Smith-Magenis syndrome (SMS) is characterized by distinctive facial features, developmental delay, cognitive impairment, and behavioral abnormalities, which includes significant sleep disturbance, maladaptive and sometimes violent self-injurious behaviors. The diagnosis is confirmed either by detection of an gene deletion of the short arm of chromosome 17 band p11.2, or by molecular genetic testing of RAI1, Almost all cases of SMS occur by chance and are not inherited.
Hereditary hemorrhagic telangiectasia (HHT) is characterized by the presence of multiple arteriovenous malformations (AVMs) , direct connections between arteries and veins without the usual intervening capillaries. The most common sympton is spontaneous frequent nosebleeds. Other type of spontanious bleeding in the brain, lungs, or gastrointestinal tract can occur; complications from bleeding or shunting may be sudden and catastrophic. HHT is inherited in an autosomal dominant manner and most individuals have an affected parent. HHT is caused by a mutation in either ENG, the gene encoding endoglin or ACVRL1, the gene encoding the activin receptor.
Batten disease is the most common neuronal ceroid-lipofuscinoses (NCLs). NCLs are a group of inherited, neurodegenerative, lysosomal-storage disorders characterized by progressive mental and motor deterioration, seizures, and early death. Six genes — PPT1, CLN2, CLN3, CLN5, CLN6, and CLN8 — cause NCL. The NCLs are usually inherited in an autosomal recessive manner.