Can a Genetic Counselor Use a Karyotype to Identigy a Carrier of Cystic Fibrosis?
Sunday, October 3rd, 2010 at
9:28 am
stgb93 asked:
Explain.
Tagged with: Carrier • Cystic Fibrosis • Genetic Counselor
Filed under: Cystic Fibrosis
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No.
CF is an autosomal recessive disease. 2 mutant alleles are required to manifest disease. Carriers will have 1 mutant allele.
The most common (70%) mutations is a 3 base deletion in the CFTR gene. This means the mutant gene is 3 bases shorter than the normal. The deletion results in a gene product that is devoid of the amino acid phenylalanine at position 508.
i.e. an abnormal deletion and so a shorter gene.
This can be detected using the following techniques:
1- PCR followed by gel electrophoresis:
This will identify 3 bases shorter gene.
2- ASO probes and Dot blot.
This will identify the abnormal gene presence of absence.
These methods are used to identify disease as well as carriers.
Since the majority of mutations in CF is a 3 base deletion karyotype analysis will not help.
Karyotype is most useful for chromosomal analysis where the number of chromosomes are in question.
eg. Downs syndrome pt. have three 21 chromosomes and Klinefelter syndrome pt. have two X chromosomes.
Ctstic fibrosis is a gene mutation carried on chromosome number 7 and would NOT show up on a karyotype.