Everyone has 23 pairs of chromosomes, numbered from 1 to 22 plus the x and y chromosomes.
Each section of each chromosome is numbered to make up a cytogenic map, which is created by distinctive bands visable when chromosomes are stained with certain chemicals.
Chromosome 3 looks like this
Imogen is missing 3P25.3-26.3 the very end of the chromosome. This defines her deletion as terminal (meaning the end of the chromosome, not that its deadly!)
Each of us has roughly 20,000 genes and probably around 400 genetic or chromosomal changes that might make us more prone to a certain illness, have a certain quirk, or may have no effect at all.
However, when a large chunk of chromosome is deleted this can have catastrophic effects. Imogen’s deletion is 10.7mb which is a pretty large amount. It contains 99 genes that she has only one copy of instead of two.
Each person with a 3p25 deletion is unique and will have different developmental and medical concerns. No one person will have all of the features listed in this guide – even if their chromosome deletion appears to be exactly the same. However, a number of common/possible features have emerged, and effected individuals will have some of the below list.
- Low birth weight. Most children also grow slowly and remain short
- Feeding problems – many 3p25 babies will be tube fed, and will have problems weaning
- Delay in reaching baby ‘milestones’ and later developmental delay, most will eventually meet physical milestones such as sitting and walking but will be late in doing so, and many will remain non verbal, although some do talk, and others may sign or use augmented speech.
- Hypotonia – floppiness
- Need for support with learning
- Ptosis – an inability to fully raise the upper eyelid (extremely common)
- Unusual facial features, such as wide-spaced eyes, low set ears, and a long groove between the nose and upper lip
- Small head (microcephaly). The head is sometimes an unusual shape
- Autism and challenging behaviour
- Cleft palate or other palate anomalies
- Extra fingers and/ or toes
- Dimple near the base of the spine
- Bowel or intestinal problems
- Seizures (1 in 3 chance)
- Hearing impairment, temporary in some children
- Kidney problems
- Heart conditions
- Pits/ tiny holes in the cheek just in front of the ears
- Scoliosis or other mild skeletal problems
(Cargile 2002; Malmgren 2007; Fernandez 2008; Shuib 2009; Pohjola 2010; Unique).
3p25 deletion is incredibly rare, around 50 cases have been recorded in the last 30 years. A crude estimate by myself puts it at around 1 in 500,000 births. But as genetics have come on considerably in the last 5 years and will continue to do so, I would imagine diagnosis numbers will grow.
Each chromosome disorder is in it self very rare, however collectively babies born with rare chromosome disorders of any sort is about 1 in 200 so a lot more common then you might expect! And that doesn’t include the more known chromosome disorder such as Down Syndrome.
Chromosome deletions can be passed on from parents, or can be a completely random occurrence as Imogen’s is. This means it hasn’t been passed from either of the parents, it is ‘De novo’.
For a detailed explanation of 3p25 read Unique’s PDF.