RARE BIRTH DEFECTS: A birth defect is a health condition that is present at birth. Birth defects may change the shape or function of one or more parts of the body. They can cause problems in overall health, how the body develops, or how the body works. One in 33 babies in the United States is born with a birth defect. We don’t know the cause of all birth defects. Some may be caused by the genes we inherit from our parents. Others may be caused by environmental factors, like exposure to harmful chemicals. Some may be caused by a combination of genes and environment. In most cases, the causes are unknown. What are rare birth defects? There are thousands of different birth defects. The most common are heart defects, cleft lip and palate, Down syndrome and spina bifida. Others, such as the ones listed below, are rare and less well known. Use the links to find out more information about these birth defects. Or visit the Office of Rare Disease Research or Genetics Home Reference. Rare birth defects include: 22q11.2 deletion syndrome (DiGeorge Syndrome and Velocardiofacial syndrome)Albinism, ocularAlbinism, oculocutaneousAnencephaly (a neural tube defect)Arnold-Chiari malformation (chiari malformation)CHARGE syndromeCongenital adrenal hyperplasiaCongenital diaphragmatic hernia (CDH)Congenital hydrocephalusCraniosynostosisDandy Walker malformationEhlers Danlos syndromeEpidermolysis bullosaGorham's diseaseHashimoto's syndrome (autoimmune thyroiditis)Hydrops fetalis (immune and nonimmune)HypotoniaKlippel-Feil syndromeMuscular dystrophyOsteogenesis imperfectaProgeriaSmith Lemli Opitz syndromeSpinal muscular atrophyTuberous sclerosisTurner syndromeX-linked lymphoproliferative syndrome (Duncan disease)