<prompt> Commonest genetic defect causing gonadal failure with primary amenorrheaKallman syndromeAbnormal X chromosome21-hydroxylase deficiencyTurner syndrome  <response>: Ans. d Turner syndrome Ref. Shaws Text book of Gynaecology 14th 97.Primary amenorrhea is defined as failure to menstruate by the age of 15in presence of normal secondary sexual development or withi 5 yrs after breast development, that occurs before age 10. The most common cause of primary amenorrhea is chromosomal abnormalities causing gonadal dysgenesis 45, such as Turners syndrome.Chromosomal syndromes1 Turners syndrome Commonest genetic defect causing gonadal failure with primary amenorrhea 45X0 Streak gonads Female genitalia with sexual infantilism Short stature Webbed neck Primary amenorrhoea Coarctation of the aorta and other variable physical features2 Klinefelters syndrome 47XXY Dysgenesis of the seminiferous tubules Male genitalia with small firm testicles Tall stature Gynecomastia Learningemotional difficulties3 True hermaphroditism 46XX or 46XY or mosaic, ovaries, testes or ovotestes Ambiguous or male genitalia with phallus Bifid scrotum and hypospadias4 Mixed gonadal dysgenesis Mosaic 45XO46XY, streak gonads with ambiguous or female genitalia with mixed internal organ Gonadectomy because of cancer risk and virilization5 Pure gonadal dysgenesis 46 XY or 46XX, streak gonads with female genitalia. 46XY is associated with clitoral hypertrophy, primary amenorrhoea, failure of sexual development and risk of gonadal cancer. 46XX - no clitoral hypertrophy and no gonadal cancer risk6 46XX males Undescended testes with maleambiguous genitalia Short stature Hypospadias. 