Genetics: What is the molecular basis of this genetically condition? Why is Sabr

Question

Genetics:

What is the molecular basis of this genetically condition?

Why is Sabrina's parental ancestry relevant to this condition?

What are he typical manifestation of Fragiles X syndrome in males and which molecules laboratory techniques are necessary to confirm Fragile X Syndrome?

CASE 4 Sabrina, 15 years old, was rece wish to be informed about t rs old, was recently diagnosed with Fragile X syndrome. Her parents ioformed about the implications of the diagnosis for Sabrina and other brina was born at term after an uncomplicated pregnancy. Her Sa ly members. developm ent was delayed; she walked at 16 months and spoke her first words at 3 of age. She now receives special education. Mr And Mrs Jennings has another years of age. She n 11-year-old daughter and a 9-y Mr Jennings diagnosis is not known. Mirs Jennings graduated from high school and Works in sales at a local department store. Her 68-year-old father was recently diagnosed with dementia and some unexplained neurological symptoms. ear-old son; both are healthy and attend regular schools. is an engineer. A brother of his father was intellectually disabled, but a

Explanation / Answer

Fragile X-syndrome is a genetic condition, inherited in an X-linked dominant pattern (mutated gene causing the syndrome is in the X chromosome; dominant because one copy of the altered gene is enough to cause the disorder). Males are more affected than females.

Molecular basis of Fragile x syndrome: It is caused by expansion and hypermethylation of CGG triplet repeats in the FMR 1 (Fragile X Mental Retardation 1) gene. This causes FMR1 repression leading to lack of expression of the FMR protein (FMRP plays a role in the development of synapses, which are critical for relaying nerve impulses).

An individual who has 55 to 200 CGG repeats (premutation) can be called a carrier. Individuals with more than 200 CGG repeats can be called a mutant and show the symptoms. Sabrina would have inherited fragile X-syndrome from her mother (Mrs Jennings) who would have been a carrier (premutation). The possibility is the permutation in Sabrina’s mother changed or expanded to full mutation as it was passed to her, thus being retarded. However, Mr Jennings would have been normal while his brother had fragile X-syndrome which was inherited from their carrier mother.

Males with fragile X-syndrome have moderate intellectual disability, delayed speech development, attention deficit, less focus, unstable mood, autistic behaviours (less social interaction). With age, these males show characteristic physical features such as long face, large ears, flat feet, enlarged testicles after puberty.

There is a specific genetic test which detects mutation in the FMR1 gene (leading to fragile X-syndrome) by polymerase chain reaction or more preferably southern blot. The test is done using blood samples.

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