What causes Triallelic patterns?
Triallelic patterns (7-9) can be due to length mutations that occur and segregate during an individual’s development, or to localized duplication of a locus, or to chromosomal trisomy.
What is the most common trisomy abnormality?
Down syndrome, on the other hand, is by far the most common chromosomal abnormality, affecting 1 in 800 babies. The risk of having a child with this condition increases with maternal age, rising exponentially after a woman reaches age 35.
Which trisomy is viable?
It is therefore interesting that trisomy 21 is the only viable autosomal trisomy, because the number of protein-coding sequences predicted for chromosome 21 is the smallest of any human chromosome, with the exception of the Y chromosome.
What does Triallelic mean?
In a disorder inherited in a triallelic mode an affected individual carries three mutant alleles between two genes. In either pattern of inheritance, unaffected individuals may carry no mutations, one mutation in either gene, or one mutation in each gene.
What is Triallelic inheritance?
Mutation analysis of these BBS genes in a cohort of patients has led to the description of the novel phenomenon of ‘triallelic inheritance’, wherein families were identified in which three mutations from genes at two different BBS loci segregate with expression of the disease.
What is the cause of mosaic trisomy 8?
Mosaic trisomy 8 is a rare genetic condition caused by an extra chromosome. Sometimes called trisomy 8 mosaicism, this condition develops well before birth. It’s a result of an abnormality in how cells divide and replicate from the earliest stages of pregnancy. It’s a spontaneously occurring condition.
How many chromosomes are involved in double trisomy?
However, some cases of double trisomies involving chromosomes 8, 13, 18, 21, X and Y have been observed in liveborns, suggesting that lethality of the abnormality depends on which chromosomes are involved in the aneuploidy.
Are there any cases of double trisomy in miscarriage?
As far as we know, only 178 complete double trisomy cases including this survey have been reported so far among miscarriages and liveborns. Moreover, only one study concerning the origin of the additional chromosomes in double trisomy SA has been published to date ( Li et al ., 2005 ).
Is the mean gestational age lower for double trisomy?
Mean gestational age has been described to be significantly lower for double trisomy cases than that reported for single trisomy ones ( Reddy, 1997 ).