Chromosome Disorders

Chromosome Disorders

·        Polyploidy: duplication of whole sets of chromosomes (eg triploidy: n = 69). Non-survivable ® fetal wastage

·        Anuploidy:

o   One missing or additional chromosome

o   Trisomy 21: 47XY + 21. 

o   Trisomy 13: next most common, trisomy

o   Turner‟s Syndrome: 45, XO

§  Puffy feet, poor toe nails, redundant skin behind head/neck, kidney and cardiac malformation

§  Later: short, infertile, normal mental ability (unless 2^nd X ring chromosome ® mental disability)

§  The 10% that survive to term are the good end of the spectrum

§  Differential: Noonan‟s Syndrome – similar symptoms but karyotype is normal

o   Klinefelter Syndrome: 47, XXY

§  1/3 present in childhood with learning difficulty

§  1/3 present in adolescent: failure of puberty due to no testosterone (ie hypogonadism)

§  1/3 present in adulthood due to infertility

·        Chromosome abnormalities:

o   Deletions, insertions, etc. Will be different in each child ® variable presentation. Eg deletion in 5p: Cri du Chat syndrome, cat like cry

o   Fragile X Syndrome: commonest cause of mental disability in males.  1:1,000

·        In testing for mosaics, may need to test skin, not blood, as abnormal cells don‟t reproduce so well so get weeded out in tissues (eg blood) with high turnover