NCBI Bookshelf. Faisal Akhtar ; Syed Rizwan A. Bokhari 2. Down syndrome was first described by an English physician John Langdon Down in , but its association with chromosome 21 was established almost years later by Dr. Jerome Lejeune in Paris. The majority of patients with Down syndrome have an extra copy of chromosome
This page has been archived and is no longer updated. Currently, Down syndrome DS is one of the most common birth defects , affecting about one in every live births. John Langdon Down first described this condition in the medical literature in , documenting the various symptoms associated with the syndrome but failing to determine their cause. In fact, the cause of DS remained unknown for nearly years following Down's work. Then, in the s, researchers finally determined the source of DS: the presence of an extra copy of chromosome 21, a condition often referred to as trisomy
What causes chromosome disorders? What is an autosomal dominant disorder? What is an autosomal recessive disorder?