Niemann-Pick+Disease

Niemann-Pick Disease is rare autosomal recessive gene mutation that is recognized by the accumulation of lipids in various cells throughout the body and is classified as a lysosomal storage disease. There are four major types of the disease, each with their own unique set of deficiencies and symptoms. Types A and B are characterized the absence of sphingomyelin metabolizing enzyme and accumulation of this lipid in visceral cells; Types C and D are involve the body losing the ability to properly breakdown lipids due to a lysosomal storage problem. Studies on Niemann Pick Disease Type C patients show they have a substantial reduction in their thalamus, superior cerebellum and insular cortex; therefore, Niemann-Pick Disease in general is a neurogenetic disease. Research and understanding of this disease is important, because there is still no overall cure; however, there are various therapies being studied that may eventually develop into an umbrella therapy.

toc =1. Classifications, Symptoms & Demographic=

The different types of Niemann-Pick Disease are classified by the deficiency that causes the disease in the first place. Even though Niemann-Pick Disease is a neurogenetic disease, not all types affect the central nervous system (CNS).

1.1 Type I (A & B)
Types A and B (NPA and NPB, respectively) are the result of a gene mutation that knocks out the production of the enzyme acidic sphingomyelinase (ASM). ASM is responsible for metabolizing the fat molecules sphingomyelin; because these fat cells are found in every cell in the body, a deficiency in ASM leads to sphingomyelin build up in all cells. Eventually, the cell will die and this leads to organ malfunction. Type I Niemann-Pick Diseases can be found in any race/ethnicity, but NPA is more prominent in Eastern European Jewish populations. Symptoms for NPA include jaundice, enlarged liver, brain damage, and loss of early motor skills that worsen over time. It has been well documented that Type A Niemann-Pick Disease occurs in newborns within the first six months of life and is fatality is guaranteed. Type B Niemann-Pick Disease affects humans in late childhood to adolescence; many of NPB’s symptoms overlap NPA symptoms. However, there is minimal CNS/PNS involvement, such as poor motor skill development in newborns. [4] [5]

1.2 Type II (C & D)
In contrast to Type I Niemann-Pick Diseases, the body’s inability to breakdown and transport cholesterols and other lipids in vital organs cause the Type II diseases. Type C Niemann-Pick (NPC) is characterized by the buildup of cholesterol in the liver and spleen, and lipids in the brain; also causes gangliosides (e.g. GM2 and GM3) to accumulate in white and gray matter. NPC is the result of an autosomal recessive mutation in either gene NPC1 or NPC2; however, most (95%) humans, mice and feline patients with Niemann-Pick Disease Type 2 have a mutation in NPC1. [5] Another complication arises from NPC is the neurological damages that affect axonal and dendritic morphology, affect neuronal-glial interactions, and disrupt axonal transport and intracellular lysosomal transport. Niemann-Pick Disease Type C can occur to a larger age group from infants to adults, and has many more symptoms. Some symptoms include enlarged spleen/liver, seizures, dystonia, dementia, irregular speech and sudden loss of muscle tone leading to falls. [4] In patients with adult-onset of NPC it is common to see significant neuropsychiatric disturbances, such as schizophrenia-like psychosis. [7] The following link shows the progression of two children as they age with NPC: Progression of NPC.

Type D Niemann-Pick (NPD) specifically involves problems with cholesterol transportation between brain cells, and causes symptoms like Type C. All documented cases of NPD can only be found in Yarmouth County, Nova Scotia, in humans of French descent. [4]

=2. Methods of Diagnosis=

There are many methods to diagnose a disease, but not all techniques will lead to the same or correct diagnosis. There are three well used practices of diagnosing Niemann-Pick Disease: genetic testing, laboratory (physiological) testing, and neuroimaging techniques.

2.1 Laboratory (Physiological) Testing
The most common way to diagnose Niemann-Pick Diseases of all types is to run a series of tests on the concentrations and compositions of various proteins, lipids and other molecules that are found within the body. One of the tests analyze tissue samples (e.g. bone marrow, spleen, liver, and lymph nodes) under a light microscope for signs of foaming cells, and examining skin biopsies under an electron microscope to observe the vitality of fibroblasts. Skin fibroblasts are also taken to use in the filipin test, where fibroblasts are cultures in an LDL-enriched medium and then stained with filipin. Niemann-Pick Disease Type C positive cells will typically be strongly fluorescent (cholesterol filled) perinuclear vesicles. The filipin test is the best method of diagnosing NPC except in infant diagnoses, where genetic testing is the most recommended and successful method. When diagnosing Niemann-Pick Type I Diseases (Figure 2), it is ideal to obtain the ASM enzymatic activity levels in blood lymphocytes and skin fibroblasts. [8]

2.2 Genetic Testing
Although the methods of genetic testing are well understood and performed on a daily basis, there are variations of the mutations in //NPC1// and //NPC2// that complicate the process. For example, sequencing the two genes can show in detail any abnormalities that can lead to NPC; //NPC1// is located on chromosome 18, q11-q12, and //NPC2// is located on chromosome 14, q24.3. This method is preferred for prenatal testing, because the biochemical tests require comparisons with affected family members who have to have a classic biochemical phenotype (Figure 2). [8]



2.3 Neuroimaging Techniques
Neuroimaging techniques used on Niemann-Pick Disease patients are used for the purpose of tracking changes in brain physiology and activity as the disease progresses. Magnetic resonance imaging is used to view the three-dimensional changes in the overall brain volume. To identify any disruptions in brain functioning, researchers and physicians can use a variety of function detection and imaging techniques such as [|functional MRIs], and [|magneto-encephalography] (MEG).

=3. Nervous System Degeneration=

As mentioned in the earlier section, both Type A and C of Niemann-Pick Disease can lead to extensive brain damage. Many studies have been done to locate the areas of damaged/lost brain tissue in NPA and NPC patients. This research alongside the well-established understanding of what those brain areas control in the body, researchers are able to list the changes in the patients’ behaviour, motor skills and memory.

3.1 Loss of Brain Tissue
Walterfang M, //et al//. conducted a study on white and gray matter alterations in the brains of NPC patients, focusing on adults. When comparing the MRIs of the controls against those of the NPC patients, the researchers were able to map out the most common areas of brain tissue loss. They determined that with Niemann-Pick Disease Type C, patients’ brains suffer loss of white matter is all areas of the brain, but localized loss of gray matter (the cell bodies). [7]

The changes to gray matter appear is the later stages of the disease; there is also a highly significant decrease is gray matter volume in areas such as the left and right hippocampus, parahippocampal gyrus, thalamus and the right putamen (figure to the right). These findings were interpreted to be evidence for a pattern of gray matter volumetric change, which is more visible in the adult patients with later stages of NPC (Figure 3). The researchers confirmed they didn’t know why these specific areas were affected, but referenced the known data on cats with NPC. These cats suffered the same effects of decreased lysosomal activity in the CNS, but only their cerebellar Purkinje neurons were lost. The NPC cats also had excessive ectopic dendritic sprouting in areas of GM2 ganglioside accumulation. Researchers also observed axonal spheroid in GABAergic neuronal brain tissue (e.g. cerebellum, hippocampus and basal ganglia), which is well known to be a phenotype of storage disorders that lead to neurological diseases. There is also the formation of neurofibrillary tangles (NFTs) in basal ganglia, cerebral cortex, and the hippocampus (specifically CA1 and CA2). [7]

The white matter damage of NPC is more widespread rather than the gray matter damage; it should be noted that cholesterols are lipids and so are the myelin sheaths that give white matter their white appearance. The limited transport of cholesterol to distal axons in the brain tissue can lead to abnormal axonal branching and reduced axonal number in long association & commissural tracts (e.g. corpus callosum) (refer to Figure 4). Another complication of Niemann-Pick Disease Type C is the disruption of myelination as a result of proteins’ abnormal interaction with reduced myelination. [7]



3.2a Behavioural
For the reason that Niemann-Pick Disease is such a rare disease, it is not always the first diagnosis that physician thinks of; therefore, there may be patients who exhibit symptoms of schizophrenia and/or psychosis and are not considered Niemann-Pick Disease patients. In one case that was handled by the Mayo Clinic Rochester, a woman was misdiagnosed because her initial symptoms resembled a schizophrenia-like psychosis; however, 15 years after she was diagnosed with NPC. This patient’s symptoms progressed in the following order: depression (46 years old), delusions, mood lability, hypervigilance, auditory hallucinations, paranoia, seizures, and virtually mute (61 years old).

3.2b Motor
As mentioned in an earlier, NPC patients suffer cerebellar degeneration that leads to cerebellar ataxia (a loss of control over voluntary coordinated muscle movement caused by cerebellar damage). Intention tremors, dystonia and dysmetria are other problems affect the motor function of the NPC patients. The most common motor dysfunction are low frequency, variable, irregular movements that occur most when the patient is moving; these movements are nonexistent when the patient is inactive (not moving).

3.2c Memory
There are many areas in the brain that are known to be involved in forming, storing and retrieving memories, and one of the most important areas is the hippocampus. InNPC patients, it is well typical to see problems with amyloid precursor protein processing; NPC patients have similar symptoms similar to Alzheimer Disease patients. One of the most common Alzheimer Disease symptoms is memory loss, which is seen in NPC patients on a smaller scale. In Niemann-Pick Disease Type A patients, the deficiency in ASM causes changes to short-term synaptic plasticity. From studying the chemical interactions across the synapses of CA1 (in hippocampus slices), Camoletto P.G. //et al//. show the accumulation of sphingomyelin causes smaller synapses, but both had a similar amount of neurotransmitters receptors (Figure 5). They suggest there is a compensation of the number of neurotransmitter receptors in that synapse and this prevents degeneration of the hippocampus’s function, while the size itself will continue to decrease (Figure 6). [3]

=4. Treatment Options=

4.1 Known Therapies
At the moment there are no cures/treatments for any form of Niemann-Pick Disease. The only thing physicians can do for Niemann-Pick Disease patients is to treat a specific symptom of the disease, such as bone marrow transplantation in NPA patients. [2]

4.2a Replacement of Deficient Enzymes
Nielsen, G.K. //et al//. use enzyme replacement therapies (ERT) to fix the negative effects of mice with Niemann-Pick Disease Type C, which lack the //NPC2// gene. ERT’s purpose is for endogenous lysosomes to accept exogenously supplied lysosomal enzymes, using mannose-6-phosphate receptors and mannose receptors. The first step was to isolate the NPC2 enzymes, which cannot be directly attained from tissues; so they got the enzyme from bovine milk (can also be found in bile, plasma, and other epididymal fluids). The accumulation of cholesterol was greatly reduced when the //NPC2-/-// mice were given the replacement enzyme (Figure 7); however, the accumulation of cholesterol is not completely reversed. The liver of the //NPC2-/-// mice’s cholesterol levels dropped approximately 6-fold (from a 12-fold accumulation) and a 2.6-fold decrease in the lungs’ cholesterol levels. In contrast, the brain cholesterol levels were less affected by the NPC2 enzyme replacement. There were minimal changes in cholesterol accumulation in the cerebellum and cerebral cortex, and no reduction of cholesterol accumulation in the hippocampus. Another drawback is that the neurological symptoms are not stopped by the ERT; the //NPC2-/-// mice experienced tremors and degenerating motor skills rapidly after 8-weeks on the ETR.

A very recent discovery and paper by Aqul //et al//. provides evidence that a minute injection of 2-hydroxypropyl- β-cyclodextrin (CD) can delay neurodegeneration and increase the patient’s life expectancy. Peake K.B. and Vance J.E. further investigated the implications of the CD injection on cholesterol levels, and neuron and astrocyte (glial cells) vitality in //NPC1-/-// mice. They determined that 0.1 mM CD reduced cholesterol synthesis and increased its metabolism; whereas 1 mM CD increased the rate of lipid synthesis and overall was preventing cholesterol exocytosis. Using the mice as their models, the researchers calculated that approximately 0.5 mg/Kg (CD/body weight) was sufficient to sustain cholesterol metabolism for more than 6 days. They also suggested directly injecting both the liver and the brain; the blood-brain barrier allows only 0.2% of the CD to enter the brain and this is not a sufficient amount.

4.2b Stem Cells to Replace Brain Tissue
Lee, J.M. //et al//. used multipotential neural stem cells to reverse the neurological effects of NPC in the cerebellum, which include the accumulation of cholesterol and the degeneration of neural pathways. The MHP36 (conditionally immortalized neural stem cells) acts by protecting Purkinje neurons and promoting the formation of functional synapses in the cerebellum. They determined that MHP36 could be a viable therapy for Niemann-Pick Disease patients, where it will protect the Purkinje neurons with no immunological response that would work against the treatment. One complication is that the MHP36 stem cells do not live longer than 4 weeks, but the other symptoms (e.g. lipid accumulation) were down regulated and there was an improvement in motor function.

=5. Other Related Links= =6. References=
 * The Canadian Chapter of the National Niemann-Pick Disease Foundation
 * National (US) Institute of Neurological Disorders and Stroke - Niemann-Pick Disease
 * [|Niemann-Pick Disease Type C (NCBI Bookshelf)]