Diseases That Run in Families
What?
Diseases that run in families are also known as inherited diseases. Some of these have clear genetic causes – and are the result of a specific gene mutation that is inherited in a specific way – others have more complicated causes, including a combination of genetic and environmental reasons.
Many inherited diseases are also rare diseases, meaning they occur in less than 200,000 people in the US.
Inheritance patterns
Diseases that run in families may be inherited in several ways.
Some of the main types of inheritance patterns include:
Autosomal recessive and autosomal dominant inheritance are the most common. When it comes to autosomal recessive disease, a disease is inherited by the passing down of one copy of a gene mutation from each parent. The individual inheriting the disease receives two copies of a mutated gene. With autosomal dominant inheritance, just one copy of the gene mutation passed down from one parent is enough to trigger a rare disease in an offspring.
Other modes of inheritance include X-linked inheritance, where gene mutations are passed down on the inherited X sex chromosomes. Mitochondrial inheritance which is passed from the Mother only. Chromosomal deletions may also be inherited and trigger inherited diseases. Another form of inheritance is disomy, when instead of receiving one copy of each chromosome pair from both parents, an individual receives both copies of a chromosome pair from one parent.
Rare diseases
*These diseases are listed in alphabetical order and represent just a sample of some of the rare diseases that can run in families.
22q11.2 deletion syndrome (DiGeorge)
Symptoms of this rare inherited disease vary widely among individuals, and even amongst family members with the same diagnosis. It occurs in around 1 in every 4,000 births in the US, and is recognized as a microdeletion syndrome passed down through families in an autosomal dominant pattern. A parent who carries one of the many gene mutations responsible for this inherited disease has a 50% chance of their child being diagnosed with the syndrome.
This rare disease can run in families according to an autosomal dominant or autosomal recessive pattern of inheritance. Multiple gene mutations are responsible for the syndrome, and the mode of inheritance is dependent on the type of gene affected. Symptoms of this inherited disease include issues that affect the limbs, scalp and skin of those affected.
This inherited disease is the result of one confirmed gene change, and one further gene mutation which is under investigation as a cause of this rare syndrome. CHARGE syndrome is an example of an inherited disease that may be inherited (in an autosomal dominant pattern) or it may be the result of a de novo, or new gene change.
Many rare diseases may be inherited and consequently run in families. However some, when they occur, are the first instance in a family and the result of a de novo or new mutation. This new mutation will then create a new pattern of inheritance within a family.
Genetic counseling
Understanding how diseases run in families is complicated. Sometimes the precise ways in which a rare disease is inherited are not known. Genetic counseling is an important education and support service which can help individuals and families understand more about how and why diseases run in families, and if genetic testing is required to identify a specific genetic syndrome within a family.
