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推 morrobay:附議！這個資料夠力啦！ 08/05 00:29
※ 引述《Pardice (一直走下去)》之銘言：
: 54 下列對於5α-reductase deficiency的敘述，何者錯誤？
: (A)這些女性患者的基因型為XY型
: (B)這些女性患者的乳房發育相當於正常女性
: (C)這些女性患者可能會有睪丸存在
: (D)這些女性患者體內無法使testosterone轉換為dihydrotestosterone
: 網路上找到的資料
:
: 這類病人染色體是正常的男性(46,XY)，有分化良好的睪丸，正常的男性內生殖器，沒
: 有子宮及輸卵管的存在，但是外生殖器確是不明確的。通常出生時，陰莖很小，像陰蒂一
: 樣；睪丸的位置在腹股溝或所謂的陰囊中。由於第二性徵的發育主要是雄性激素的作用，
: 因此到了青春期會有明顯的男性化，但不會出現男性女乳( Gynecomastia )。
: 申覆理由: 根據定義，有Y就是男人。此類病人根本不是女人，
: 每個選項敘述都有錯，建議送分。
: 同意請"附議"
: 不知道有沒有強者可以神到Novak...
: 目前學校圖書館的Novak被借走，...苦無有力資料佐證
Nelson Textbook of Pediatrics, 18th ed.
Chapter 589 – Disorders of Sex Development (Intersex)
DEFECTS IN ANDROGEN ACTION
5α-REDUCTASE DEFICIENCY.
Decreased production of dihydrotestosterone (DHT) in utero results in severe
ambiguity of the external genitals of the affected male fetus. Biosynthesis
and peripheral action of testosterone are normal.
The phenotype most commonly associated with this condition results in boys
who have a small phallus, bifid scrotum, urogenital sinus with perineal
hypospadias, and a blind vaginal pouch ( Fig. 589-3). Testes are in the
inguinal canals or labioscrotal folds and are normal histologically. There
are no mu"llerian structures. Wolffian structures—the vas deferens,
epididymis, and seminal vesicles—are present. Most affected patients have
been identified as females. At puberty, virilization occurs; the phallus
enlarges, the testes descend and grow normally, and spermatogenesis occurs.
There is no gynecomastia. Beard growth is scanty, acne is absent, the
prostate is small, and recession of the temporal hairline fails to occur.
Virilization of the wolffian duct is caused by the action of testosterone
itself, although masculinization of the urogenital sinus and external
genitals depends on the action of DHT during the critical period of fetal
masculinization. Growth of facial hair and of the prostate also appears to be
DHT dependent.
Click to view full size figure
Figure 589-3 5α-Reductase deficiency. (From Wales JKH, Wit JM, Rogol AD:
Pediatric Endocrinology and Growth, 2nd edition. Philadelphia,
Elsevier/Saunders, 2003, p 165.)
The adult height reached is close to that of the father and other male
siblings. There is, however, significant phenotypic heterogeneity. This has
led to a classification of such patients into 5 types of steroid 5α
-reductase deficiency (SRD) ranging from complete female (type 5), to partial
female (type 4), ambiguous (type 3), predominantly male with micropenis (type
2), and completely male phenotype without apparent undervirilization (type 1).
Several different gene defects leading to SRD have been identified in the 5α
-reductase type 2 gene, located on the short arm of chromosome 2, in patients
from throughout the world. Familial clusters have been reported from the
Dominican Republic, Turkey, Papua New Guinea, Brazil, Mexico, and the Middle
East. There is no correlation between severity of the genetic defect and
phenotype.
The disorder is inherited as an autosomal recessive trait but is limited to
males; normal homozygous females with normal fertility indicate that in
females DHT has no role in sexual differentiation or in ovarian function
later in life. The clinical diagnosis should be made as early as possible in
infancy; it should be distinguished from androgen insensitivity syndrome. The
biochemical diagnosis is based on finding normal serum testosterone levels,
normal or low DHT levels with markedly increased basal and especially
hCG-stimulated testosterone : DHT ratios (>17), and high ratios of urinary
etiocholanolone to androsterone and 5α to 5α metabolites. Children with
androgen insensitivity have normal hepatic 5α reduction and, thus, a normal
ratio of tetrahydrocortisol to 5α-tetrahydrocortisol, as opposed to those
with SRD.
Most but, importantly, not all children reared as females in childhood have
changed to male around the time of puberty. It appears that exposures to
testosterone in utero, neonatally, and at puberty contribute to the formation
of male gender identity. Much more needs to be learned about the influences
of hormones such as androgens as well as the influences of cultural, social,
psychologic, genetic, and other biologic factors in gender identity and
behavior. Infants with this condition should be reared as boys whenever
practical. Treatment of male infants with DHT results in phallic enlargement.
這autosomal recessive疾病只限男性胎兒，所以不可能會有女性患者
題意錯誤，建議送分
雖然這科不是考小兒科，但性別分化的議題還是小兒科專長領域吧
附上小兒科Bible，應該還夠力
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※ 編輯: bathape 來自: 118.171.175.5 (08/04 11:12)