Turner no of chromosomes -
Ans. is 'a' i.e., 45 Molecular pathogenesis of Turner's syndromeo Turner's syndrome results from complete or partial monosomy of the X chromosome and is characterized primarily by hypogonadism in phenotypic females,o The genotype in Turner's syndrome is AOo As already discussed absence of Y chromosome allows the development of female gonads ovary,o So these patients have female gonads.o What is the abnormality produced due to loss o f one X chromosome.o Both X chromosomes are active durine oosenesis and are essential for normal development of ovaries.o In Turners syndrome fetal ovaries develop normally early in embryogenesis, but the absence of second X chromosome leads to loss of oocytes from the ovary' and the ovaries are atrophied,o The ovaries are reduced to atrophic fibrous strands devoid of ova and follicles "Streak ovaries". (Gonadal dysgensis)o Short stature in Turner *s syndrome is also attributed to the loss ofhomeobox (SHOX) gene.o Homeobox gene is present on both the X chromosomes and is responsible for skeletal development.o Loss of this gene in Turner's syndrome results in short stature,o Congenital cardiac defects occur in Turner's syndrome.o Turner's syndrome results from complete or partial monosomy of the X chromosome and is characterized primarily by hypogonadism in phenotypic females.o It is the most common sex chromosome abnormality in females.Features of Turner syndrome in childreno The most severely affected patients generally present during infancy writh edema (owing to lymph stasis) of the dorsum of the hand and foot and sometimes swelling of the nape of the neck.o Swelling of the neck is related to markedly distended ly mphatic channels, producing so called cystic hygroma.o As these infants develop, the swelling subsides but often leave bilateral neck webbing and persistent looseness of skin on the back of the neck.o Congenital heart disease is also common, particularly preductal coarctation of Aorta and bicuspid Aortic valve,o C.V.S abnormalities are most important cause of mortality in children with Turner s syndrome.Features of Turner's syndrome in Adolescents and Adulto At puberty there is failure to develop normal secondary sex characteristics.o The genitalia remains infantile, breast development is inadequate and there is little pubic hair. Nipples are widely- spaced.o Turner syndrome is the single most important cause of primary- amenarrhoea accounting for approximately 1/3 of the cases.a Short stature (height rarely exceeds 150 cm).o The mental status of these patients is usually normal but subtle defects in nonverbal, visual spatial information processing have been noted (Recall that mental retardation is associated with the presence of extra chromosome) not with loss of X chromosome.o About 50% of the patients develop autoantibodies directed to the thyroid gland and upto one half of these patients develop hypothyroidism.o Glucose intolerance, obesity and insulin resistance are also seen.
45
47
46
42
Mendelian Disorders: Single-Gene Defects