18p deletions FTNW - Unique - The Rare Chromosome Disorder ...

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Results of the chromosome test Your geneticist or genetic counsellor will be able to tell you about the point where the chromosome has broken in your child. You will almost certainly be given a karyotype which is shorthand notation for their chromosome make-up. With an 18p deletion, the results are likely to read something like the following example: 46, XY, del(18)(p11.2) 46 The total number of chromosomes in your child’s cells XY The two sex chromosomes, XY for males; XX for females del A deletion, or material is missing (18) The deletion is from chromosome 18 (p11.2) The chromosome has one breakpoint in band 18p11.2, and material from this position to the end of the chromosome is missing In addition to, or instead of a karyotype you may be given the results of molecular analysis such as cytogenetic fluorescent in situ hybridisation (FISH) or microarrays (array -CGH) for your child. In this case the results are likely to read something like the following example: 46,XX.ish del(18)(p11.3)(D18S552-)de novo 46 The total number of chromosomes in your child’s cells XX The two sex chromosomes, XY for males; XX for females .ish The analysis was by FISH (fluorescent in situ hybridisation) del A deletion, or material is missing (18) The deletion is from chromosome 18 (p11.3) The chromosome has one breakpoint in band 18p11.3, and material from this position to the end of the chromosome is missing. (D18S552-) The deleted part of chromosome 18 includes a stretch of DNA termed D18S552 de novo The parents’ chromosomes have been checked and no deletion or other chromosome change has been found at 18p11.3. The deletion is very unlikely to be inherited and has almost certainly occurred for the first time in this family with this child arr[hg19] 18p11.32p11.21(2,120-15,227,370 )x1 arr The analysis was by array-CGH hg19 Human Genome build 19. This is the reference DNA sequence that the base pair numbers refer to. As more information about the human genome is found, new “builds” of the genome are made and the base pair numbers may be adjusted 18p11.32p11.21 Chromosome 18 has two breakpoints, one in the band 18p11.32, and one in band 18p11.21 (2,120-15,227,370 ) The base pairs between 2,120 and 15,227,370 have been shown to be deleted. Take the first long number from the second and you get 15,225,250 (15.2Mb). This is the number of base pairs that are deleted x1 means there is one copy of these base pairs, not two – one on each chromosome 18 – as you would normally expect . 4
Are there people with an 18p deletion who are healthy, have no major medical problems or birth defects and have developed normally? Yes. In a few people, a deletion appears to have only a mild effect. A Unique mother with an 18p deletion has no problems due to the deletion, while her baby who inherited the deletion was severely affected and died. There are also reports in the literature of individuals who are only mildly affected. One reports a 26-year-old woman with borderline learning difficulties who is small (below the 25 th centile for height and weight) but has no major medical concerns. Another describes a mother who had two children who also had 18p-. This mother was small and had some of the facial features of 18p- (high palate, misaligned teeth, a small mouth with a receding chin) but was otherwise little affected. A 34-year-old man is described as having normal growth and psychomotor development. He had ptosis (drooping of the upper eyelids) which was surgically corrected as a child; he also has severe tooth decay and clinodactyly of the fifth finger. Developmental testing at age 6 revealed no problems and he attended normal school and lives independently, working in a factory. All of these individuals are thought to have a non-mosaic deletion of 18p, that is, the 18p deletion is present in all the cells. A mosaic deletion of 18p is where the deletion is only present in some, not all, of the cells (Tonk and Krishna 1997, Rigola 2001, Maranda 2006, Unique). What is the outlook? The outlook for any baby or child depends on how the deletion has disrupted early development in the womb. The most significant medical concern that can affect lifespan is holoprosencephaly, a brain defect that is sometimes seen in individuals with 18p-. For those not affected in this way, life expectancy is normal and there are many healthy older teenagers and adults with deletions of 18p (see Adults with 18p-). She leads a relatively normal life and is a happy confident girl with a bright future. 10½ years Growing up with an 18p deletion: 1 year 3 years 6 years 5
Page 1 and 2: 18p deletions rarechromo.org
Page 3: Looking at 18p Chromosomes can’t
Page 7 and 8: After birth, babies tend to grow mo
Page 9 and 10: Speech and communication Speech app
Page 11 and 12: Development: hand-eye co-ordination
Page 13 and 14: Medical concerns • Brain A handfu
Page 15 and 16: • Hands Hands can also be affecte
Page 17 and 18: • Tonsils The Unique survey revea
Page 19 and 20: He has a lovely nature and is very
Page 21 and 22: Correlation between the breakpoints
Page 23 and 24: Can it happen again? The possibilit

18p deletions FTNW - Unique - The Rare Chromosome Disorder ...

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