Cells and Genes Flashcards
What is Lyonisation?
The process of X-inactivation.
Females transcriptionally silence one of their two Xs. The inactivated X chromosome, then condenses into a compact structure called a Barr body, which is maintained in a silent state.
The process of X-inactivation is random. There is no preference for the inactivation of paternal or maternal X chromosomes. It occurs very early in embryogenesis, soon after the fertilization of the egg by the sperm.
It occurs in all somatic cells of women.
Name the three types of aneuploidy that survive birth
- Trisomy 21 (Down’s syndrome) - 1 in 800 births
- Trisomy 18 (Edwards syndrome) - 1 in 6000 births
- Trisomy 13 ( Patau syndrome) - 1 in 10000 births
What are the features of Kleinfelter’s syndrome (XXY)?
Considerable variability. Many remain undiagnosed.
May have low testosterone, infertility (most but not all), speech and language issues and intellectual disability. More likely to be timid and unassertive (but usually no major issues with social interaction). Issues become more evident in puberty. Tend to be tall with long legs and small testes. Behavioural issues are not uncommon.
What are the features of XYY syndrome?
Considerable variability. Many remain undiagnosed.
Intellectual disability is not the norm but some degree of speech and language / educational issue is not uncommon. May be taller than expected. Normal sexual development and fertility is expected (although infertility can occur). Low set ears are associated.
What are the features of triple X syndrome?
Considerable variability, Many remain undiagnosed.
May have no features. May appear taller than average. Often global developmental delay and intellectual disability. Most have normal sexual development and can conceive children.
What are the features of Turner syndrome (X monosomy)?
Varies widely, short stature (usually apparent by age 5), webbed neck, widely spaced nipples. Absent periods and incomplete breast development are common. Most affected are infertile (although assisted reproduction is an option). Intelligence tends to be normal although rates of intellectual disability are increased.
What are the features of Edwards syndrome (trisomy 18)?
Severe intellectual disability, babies often die soon after birth. Kidney malformations, upturned nose, webbing of second and third toes, and clubbed feet (rocker bottom).
What are the features of Patau syndrome (Trisomy 13)?
Severe intellectual disability, babies often die soon after birth. Most have congenital heart malformations, anophthalmia and a cleft palate.
What conditions are related to 22q11 Deletion Syndrome?
DiGeorge Syndrome/Velocardiofacial Syndrome
Which condition is caused by a deletion in the short arm of chromosome 5?
Cri-du-chat syndrome
Which condition is caused by a deletion in the long arm of chromosome 15?
Prada-Willi syndrome (paternal microdeletion) and Angelman syndrome (maternal microdeletion)
Autism spectrum disorder is associated with abnormalities in which chromosome?
Chromosome 2, 7, 16, 19
What are the features of Angelman (Happy puppet) syndrome?
15q11 maternal origin
Flapping hand movements (uplifted, flexed arms when walking), ataxia, pronounced verbal delay (compared to comprehension), severe to profound learning disability, seizures and sleep problems
What are the features of Prada-Willi syndrome?
15q11 paternal origin
Hyperphagia, excessive weight gain, short stature, frequent skin picking, mild learning disability, small gonads, and hypotonia
What are the features of Cri du chat?
5p deletion
Characteristic cry like a meowing kitten, hypotonia, hypertelorism, a down-turned mouth, and microcephaly
What are the features of Velocardiofacial (Di George) syndrome?
22q (deletion)
Cleft palate, cardiac problems, and learning disabilities. A higher rate of psychiatric disorders is also seen
What are the features of Lesch-Nyhan syndrome?
Xq26-27
Self mutilation, dystonia and writhing movements
What are the features of Smith-Magenis syndrome?
17p11
Pronounced self injurious behaviour, self hugging, and a hoarse voice
What are the features of Fragile X?
Elongated face, large ears, large testicles, hand flapping, shyness, and little eye contact
What are the features of Wolf Hirschhorn syndrome?
4p
Mild to severe intellectual disability (majority are severe), severe growth delay, microcephaly, seizures, down turned fishlike mouth, Greek warrior helmet face, and cleft lip
What are the features of Rett syndrome?
Normal for the first 12 months. Regression and loss of skills from around 18 months onwards. Hand-wringing movements are the most common feature. Associated learning disability is profound. Affects girls almost exclusively
What are the features of Williams syndrome?
7q11 deletion
Elfin like features, social disinhibition, and abnormal friendliness towards strangers. Very sensitive hearing is also seen. Advanced verbal skills, speech is articulate but superficial (referred to as cocktail party speech). Cardiac issues (most common being supravalvular Aortic Stenosis).
What is the role of astrocytes?
A type of macroglia that provide structural and metabolic support to neurons, ensuring that synapses function properly.
- Nutrient supply
- Neurotransmitter recycling
- Blood brain barrier support
- Homeostasis
What are the two main types of astrocytes?
Protoplasmic Astrocytes: Found in grey matter, they interact extensively with synapses and support neuronal function.
Fibrous Astrocytes: Predominant in white matter, they contribute to structural integrity and repair.
