Question

in terms of imprinting describe uniparental disomy and how it can result in a disorder. Please be thorough

Answer 1

Hi Answer:

Answer: To understand the uniparental disomy first we must understand and know the answer to few background question just like: what is imprinting or genomic imprinting? What’s the cause of genomic imprinting and how it related to the uniparental disomy? As we know that zygote formation took place after the fusion of male (sperm) and female (egg) germ cells and this process is known as fertilization. After fertilization, every cell inherited two copies of genes- one from maternal side and one from paternal side and in normal cases these both copies are active or on, but in some cases only one copy either from father or from mother is active. And which copy will be active that depends upon the parent of origin. It is seen some specific genes are active only when they are inherited from father and some are active only when they are inherited from mother side. This phenomenon of activation of one copy at a time is known as genomic imprinting. The genes which undergo these phenomena either from any parent is known as stamped genes. The stamped genes are nothing else it’s just methylated segment of DNA. The methylation ensures that which gene from both parents will undergo genomic imprinting. By the change i.e. addition and deletion of a methyl group, the activity of genes can be controlled. It is seen that in human a very few genes undergo genomic imprinting and the exact reason behind this question that why some genes undergo genomic imprinting and other not? Is still unclear. Till time researcher found only that the all imprinted genes tend to make a cluster at the similar regions of chromosomes. In human two major clusters of imprinting, genes have been identified out that one is found on the short arm (p) chromosome number 11 (at position 11p15) and second is on the long (q) arm of the chromosome 15 (at the position of region 15q11 to 15q13).

After understanding the genomic imprinting lets understand the uniparental disomy. It is abbreviated as UPD. As discussed above that we get two copies of chromosomes from our parents one from mother and one copy from father, but in case of UPD, only the person got one copy either from one parent. The second copy is missing. This happens randomly during the development of egg or sperm cells. In some cases, UPD didn’t show any effect on the affected individual because some time the missing copy undergo genomic imprinting and the genes of the present copy are fully functional so the person affected from UPD show normal growth and have no effect of UPD. But in some cases the genomic copy which is present (as in UPD person have only one copy chromosome) either from any parents undergo genomic imprinting then there is the loss of gene functions and this loss causes several problems just like delayed development, intellectual disability, or other health problems.

The disorder causes by UPD: There are several genomic UPD disabilities are known the most well-known are Prader-Willi syndrome and Angelman syndrome. These disabilities are caused by the UPD or error full genomic imprinting of the genes which are present on the long arm of chromosome number 15.

Prader-Willi syndrome (PWS): it result when the child got both copies of the long arm of chromosome 15 from his/her mother. The babies having PWS have poor muscle tone and weak health. After 2-4 year of life, the child is unable to control his feeding habit or appetite. The overeating results in the fast weight gain bulged belly, obesity and type 2 diabetes.

Angelman syndrome (AS): it result when the child got both copies of the long arm of chromosome 15 from his/her father. The people suffering from AS has unusual look, short in height, speech problem and mental instability