Gynecologic and REI Embryology and Developmental Biology

1
Gynecologic and REI Embryology and Developmental
Biology

• M M Pearce, MD
• University of Tennessee
• Department of Obstetrics and Gynecology
• 14 October 2004

2
Objectives

• Describe the embryology of normal mullerian tract
  development

• Describe the pathophysiology of mullerian
  agenesis and dysgenesis
• Describe the pathophysiology of disorders of
  sexual differentiation

3

• Linear explanations of each would require
  frequent repetition of each sequence
• Parallel explanations lend themselves to a
  discussion of normal and abnormal development
  together
• This will be organized as follows

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Overview of Organization

• Define types of sexual differentiation
• Outline normal and abnormal chromosomal
  differentiation
• Outline embrylogical processes that lead to
  normal and abnormal gonadal development
• Outline processes that lead to normal and
  abnormal phenotypical development

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• 500 years ago, Paracelsus stated that a Man
  should be begotten without the female body and
  the natural womb. I answer hereto, that it is
  perfectly possible

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Aureolus Philippus Theophrastus Bombast von
Hohenheim, known to most people simply as
Paracelsus. "De Natura Rerum" in 1572

• "Now, this is one of the greatest secrets which
  God has revealed to mortal and fallible man. It
  is a miracle and a marvel of God, an arcanum
  above all arcana, and deserves to be kept secret
  until the last of times, when there shall be
  nothing hidden, but all things shall be manifest.
  And although up to this time it has not been
  known to men, it was, nevertheless, known to the
  wood-sprites and nymphs and giants long ago,
  because they themselves were sprung from this
  source since from such homunculi when they come
  to manhood are produced giants, pygmies,and other
  marvelous people, who get great victories over
  their enemies, and know all secrets and hidden
  matters".

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Anton von Leeuwenhoek, early microscopist
Examined sperm and drew what he thought he saw
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Anton von Leeuwenhoeks perception of spermatozoa
1685
Meanwhile, 400 years later
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The Big Picture
SRY
NO SRY
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Sex Determination

• In humans it is generally regarded that there are
  two sexes, but they can actually be
  differentiated in several ways
• Chromosomal sex Males usually have one X and one
  Y chromosome in their body cells while females
  usually have two Xs.
• Gonadal sex Males usually have testes, seminal
  vesicles, prostate gland and associated tubing,
  while females usually have ovaries, uterus and
  oviducts.
• Phenotypical sex Males are typically larger than
  females and possess external genitalia.

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Sexual Differentiation

• Therefore, there are 3 levels of sexual
  dimorphism
• Chromosomal sex
• Gonadal sex
• Phenotypic sex
• Genetic sex determines gonadal sex determines
  phenotypic sex.

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First LevelChromosomal Sex

• XY (nml) or XXY or XXYY or XXXY or XXXXY Male
  (testis)
• XX (nml) or XXX Female (ovary)
• XO Female with incomplete ovarian development
• XXY or XXYY or XXXY or XXXXY testis but
  impaired sperm production

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Y makes you male

• Therefore
• The primary gene that controls testicular
  differentiation is on the Y chromosome in
  mammals.
• Individuals with a Y chromosome almost always
  have a "male" phenotype

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Fertilization

• Genetic (chromosomal) sex is determined at the
  moment the egg is fertilized by sperm
• Depends on the presence or absence of the Y
  chromosome

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The Y chromosome

• Humans with as many as four X chromosomes and a
  single Y chromosome develop into males

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The Y chromosome- SRY Gene

• Contains a gene called the SRY, (sex- determining
  region, Y chromosome)
• The SRY gene encodes a regulator that is proposed
  to trigger a cascade of events ending in testes
  formation
• SRY gene is both necessary and sufficient for
  male sex determination

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The Y chromosome

• Presumably arose from an ancestral homolog of the
  X chromosome
• Retains regions of homology at its ends
• Permit the Y to pair with X during meiosis
• SRY gene is located near these ends
• Allows the SRY to be transferred occasionally
  from the X to the Y
• Leads to a 46,XX male or 46,XY female

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How the Y chromosome interacts

• SRY Codes for a DNA binding protein and acts as
  a transcription factor or assists other
  transcription factors
• H-Y Antigen no longer believed to be involved
• The gene products are transcribed and regulate
  primary sex chord differentiation (formation of
  seminiferous tubules), androgen production and
  Antimullerian hormone (AMH)
• In the absence of the SRY protein, primary sex
  chord regress and secondary sex chords (egg
  nests) develop

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Disorders of chromosomal sex

• Turner Syndrome
• Klinefelter Syndrome
• Super Female
• Super Male

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Turner syndrome

• Typically have a 45,X karyotype, but all involve
  complete or partial absence of one sex chromosome
• Phenotypic females
• Only universal feature is short stature, but
  there are a range of abnormalities
• Common cause of amenorrhea
• Accounts for up to 10 of spontaneous abortions
• Affects one in 2500 female births

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Turner syndrome

• Short stature
• Sexual infantilism
• Webbed neck
• Broadly spaced nipples
• Gonadal dysgenesis

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Klinefelter syndrome

• Typically have a 47,XXY karyotype
• Predominantly male phenotype
• Patients exhibit small testes, smaller penis
  breast enlargement, and an absence of sperm in
  the ejaculate
• Low plasma testosterone and elevated circulating
  levels of estradiol
• Affects one in 500 newborn males

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Super Female

• Have a 47,XXX karyotype
• Female phenotype
• Typically will have diminished fertility
• Occasionally mental retardation

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Super Male

• Have a 47,XYY karyotype
• Normal male body type, with increased height
• Tend to have reduced sperm production and are
  often infertile
• Was termed super male because of a high
  coincidence of the karyotype with violent,
  aggressive criminals since largely discredited
• Affects one in 1100 male births

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Embryo immediately before differentiation

• Stage 17 or 42 to 44 days (8 weeks since LMP)
• Male and female identical

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Next LevelGonadal sex

• Initially, gonads are identical in both sexes,
  termed indifferent gonads
• Both gonads develop from the urogenital ridges
• Or, in other words

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In the beginning

• There is no difference in male and female
  development during the first six weeks after
  conception, both sexes possess a mesenephros
  (protokidney) on which a ridge of bipotent tissue
  called the germinal ridge forms
• Can develop into a testis or an ovary

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Testis-Determining Factor

• The sex you will become is then determined by the
  TDF (Testis-Determining Factor) a protein encoded
  by the SRY gene. If the SRY gene is expressed,
  then the germinal ridge will become a testis,if
  not expressed then an ovary forms
• Partial expression of this gene results in
  incomplete gonadal differentiation.

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Gonadal sex

• First to form are the wolffian ducts
• At 6 weeks of gestation the müllerian ducts form
  immediately lateral to the wolffian ducts
• Gonadal differentiation begins around 7-8 weeks
  of gestation
• How does this come about?

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Gonads and Germ Cells

• Each gonad arises from a gonadal ridge, a
  thickening of intermediate mesoderm and
  overlaying coelomic mesothelium that develops
  ventromedial to the mesonephric kidney. The
  parenchyma of each gonad consists of supporting
  cells and germ cells
• supporting cells are derived from invading
  coelomic mesothelial cells, augmented by cells
  from disintegrating mesonephric tubules the
  invading cells form cellular cords (gonadal
  cords) that radiate into gonadal ridge mesoderm
• primordial germ cells arise from yolk sac
  endoderm they migrate to the gut and then
  through dorsal mesentery to reach the gonadal
  ridge
• Germ cells proliferate and migrate into cellular
  cords to become surrounded by supporting cells
  (germ cells that fail to enter a cellular cord
  undergo degeneration).

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Female
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Ovary

• The cellular cords that contain germ cells
  undergo reorganization so that individual germ
  cells become isolated, each surrounded by a
  sphere of supporting cellsforming primordial
  follicles.
• Germ cell and follicle proliferation is completed
  before birth. Germ cells (oogonia) differentiate
  into primary oocytes that commence meiosis, but
  remain frozen in prophase of Meiosis I until
  ovulation in the reproductively capable female.

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Disorders of gonadal sex

• Pure Gonadal Dysgenesis
• Complete Gonadal Dysgenesis
• Vanishing Testis Syndrome

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Pure gonadal dysgenesis

• Have a normal 46,XX or 46,XY
• Normal height, no associated somatic defects
• Gonadal development is arrested before AMH and
  androgens are produced
• Bilateral streak gonads are associated with an
  immature female phenotype

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Pure gonadal dysgenesis

• 46,XX-little known, some have homozygous
  mutations in FSH receptor, results in hypoplastic
  ovaries that retain some primary follicles
• 46,XY-male homozygous with same mutation,
  impaired spermatogenesis without azospermia

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Complete gonadal dysgenesis

• Wilms Tumor Related 1 (WT1)
• First autosomal gene linked to 46,XY
• Wilms tumoran embryonic kidney tumor
• Two distinct syndromes
• Denys-Drashgonadal and urogenital abnormalities
  along with diffuse mesangial sclerosis
• Frasiergonadal dysgenesis, impaired
  virilization, and focal glomerular sclerosis, but
  do not develop Wilms tumor

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Complete gonadal dysgenesis

• 46,XY with abnormally formed gonads, were on the
  path to testis differentiationgonadal streaks
• No androgen produced
• Wolffian ducts regress
• Müllerian ducts develop due to lack of AMH
• Female external genitalia
• Feminizing puberty with estrogen therapy

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Complete gonadal dysgenesis

• Steroidogenic Factor 1 (SF-1)
• SF-1 is required for the development of the
  indifferent gonads
• Mice lacking SF-1 exhibit adrenal and gonadal
  agenesis-have female internal and external
  urogenital tracts
• Studies suggest that SF-1 in humans plays roles
  in embryonic development of the adrenal glands
  and gonads

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Complete gonadal dysgenesis

• 46,XY patients with campomelic dysplasiasyndrome
  that includes skeletal, renal, and cardiac
  abnormalities

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Complete gonadal dysgenesis

• DAX-1 Dosage-Sensitive Sex Reversal
• Duplication of the short arm of the X
• DAX-1 is mutated in boys with adrenal hypoplasia
  congenita (AHC)
• Exhibit adrenal insufficiency
• Have a compound hypothalamic/pituitary defect
• Will lead to sex reversal

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Vanishing testis syndrome

• 46,XY males with a wide array of phenotype
• Absent or rudimentary testes that had some
  endocrine function at some time during sexual
  differentiation
• Ranges from complete failure to incomplete
  virilization
• Normal males with anorchia

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Vanishing testis syndrome

• Most severely affected are 46,XY phenotypic
  females
• Lack testes, accessory male reproductive organs,
  and are sexually infantile
• No müllerian duct derivatives are presents
• Testicular failure occurred between the onset of
  AMH biosynthesis and testosterone secretion

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So far, we have discussed normal and abnormal
chromosomal and gonadal development. And now,
The last levelPhenotypic Sex

• By Week 9 (11 wga), gonadal differentiation is
  well underway
• Week 8 heralds the onset of phenotypical
  differentiation

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Mullerian Ducts become

• Two paired müllerian ducts ultimately develop
  into the structures of the female reproductive
  tract. The structures involved include the
  fallopian tubes, uterus, cervix, and the upper
  two-thirds of the vagina. The ovaries and lower
  one third of the vagina have separate embryologic
  origins not derived from the müllerian system.

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Female phenotypical development- Mullerian
Development

• Wolffian ducts largely degenerate
• Cephalic ends of the müllerian ducts form
  fallopian tubes
• Caudal portion then fuses to form the uterus
• 9 weeks- uterine cervix is recognizable
• 17 weeks- myometrium formation is complete

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Female phenotypical development

• Vaginal development begins at 9 wks
• Uterovaginal plate forms between the caudal buds
  of the müllerian ducts and the dorsal wall of the
  urogenital sinus
• These cells will degenerate thereby increasing
  distance between the uterus and urogenital sinus
• Upper 1/3 of the vagina derives from müllerian
  ducts
• Remainder derives from the urogenital sinus

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How do problems arise?

• Complete formation and differentiation of the
  müllerian ducts into the segments of the female
  reproductive tract depend on completion of 3
  phases of development as follows
• Organogenesis
• Fusion, laterally and vertically
• Resorption

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Organogenesis

• First, Organogenesis One or both müllerian ducts
  may not develop fully, resulting in abnormalities
  such as uterine agenesis or hypoplasia
  (bilateral) or unicornuate uterus (unilateral).

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Fusion

• Lateral Fusion The process during which the
  lower segments of the paired müllerian ducts fuse
  to form the uterus, cervix, and upper vagina.
  Failure of fusion results in anomalies such as
  bicornuate or didelphys uterus.
• Vertical fusion refers to fusion of the ascending
  sinovaginal bulb with the descending müllerian
  system (ie, fusion of the lower one third and
  upper two thirds of the vagina). Complete
  vertical fusion forms a normal patent vagina,
  while incomplete vertical fusion results in an
  imperforate hymen.

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Septal resorption

• After the lower müllerian ducts fuse, a central
  septum is present, which subsequently must be
  resorbed to form a single uterine cavity and
  cervix. Failure of resorption is the cause of
  septate uterus

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Table I. Classification of Müllerian duct
anomalies
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Frequency

• In the US Müllerian duct anomalies are estimated
  to occur in 0.1-0.5 of women. The true
  prevalence is unknown because the anomalies
  usually are discovered in patients presenting
  with infertility. Full-term pregnancies have
  occurred in patients with forms of bicornuate,
  septate, or didelphys uteri therefore, true
  prevalence may be slightly higher than currently
  estimated. Simon et al found that in the healthy
  fertile population, müllerian duct anomalies have
  a prevalence of 3.2

Check this excellent web site out for an in-depth
explanation of every variant, with
recommendations of imaging studies, great
graphics http//www.emedicine.com/radio/topic738.
htm
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Ligaments

• When the mesonephros degenerates, it leaves
  behind a urogenital fold that becomes genital
  duct ligaments.
• In females, the urogenital fold becomes
• suspensory ligament of the ovary , mesovarium,
  mesosalpinx, and the cranial part of the
  mesometrium. The caudal part of the mesometrium
  is formed by a tissue shelf that accompanies
  each paramesonephric duct when it shifts medially
  to fuse with its counterpart.
• A caudal extension of the urogenital fold becomes
  the proper ligament of the ovary and round
  ligament of the uterus in females.

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Female phenotypic development

• After 10 weeks gestation
• The genital tubercle begins to bend caudally
  forming the clitoris
• The side portions of the genital swellings
  enlarge to become labia majora
• The posterior portions fuse becoming posterior
  fourchette
• The urethral folds persist to form labia minora

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Breast development

• 5 wks-paired lines of epidermal thickening
  extend from forelimb to hindlimb
• 6-8 wks-mammary lines largely disappear
• Except for a small portion on each side that
  condenses and penetrates the mesenchyme

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Breast development

• The pair of mammary buds undergoes little change
  until the 5th month
• At this point secondary epithelial buds appear
  and nipples begin to form
• Breasts development is identical in males and
  females before the onset of puberty

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Disorders of phenotypic sex

• Are termed disorders in which the phenotypic sex
  is ambiguous or is completely in disagreement
  with chromosomal and gonadal sex
• Generally result from a failure of synthesis or
  action of hormones that mediate male sexual
  differentiation or the inappropriate synthesis of
  androgens.

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Disorders of phenotypic sex

• Female Pseudohermaphroditism
• Male Pseudohermaphroditism
• Disorders of Androgen Biosynthesis
• Defects in Androgen Action
• Syndrome of Persistent Müllerian Ducts

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Anti-Müllerian Hormone

• Is very important that AMH not be expressed in
  females (would lead to the regression of the
  müllerian ducts)
• Persistent Müllerian duct syndrome in males
• Genetic and phenotypic males have Fallopian tubes
  and a uterus along with Wolffian duct male
  structures
• May be a failure to produce functional AMH or an
  inability to respond to it

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Androgens

• Testosterone is the principle androgen, secreted
  by testes
• Dihydrotestosterone, (DHT), is the 5a-reduced
  metabolite mediates many of the differentiating,
  growth-promoting, and functional actions of
  androgens, converted in certain target tissues

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Female hormones

• In the ovary, androstenedione and testosterone
  serve as precursors for estrogen formation
• Estradiol is the major estrogen produced in the
  ovaries
• Ovarian hormones seem to have no effects on
  female sexual differentiation

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Female Developmental Control

• All aspects of female development, ovarian,
  internal and external genitalia are essentially
  autonomous processes
• They apparently require no hormonally active
  inductive substances
• Likely that evolution favored development of the
  female as the neutral sex

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Female pseudohermaphroditism

• Individuals have ovaries and müllerian
  derivatives, but exhibit virilization of external
  genitalia to some degree
• Must be exposed in utero to androgens
• Degree of virilization depends on the stage of
  differentiation when exposed

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Female pseudohermaphroditism

• Karotype 46,XX
• Genitalia of females can range from clitoral
  enlargement to complete labioscrotal fusion and a
  penile urethra
• Internal female features are unaltered
• Occasionally when virilization is severe and a
  penile urethra forms, errors in sex determination
  are made

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Disorders of testosterone synthesis

• Defects in the synthesis of testosterone can
  cause both adrenal insufficiency and male
  pseudohermaphroditism
• Impaired androgen production in connection with
  Leydig cell hypoplasia can also lead to a severe
  form where 46,XY subjects have external female
  genitalia
• AMH is produced in these subjects

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Male pseudohermaphroditism

• 46, XY male with defective virilization
• Can result from
• Defects in androgen synthesis
• Defects in androgen action
• Defects in müllerian duct regression

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Disorders of androgen action

• Most disorders of male phenotypic development
  result from impaired androgen action
• Testosterone synthesis and müllerian duct
  regression is normal
• Defects in either conversion of testosterone to
  DHT or in androgen receptors
• Male development is incomplete

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Disorders of androgen action

• CAIS, Complete Androgen Insensitivity
  Syndrome46,XY normal appearing female external
  genitalia, testes located in the abdomen
• PAIS, Partial AIS46,XY ambiguous external
  genitalia, Wolffian ducts develop minimally

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Persistent Müllerian ducts

• Normal 46,XY phenotypic male with persisting
  müllerian duct derivatives
• Very rare and is usually diagnosed during surgery
  when inguinal hernias are noted to contain
  müllerian derivatives
• Testes are usually cryptorchid
• Generally fully virilized
• Impaired spermatogenesis

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Anomalous Sexual Differentiation

• So, in normal sexual differentiation there
  are many stages to this complex process and at
  each stage errors can occur.

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Congenital Adrenal Hyperplasia (CAH)

• Individuals with CAH have an autosomal recessive
  disorder producing adrenal enzyme deficiency of
  21-hydroxylase, and are thus unable to produce
  sufficient quantities of cortisol to inhibit the
  release of adrenocorticotropic hormone (ACTH) and
  subsequent steroid synthesis.
• The result is increased prenatal androgen
  production. Affected females display masculinised
  genitals.

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Androgen-Insensitivity Syndrome (AIS)

• This syndrome is an X-linked recessive genetic
  disorder in which the cell nuclei are
  unresponsive to the binding or utilization of
  androgens resulting in the failure of the male
  fetus to masculinise. Despite having high levels
  of testosterone the genitalia resemble the female
  form, and at puberty secondary female sexual
  characteristics can also present due to the
  estradiol from testosterone aromatization. These
  males not only physically resemble females but
  also tend to be feminine in gender and behavior.
  It is common to perform gonadectomies at puberty
  and for them to receive hormone therapy, to be
  reared as female.

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Idiopathic Hypogonadotropic Hypogonadism (IHH)

• This syndrome is caused by the insufficient
  release of gonadotropin releasing hormone from
  the hypothalamus, and is sometimes referred to as
  Kallmans Syndrome when accompanied by the
  developmental absence of the olfactory bulbs
  causing anosmia. Males with this syndrome are
  genetically normal, but do not receive sufficient
  testosterone prenatally. Their external genitals
  remain relatively unaffected due to the influence
  of maternal androgens, but their testes are
  small, do not produce sperm and at puberty
  secondary male sex characteristics fail to
  appear.

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5a -Reductase Deficiency

• The individual lacks an enzyme that converts
  testosterone to another steroid
  dihydrotestosterone (DHT) which can exert an even
  stronger effect on the developing body than
  testosterone. The internal genitalia of males
  develop normally but the external genitalia
  resemble that of females. The infant is typically
  raised as a girl but then at the next
  testosterone peak at puberty the external
  genitals suddenly become obviously male

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Goals

• 10 Goals
• 1) Name the gene responsible for male development
  (see slide Y Chromosome- SRY gene)
• 2) Describe the origin of primordial germ cells
  (see Gonads and Germ Cells)
• 3) Describe the 3 phases of müllerian duct
  development (see How Do Problems Arise?)
• 4) Discuss embryological origins of a septate
  uterus (see Septal Resorption)
• 5) Discuss the origin of the round ligament of
  the uterus (see Ligaments)
• 6) Discuss timing of female phenotypical
  development (see Female Phenotypical Development)
• 7) Describe the genotype phenotype seen in CAIS
  (see the 2nd slide -Disorders of Androgen Action)
• 8) Describe the major non-mullerian components of
  the normal female system (see Mullerian Ducts
  become)
• 9) Describe the role of mullerian tissue on
  Fallopian tube formation (see Female phenotypical
  development- Mullerian Development)
• 10) Discuss control mechanism in ovarian
  development, internal and external genitalia
  formation (see Female Developmental Control)