully functioning.
This method is more biochemically-driven while a genetic test can provide
DNA-sequencing information. A genetic test can be performed on a blood
sample to determine any alterations in proteins, genes, or chromosomes and help
conclude if an individual is prone to a genetically-heritable condition.
Identification of alleles can also provide information about past generations
and future children. Since
Niemann-Pick Disease is recessive, if both parents are carriers, there is a 25%
chance that their child will have NPD, 50% chance they will be a carrier and
not show symptoms, and 25% chance that they do not have any disease alleles.
a genetic test has its advantages. It can allow one to become aware of a
genetic disease and provide the time to take action earlier. Genetics
professionals are there for support and all the information one needs to know
before and after taking a test to assist in making the best decisions possible.
Also, physical risks from blood sampling are low, but prenatal testing is slightly
riskier. Sampling of chorionic villi cells (CVS) from the placenta can lead to
infections and has a 0.7% chance for miscarriage. Other disadvantages include
cost, as a test can range from $15-60 for an infant to ~$100-$2000 for an
adult, depending on the intricacy of the test. The results could have a large
emotional impact on the individual and the extended family. Additionally, symptoms,
severity, and prognosis cannot be uncovered, only if the individual has a gene
variant associated with the disorder. Many genetic tests cannot screen for all
alleles of a mutation, or can show false positive or false negative results,
leading to further accuracy concerns.
my opinion, based on the plethora of scientific research on this topic, I would
recommend a genetic test to prospective parents who have family histories of
Niemann-Pick Disease. A genetic test can be taken by these couples to identify
if they are carriers for any NPD alleles and how their future children could be
affected. The child will only be affected, at a 25% chance, if both individuals
receive results stating they are carriers. If this is the situation and the
parents decide to conceive, prenatal testing is recommended. The risk for
miscarriage during CVS is 0.7% and provides fast and accurate to 98-99% results.
If NPD results for the child come back as positive, the parents can decide whether
or not they would like to proceed with the pregnancy knowing the severity of
the disease, early death, and the lack of definitive treatments available. If a
test is going to be taken, the individuals should always go through genetic
counselling with a trusted professional to be well-versed on information such
as the chances of receiving false negative or false positive data. Implementing
a strong confidentiality agreement of the results is also recommended. As a
conclusive note, a genetic test only advises one of their genetic information
and should not be making decisions for the individual. A test brings light to a
situation and provides more knowledge one may not have already known, but what
one does with that information is their choice, whether or not they want to be
influenced by the test results.