From NCBI curation
Hypertrophic cardiomyopathy (HCM) is typically defined by the presence of unexplained left ventricular hypertrophy (LVH). Such LVH occurs in a non-dilated ventricle in the absence of other cardiac or systemic disease capable of producing the observed magnitude of increased LV wall thickness, such as pressure overload (e.g., long-standing hypertension, aortic stenosis) or storage/infiltrative disorders (e.g., Fabry disease, amyloidosis). The clinical manifestations of HCM range from asymptomatic LVH to progressive heart failure to sudden cardiac death (SCD), and vary from individual to individual even within the same family. Common symptoms include shortness of breath (particularly with exertion), chest pain, palpitations, orthostasis, presyncope, and syncope. Most often the LVH of HCM becomes apparent during adolescence or young adulthood, although it may also develop late in life, in infancy, or in childhood.

From MedlinePlus Genetics
Nonfamilial hypertrophic cardiomyopathy tends to be milder. This form typically begins later in life than familial hypertrophic cardiomyopathy, and affected individuals have a lower risk of serious cardiac events and sudden death than people with the familial form.

The symptoms of familial hypertrophic cardiomyopathy are variable, even within the same family. Many affected individuals have no symptoms. Other people with familial hypertrophic cardiomyopathy may experience chest pain; shortness of breath, especially with physical exertion; a sensation of fluttering or pounding in the chest (palpitations); lightheadedness; dizziness; and fainting.

In familial hypertrophic cardiomyopathy, cardiac thickening usually occurs in the interventricular septum, which is the muscular wall that separates the lower left chamber of the heart (the left ventricle) from the lower right chamber (the right ventricle). In some people, thickening of the interventricular septum impedes the flow of oxygen-rich blood from the heart, which may lead to an abnormal heart sound during a heartbeat (heart murmur) and other signs and symptoms of the condition. Other affected individuals do not have physical obstruction of blood flow, but the pumping of blood is less efficient, which can also lead to symptoms of the condition. Familial hypertrophic cardiomyopathy often begins in adolescence or young adulthood, although it can develop at any time throughout life.

While most people with familial hypertrophic cardiomyopathy are symptom-free or have only mild symptoms, this condition can have serious consequences. It can cause abnormal heart rhythms (arrhythmias) that may be life threatening. People with familial hypertrophic cardiomyopathy have an increased risk of sudden death, even if they have no other symptoms of the condition. A small number of affected individuals develop potentially fatal heart failure, which may require heart transplantation.

Hypertrophic cardiomyopathy is a heart condition characterized by thickening (hypertrophy) of the heart (cardiac) muscle. When multiple members of a family have the condition, it is known as familial hypertrophic cardiomyopathy. Hypertrophic cardiomyopathy also occurs in people with no family history; these cases are considered nonfamilial hypertrophic cardiomyopathy.   https://medlineplus.gov/genetics/condition/familial-hypertrophic-cardiomyopathy