Jacobsen syndrome is a rare chromosomal disorder resulting from deletion of genes from chromosome 11 that includes band 11q24.1. It is a congenital disorder. Since the deletion takes place on the q arm of chromosome 11, it is also called 11q terminal deletion disorder. The deletion may range from 5 million to 16 million deleted DNA base pairs. The severity of symptoms depends on the number of deletions; the more deletions there are, the more severe the symptoms are likely to be. People with Jacobsen syndrome have serious intellectual disabilities, dysmorphic features, delayed development and a variety of physical problems including heart defects. Research shows that almost 88.5% of people with Jacobsen syndrome have a bleeding disorder called Paris-Trousseau syndrome. Jacobsen syndrome is catastrophic in 1 out of every 5 cases, with children usually dying within the first 2 years of life due to heart complications. Signs and symptoms Almost all children with Jacobsen syndrome have intellectual disabilities, which range from mild to moderate depending upon the number of the deletions of genes from the chromosome. Most have delayed development, including delayed speech, motor disabilities and lack of coordination, which makes simple activities like sitting, standing and walking difficult. Most children eventually start speaking, but in cases with severe intellectual disability language use is highly restricted. They have distinctive facial features like: Small head (microcephaly) Pointed forehead (trigonocephaly) Small ears which are low-set Widely-spaced eyes (hypertelorism) Droopy eyelids (ptosis) Broad nasal bridge Abnormally thin upper lips Downturned corners of the mouth Excess skin covering in the inner corner of eyes (epicanthal folds) Some children also experience behavioural problems like distractibility, hyperactivity, impaired communication and social skills, which qualifies them for a diagnosis of ASD and ADHD. Heart defects are very common in children with Jacobsen syndrome. 88.5% of people with the disorder have Paris-Trousseau syndrome, which is a bleeding disorder and causes a lifelong risk of abnormal bleeding and bruising due to dysfunction in the platelets. Other symptoms may include eye problems, ear and sinus infections, hearing problems, bone deformities, growth hormone deficiency, gastrointestinal problems, kidney malfunctions, etc. Cause Jacobsen syndrome is caused by deletion of genetic material from the long arm of chromosome 11. The size of deletion may vary across patients, but the deletion always occurs at the end terminal of the q arm of chromosome 11. There are three ways in which the deletion could occur: de