Ring 18 rarechromo.org Sources Ring 18 The information in Ring 18 Syndrome is a rare genetic condition caused by this leaflet comes having an unusual chromosome. from the medical What is a chromosome? literature and a The human body is made up of cells. Inside most cells is survey of family a nucleus where genetic information is stored in genes members of which are packaged into chromosomes. Unique . Unique is Chromosomes are large enough to be studied under a very grateful to microscope and come in different sizes, each with a top the families who (short) arm called p and a bottom (long) arm called q. took part in the They are numbered from largest to smallest according survey. to their size, from number 1 to number 22, in addition The medical to the sex chromosomes, X and Y. A normal, healthy literature largely cell in the body has 46 chromosomes, 23 from the contains mother and 23 from the father, including one descriptions of chromosome 18 from each parent. people with Ring In people with Ring 18, the ends of one chromosome 18 written by 18 have joined up to form a circle. When this happens, doctors to help genes are usually lost from either the p arm or the q other doctors arm or both, and it is presumed that these missing make accurate genes cause most of the signs of Ring 18 Syndrome. diagnoses. Some of the features they Most people with Ring 18 have the ring chromosome in mention, such as all their body cells. Some people have some cells with odd-shaped ears, the ring chromosome and some with normal cells. This are not very is called mosaicism and your geneticist will tell you if important to this is what your child has. The effects of the ring are parents or to their less easy to predict in someone with mosaicism but child. Very obvious they can be milder (Fryns 1992; Stankiewicz 2001). or extreme problems such as club feet or heart conditions are more likely to be mentioned and this can create a picture that is unnecessarily gloomy. No one knows how many Ring chromosome 18 people there are with Ring 18 who never come to doctors’ attention. 2 Main features References People with Ring 18 differ a lot from each other and while The text contains some people appear completely unremarkable, others are references to more severely affected. You will find here lists of ‘typical’ articles published in features. Most people have features of 18q- (having lost the medical press. material from the end of the long arm), some have The first-named features of 18p- (having lost material from the short arm) author and and some have a mixture. Your child will not have all of publication date are the typical features or even most of them but he or she given to allow you will almost certainly have some (Stankiewicz 2001). to search for the Features more common in people who have abstracts or original articles on the lost the end of 18q (18q-) internet in PubMed. • Very narrow or closed ear canals, usually with If you wish, you can hearing loss. Ears may be abnormally formed, with a obtain abstracts and prominent antihelix (see below, right). key articles from • Unusual feet: including features such as rocker bottom Unique . Information feet (with a convex sole, without an instep or arch), from the Unique abnormal or overriding 2nd and 3rd toes, talipes (club survey is marked foot). (U). • Congenital heart defect. • Unusual hands: including features such as tapering Supernumerary th fingers, low set thumbs, incurving little (5 ) fingers. Ring 18 • In boys, minor genital abnormalities, such as the hole There is an at the end of the penis being on the underside extremely rare type (hypospadias). of Ring 18 that • Increased chance of developing juvenile rheumatoid occurs when a arthritis. This causes inflamed and stiff joints. third, extra Features more common in people who have chromosome 18 is present as a ring. lost the end of 18p (18p-) This is called • Difficulty resisting infections. supernumerary Ring • Holoprosencephaly. This is a developmental defect 18 and the features that occurs when the brain and face are forming. The are different to forebrain does not grow forward and divide into two those of the Ring hemispheres as it is supposed to do. The severity 18 disorder varies, with the least affected people having some described in this fused structures and the most severely affected having leaflet. helix a single brain mass instead of two separate lobes. Most people come between these two extremes. The middle of the face is often affected as well: one of the mildest effects can be the growth of a single front tooth; one of the most severe, a single eye. antihelix 3 How • Small jaw (micrognathia). common is • Tooth decay. • Ptosis (drooping of upper eyelids). Ring 18? Ring 18 is rare Features common in people who have lost but no-one can either end of chromosome 18 be certain how • Delayed development. uncommon it is • Some degree of learning difficulty. because a few • Floppy muscles (low muscle tone, hypotonia). people have the • disorder Failure to thrive (difficulty putting on weight and without obvious growing). • symptoms. Short stature with a shortage of growth hormone. • Around 70 Small head and brain (microcephaly). people have • Skin folds across the inner corners of the eyes been described (epicanthal folds). in the medical • Abnormalities of the roof of the mouth (palate). literature and the Other features Chromosome Many other unusual features have been described in 18 Registry people who have lost material from the ends of knows of more chromosome 18. However, not enough people have been than 120 described yet to be certain that these features are caused people. by loss from chromosome 18 or Ring 18 Syndrome. Out of 82,000 Experiences of pregnancy people whose A small group of 12 families have told us about their chromosomes pregnancy experiences. They are varied but the largest were number of mothers carrying babies with Ring 18 investigated at a experienced no pregnancy problems and only discovered major European that their baby was affected after the birth. Four babies genetics centre, were small for dates and two mothers had a low level of ten had a Ring amniotic fluid. One mother had excess amniotic fluid and 18 (Fryns 1992; two babies were induced two to three weeks after their Schinzel 2001). due date. Other experiences may have no link with Ring 18: one mother had a high cholesterol level while pregnant, one mother was carrying twins but lost one, one mother had pancreatitis (inflammation of the pancreas) during pregnancy and had her gallbladder removed (U). Newborn experiences Out of 10 families who told us about their baby’s experiences as a newborn, seven had feeding difficulties, 4 with a poor sucking reflex and failure to put on weight. Two babies developed neonatal jaundice and two others were very floppy. Two babies developed severe infections while still in hospital, in one case affecting the stump of the umbilical cord, followed by an RSV (respiratory syncytial virus) infection (U). First signs Of 11 families who told us what the first signs were that anything was wrong with their baby, four were healthy and looked quite normal at birth but were slow to reach their developmental milestones. Five other babies had obvious signs at birth – one was very small for dates, two had a cleft palate and two had club feet (talipes). One baby was diagnosed after she developed seizures at four months and one after a severe infection. All babies were diagnosed before their first birthday (U). Diagnosis Ring 18 is diagnosed by examining the chromosomes in white blood cells. The ring chromosome is obvious under a microscope but molecular genetic tests are needed to discover more precisely how much material and which genes are missing. Laboratories offer different molecular tests including FISH ( a technique called chromosome painting) using whole and partial chromosome 18 paints (Stankiewicz 2001). Appearance Most children – typically four children out of five - are very short compared with other family members. If they do not have other obvious problems such as a cleft lip, ptosis (a drooping upper eyelid) or talipes, they may look little different to other children and even if they do, after surgery there is usually little, if anything, to see of the original problem. Even problems that some think of as cosmetic can be corrected surgically. Some, such as the fine, curly and fair hair that some children with Ring 18 have, can just be admired. Growth People with Ring 18 are generally short as children and become short adults. Without treatment, predicted adult height is around five foot (150cm). 5 Birth statistics recorded at Unique suggest that the Families growth delay does not start in all babies before birth. say … Among boys, the range of birth weights was between the 9th and 70 th centiles on the standard child growth chart Tatum has been on and the range of birth weights for girls was very similar. growth hormone At around 18 to 20 inches (46 to 51 cm), birth lengths since she was 11 were generally around or slightly below average but months old and within the normal range. has done After birth, babies tend to grow slowly and it has been wonderfully. She suggested that losing one or more genes from the long caught up in height arm of chromosome 18 at 18q23 may be one cause of the and weight at first growth failure although other, as yet unknown, factors and it also helped also play a role.