Family aggregation is an important source of evidence for psychiatric genetics.
Which of the following is true with regard to genetic relatedness?
C. First-degree relatives share 50% of their genes in common. This genetic relatedness reduces to 25% among second-degree relatives and 12.5% among third-degree relatives. The possible contribution of genetic factors for a disorder can be studied using the resemblance of disease risk across successive generations. A strong genetic contribution is suggested by a 50% decrement in disease risk with successive generations. If the risk decreases by more than 50% this suggests that the disease is either multifactorial with the possibility of significant gene– environment interaction or a more complex mode of genetic transmission. The ratio of the rate of the disorder in relatives to the population-based rate is commonly denoted by λ. This does not refer to linkage equilibrium. For diseases that are autosomal dominant in inheritance, λ tends to exceed 20; for complex multifactorial disorders, λ derived from family studies tends to range from 2 to 5.
Reference:
The proportion of phenotypic variation attributable to non-genetic causes among depressed patients is:
D. The proportion of phenotypic variation attributable to genetic causes is referred to as heritability in the broad sense. The proportion attributable to non-genetic causes includes shared and non-shared environmental variance, gene–environment covariance, and interaction. The estimate of heritability for major depression from twin studies is around 0.37. The relative risks based on the existing adoption studies suggest that the familial recurrence cannot be attributed solely to shared environmental factors. The remaining 63% of variance is almost wholly attributed to environmental factors unique to the individual.
Which of the following is true regarding the APOE gene in Alzheimer’s disease?
C. The apolipoprotein-E ε4 (APOE ε4) allele increases the risk of Alzheimer’s disease in a dose-dependent fashion. The odds of developing Alzheimer’s disease are 2.6−3.2 times greater in those with one copy, and nearly 15 times higher in those with two copies of the APOE ε4. A significant protective effect has been noted in those with ε2/ ε3 genotype. The population attributable risk due to APOE ε4 allele for Alzheimer’s dementia is very high due to its high frequency of occurrence in the general population. APOE ε4 can also increase the risk of vascular dementia.
References:
Which of the following genes implicated in schizophrenia potentially modulates D-amino acid oxidase?
C. A gene on locus 13q34, called G72, codes for D-amino acid oxidase activator (DAOA). A series of initial studies have identified this genetic locus as potentially contributing to schizophrenia susceptibility. The D-amino acid oxidase is the only enzyme oxidizing D-serine. D-serine is an important coagonist for the NMDA glutamate receptor. Hence it is posited that the variations in the G72 gene may influence the efficiency of glutamate gating at N-methyl-Daspartate-type (NMDA) receptors, but some later studies have failed to replicate the earlier findings. G72 has also been associated with depression in psychotic patients and also with bipolar disorder.
A transcriptome refers to:
B. Only a very small percentage (nearly 1.5%) of the human genetic code carried in DNA encodes proteins. This is because a large proportion of human DNA consists of long intron sequences, which are non-coding portions that get spliced out when transcription takes place. Hence, even when the complete sequence of a genome is known, mapping the functional genetic code will be difficult. A transcriptome is defined as all messenger RNA (mRNA) molecules transcribed from the DNA in a cell. The mRNA molecules act as ‘mediators’ between DNA codes and actual protein products. A transcriptome is not unique for a species or even for an individual; this is because what genes are transcribed in a cell depends on the kind of cell (e.g. WBCs, hepatocytes, epithelial cells) and what function is being carried out by the cell at that time. Hence, environmental influences or physiological needs will modify the transcriptome.
Click to expand