Severe combined immunodeficiency (SCID) is an inherited disorder of the immune system resulting from a defect in both T and B lymphocytes. Beginning in the first few months of life, affected individuals are prone to recurrent and persistent infections caused by opportunistic bacteria, viruses, and fungi. These infections are often serious or life-threatening. Researchers have described several different types of severe combined immunodeficiency, which are caused by mutations in multiple genes.

Fabry disease is an inherited disorder that results from the buildup of a fatty substance called globotriaosylceramide in the body's cells. This buildup leads to episodes of pain, particularly in the hands and feet; small, dark red spots on the skin called angiokeratomas; decreased sweating (hypohidrosis); corneal opacity; and hearing loss. Fabry disease can also involve potentially life-threatening complications such as progressive kidney damage, heart attack, and stroke. This disorder is caused by mutations in the GLA gene; it has an X-linked pattern of inheritance.

Pompe disease is an inherited disorder caused by the buildup of a complex sugar called glycogen in the body's cells. The accumulation of glycogen in certain organs and tissues, especially in muscles, impairs their ability to function normally. Major features of Pompe disease include muscle weakness, heart abnormalities, and breathing problems. This disorder is caused by mutations in the GAA gene; it has an autosomal recessive pattern of inheritance.

Krabbe disease is an inherited disorder that affects the nervous system. This condition is characterized by severe muscle weakness, slow mental and physical development, vision loss, and seizures. Mutations in the GALC gene cause Krabbe disease; it has an autosomal recessive pattern of inheritance.

Gaucher disease is an inherited disorder that affects many of the body's organs and tissues. Common signs and symptoms include hepatosplenomegaly, anemia, thrombocytopenia, lung disease, and bone abnormalities. The severe types of the disease also involve the central nervous system, causing neurological problems such as abnormal eye movements, seizures, and brain damage. Gaucher disease results from mutations in the GBA gene; it has an autosomal recessive pattern of inheritance.

Niemann-Pick disease is an inherited disorder in which the body in unable to process fats and cholesterol properly. People with this condition have some combination of the following features: failure to thrive, an enlarged liver and spleen, neurological problems, frequent lung infections, an increased risk of abnormal blood clots, developmental delay, seizures, and poor muscle tone. Mutations in the SMPD1 gene causes Niemann-Pick disease; it has an autosomal recessive pattern of inheritance.

Critical congenital heart disease (CCHD) is a term that refers to a group of serious heart defects that are present from birth. These abnormalities result from problems with the formation of one or more parts of the heart during the early stages of embryonic development. CCHD prevents the heart from pumping blood effectively or reduces the amount of oxygen in the blood. As a result, organs and tissues throughout the body do not receive enough oxygen, which can lead to organ damage and life-threatening complications. Individuals with CCHD usually require surgery soon after birth.