Brain-Derived Neurotrophic Factor and Obesity in the WAGR Syndrome

WAGR syndrome is a syndrome affecting children where they become extremely vulnerable to several complications and conditions. The syndrome is of genetic nature and is developed in the child before birth. WAGR syndrome derives its name from four of its key symptoms where W stands for Wilms tumor which is a kidney cancer found mostly in children; A stands for Aniridia which is mainly the absence of iris in one’s eyes which causes several other eye complications like blurring of the vision; G stands for Genitourinary diseases where if the affected child is male his penis is undescended and the urinary tract is abnormally placed whereas if the child is a female then the ovaries are found to be not well developed and other complications occur. R stands for mental retardation which refers to the developmental delays and intellectual disabilities that the affected child develops. WAGR syndrome is said to be caused primarily by mutations on the adjacent genes located on a region of chromosome 11 (11p13).

Brain-derived Neurotrophic Factor acts mainly as a neurotransmitter modulator. Its actions and functions are extremely essential in the learning and memory of a person. It actively takes part in neuronal plasticity which helps in the learning and the memory. Its function is also quite big in neuronal survival and growth. Found in large number in the central nervous system, gut, and other tissues, it is seen to play various other important function. the brain-derived neurotrophic factor is seen to bind to a high-affinity factor receptor TrkB (tyrosine kinase B). This action is responsible then for another crucial action that is the activation of signal transduction cascades (IRS1/2, PI3K, Akt). All of this is again found to be very important for the production of CREB and CBP who together encode proteins found in beta cell survival.

WAGR Syndrome happens due to heterozygous contiguous gene deletions. The two genes that are seen to be most affected are WTI and PAX6. These are the two adjacent genes located on chromosome 11p13 region. The position of these genes is said to be 4 MB centromeric to the brain-derived neurotrophic factor locus at 11p14. Various studies have been conducted to learn about the role it plays in humans. The mutations in WTI and PAX6 4 MB centromeric to the brain-derived neurotrophic factor are mainly the reason behind the occurrence of WAGR syndrome which further gives rise to Wilms tumor, aniridia, genitourinary diseases and mental retardation in the affected individuals.

One study reveals that hyperphagia and obesity were present as symptoms in a subgroup of WAGR syndrome. This study was conducted on the basis of a hypothesis. The hypothesis maintained that the subphenotype of obesity that is being located in individuals suffering from WAGR syndrome is actually the result of deletions that ultimately causes haploinsufficiency of brain-derived neurotrophic factor.

The method used to carry out this study was detailed research, examination, and study was done to understand the crucial relationship between genotype and body mass index. The International WAGR Syndrome Association referred a total of 33 patients suffering from WAGR Syndrome. Oligonucleotide comparative genomic hybridization was employed to accurately understand the true extent and actual potential of all the deletions^[1].

The range of deletions found in the involved patients was quite diverse. It started from 1.0 MB and extended to 26.5 MB. The body mass index was high in the patients in whom the heterozygous brain-derived neurotrophic factor deletions were found. The percentage of patients who had these deletions were 58. The body mass index was higher throughout their childhood in these patients. It was higher than those patients in whom the brain-derived neurotrophic factor was found to be intact and normal.

Obesity was found to have developed in 100 percent of patients with the heterozygous brain-derived neurotrophic factor by the age of 10. Though the serum brain-derived neurotrophic factor was less in these patients, the chances of obesity were high and the region that gave rise to this obesity was found within 80 kb of exon 1 of brain-derived neurotrophic factor.

The brain-derived neurotrophic factor is associated with obesity in many individuals suffering from WAGR syndrome, though not all.

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