To continue the MIR Project 2.0 and thanks to comments by Dr. Ismael Ejarque, medical geneticist, published in my blog the answers to the questions of Genetics of the MIR examination this year.
VERSION 1: Q 199: A woman (Consultant) 31 years of age and asymptomatic, presents gestation of 10 weeks according to ultrasound (primipara). His younger brother (index case) of 26 years is affected ataxia and genetically diagnosed as heterozygous carrier of a mutation expansive than 70 CAG repeats in the SCA3 gene (chromosome 14). The Consultant is derived from the genetic counseling clinic that values \u200b\u200bpossible chorion biopsy to study the fetal genotype. Is this invasive procedure as described pre-natal diagnosis (PND) in this case?
1. Is indicated after studying the genotype of the consultant and only if it is heterozygous.
2. There is no indication, as the ataxia SCA3 penetrance is complete and the consultant is asymptomatic and therefore did not inherit the mutation.
3. Can be indicated in the next pregnancy, after studying the genotype of the first child and to detect the mutation in it.
4. The ataxia SCA3 is recessive, so there is no appreciable risk of disease transmission and DPN is not indicated.
5. Is indicated whatever the genotype of the Consultant, as the ataxia SCA3 is maternally inherited (inherited from females).
The SCA3 is the spinocerebellar ataxia type 3 also called Machado-Joseph disease. It is caused by mutations in the gene ATXN3 by the mechanism of triplet repeat expansion of CAG. The affections are between 52 and 86 CAG repeats in heterozygosity with complete penetrance.
who has the mutation in heterozygosity with the disease since its herecia pattern is autosomal dominant. In this clinical case, with the disease and has the heterozygous mutated gene is the brother (aged 26) of pregnant women.
do think that before chorion biopsy should do the study to the pregnant woman to know what is their status in terms of gene ATXN3. She has a 50% percent chance of carrying the mutation and the disease, but being 31 years old I think he should have had symptoms. However, I do genetic testing to pregnant women to heal in health. If you leave without mutation, there would be more to do because they no longer transmit the disease. If you were carrying the mutation, then we would chorion biopsy.
Responses 1 and 2 are both true, but I think the answer 1 is more certain than the 2.
More information on this link: http://www.ncbi.nlm.nih.gov/books/NBK1196/
In this link you can see the nomenclature of the gene and the gene is said SCA3 is the same as saying ATXN3 gene: http://www.genenames.org/
2. There is no indication, as the ataxia SCA3 penetrance is complete and the consultant is asymptomatic and therefore did not inherit the mutation.
3. Can be indicated in the next pregnancy, after studying the genotype of the first child and to detect the mutation in it.
4. The ataxia SCA3 is recessive, so there is no appreciable risk of disease transmission and DPN is not indicated.
5. Is indicated whatever the genotype of the Consultant, as the ataxia SCA3 is maternally inherited (inherited from females).
The SCA3 is the spinocerebellar ataxia type 3 also called Machado-Joseph disease. It is caused by mutations in the gene ATXN3 by the mechanism of triplet repeat expansion of CAG. The affections are between 52 and 86 CAG repeats in heterozygosity with complete penetrance.
who has the mutation in heterozygosity with the disease since its herecia pattern is autosomal dominant. In this clinical case, with the disease and has the heterozygous mutated gene is the brother (aged 26) of pregnant women.
do think that before chorion biopsy should do the study to the pregnant woman to know what is their status in terms of gene ATXN3. She has a 50% percent chance of carrying the mutation and the disease, but being 31 years old I think he should have had symptoms. However, I do genetic testing to pregnant women to heal in health. If you leave without mutation, there would be more to do because they no longer transmit the disease. If you were carrying the mutation, then we would chorion biopsy.
Responses 1 and 2 are both true, but I think the answer 1 is more certain than the 2.
More information on this link: http://www.ncbi.nlm.nih.gov/books/NBK1196/
In this link you can see the nomenclature of the gene and the gene is said SCA3 is the same as saying ATXN3 gene: http://www.genenames.org/
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