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Definition Niemann-Pick disease (NPD) is a group of inherited metabolic disorders in which harmful quantities of a fatty substance (lipids) accumulate in the spleen, liver, lungs, bone marrow, and brain. There is a deficiency of a lysosomal enzyme called acid sphingomyelinase or disturbance in cholesterol breakdown or transportation. This enzyme …

Definition Norovirus infection is the most common cause of infection in gastrointestinal outbreaks. It causes sudden onset of nausea, vomiting, and diarrhea.  Sometimes it may also cause stomach cramping. In addition, the person may feel tired, muscle ache, headache, and low-grade fever. Norovirus is a very contagious virus that can …

Definition Nephrotic syndrome is the state that the kidney excretes large amounts of protein in the urine. It is usually caused due to the damage in the cluster of blood vessels in the kidney that filters waste materials from the blood. It causes swelling (edema) in ankles, legs and feet. …

What is night blindness? Night blindness (Nyctalopia) is the inability to see well at night or in poor light. It is not a disease in itself, but rather a symptom of an underlying problem, usually a retina problem. It is common for patients who are myopic to have some difficulties …

Definition Nocardiosis is a rare infection caused by the Nocardia asteroides bacterium. This type of bacteria can be found in the soil and water of regions around the world. People may become infected with this bacteria when they inhale it or when the bacteria enter an open wound. The infection …

Definition Neurofibromatosis is a genetic disorder that causes tumors to form on nerve tissue. These tumors can develop anywhere in your nervous system, including your brain, spinal cord and nerves. Neurofibromatosis is usually diagnosed in childhood or early adulthood. Neurofibromatosis Types of Neurofibromatosis The three types of neurofibromatosis are Nf1, …

Definition Noonan’s syndrome is a genetic disorder that prevents normal development in various parts of the body. A person can be affected by Noonan syndrome in a wide variety of ways. These include unusual facial characteristics, short stature, heart defects, other physical problems and possible developmental delays. Noonan’s syndrome History …

Definition Narcolepsy is a chronic sleep disorder characterized by overwhelming daytime drowsiness and sudden attacks of sleep. People with narcolepsy often find it difficult to stay awake for long periods of time, regardless of the circumstances. Narcolepsy can cause serious disruptions in your daily routine. Sometimes, narcolepsy can be accompanied …