What Cytogenic Disorder Am I?

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euploid

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exact haploid number

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aneuploid

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error in meiosis or mitosis, not exact multiple of 23

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Usual causes for aneuploidy

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nondisjunction and anaphase lag

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result of nondisjunction occuring during gametogenesis

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gametes have 1 extra or 1 less chromosome than normal

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one chromosome in meiosis or mitosis lags behind and is left out of the cell nucleus

Results in one normal cell and one cell with monosomy

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anaphase lag

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result of monosomy of an autosome

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spontaneous abortion

A number of autosomal trisomies permit survival

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Mitotic errors in early development taht give rise to two or more populations of cells in same individual

May result from errors during the cleavage of fertilized ovum or in somatic cells

More common in autosomal chromosomes

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mosaicism

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Fanconi anemia, Bloom syndrome, and ataxia telangiectasia

Association with high level of chromosomal instability

Increased risk of cancers

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chromosome-breakage syndromes

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Loss of a portion of chromosome

Most are interstitial

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deletion

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break in chromosome arm

fragment with no centromere is produced

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terminal deletion

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break occurs at both ends of chromosome and they fuse together

Usually result in serious consequences

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ring chromosome

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Rearrangement that involves two breaks within a single chromosome with inverted reincorporation of the segment

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inversions

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inversions involving only one arm of chromosome

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paracentric

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Inversions involving breaks on opposite sides of the centromere

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pericentric

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One arm of a chromosome is lost and the remaining arm is duplcated

Once chromosome consisting of two short arms or two long arms

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isochromosome

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segment of one chromosome is transferred to another

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translocation

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Single breaks in each of two chromosomes with exchange of material

No loss of genetic material, individual is likely to be phenotypically normal

Increased risk for producing abnormal gametes

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balanced translocation

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translocation between two acrocentric chromosomes

Breaks close to centromeres of each chromosome

Transfer of segments leads to one very large chromosome and one very small chromosome

Compatable with normal phenotype but may cause abnormal progeny

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robertson translocation

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polysomal disease most often caused by nondisjunction

related to maternal age

Can derive from a robertson translocation, in which the carrier parent will have a 1 in 3 chances in bearing a child with the disorder

flat facial profile, epicanthic folds, oblique palpebral fissures, 80% have IQ between 25 and 50

High risk for congenital heart disease, leukemia, Alzheimers, intestinal stenosis,

Median death of 47 years

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Trisomy 21, Down's Syndrome

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Prominent occiput, metal retardation , micrognathia, short neck, overlappign fingers, congenital heart defects, renal malformations, limited hip abduction, rocker bottom feet

Most often results from meiotic nondisjunction

Death within a few months to a year

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Trisomy 18, Edward's Syndrome

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Micopthalmia, microcephaly and mental retardation, polydactyly, cleft lip and palate, cardiac defects, renal defects, umbilical hernia, rocker bottom feet

Most often results from meiotic nondisjunction

Death within a few months to a year

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Trisomy 13, Patau syndrome

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Variable features: congenital heart defects, abnormalities of the palate, facial dysmorphism, developmental delay, variable degrees of T-cell immunodeficiency and hypocalcemia.

Previously classified as DiGeorge syndrome or velcardiofacial syndrome

High risk for psychotic illness (schizophrenia, bipolar disorders)

Frequently have immunodeficiency

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22q11.2 deletion syndrome

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thymic hypoplasia, with resultant T-cell immunodeficiency, parathyroid hypoplasia giving rise to hypocalcemia, cardiac malformations affecting the outflow tract, mild facial anomalies

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DiGeorge Syndrome

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facial dysmorphism, cleft palate, cardiovascular anomalies, and learning disabilities

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velocardiofacial syndrome

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1. only one of the X chromosomes is genetically active
2. the other X of either maternal or paternal origin undergoes heteropyknosis and is rendered inactive
3. Inactivation maternal or paternal X occurs at random among al lthe cells of the blastocyst on the 16th day
4. Inactivation of the same X chromosome persists in all cells derived from each precursor cell

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Lyon Hypothesis

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Unique gene whose product is non coding RNA that is retained in the nucleus where it coats the inactive X chromosome and initiates a gene-silencing process by chromatin modification and DNA methylation

Turned off in the active X

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Xist

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Testes specific genes on Y chromosome involved in spermatogenesis

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MSY region

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Male hypogonadism that occurs when there are two or more X chromosomes and one or more Y

Increased length between the soles and pubic bone, eunuchoid body habitus with abnormally long legs; small atrophic testes often associated with a smll penis and lack of secondary sex characteristics; gynocomastia

Gonadotropin levels are consistantly elevated, testosterone levels are variably reduced, mean plasma estradiol levels are elevated

Principal cause of reduced sprmatogenesis and male infertility; sometimes tubles are totally atrophied and replaced by pink, hyaline, collagenous ghosts

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Klinefelter's Syndrome

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Leydig cells in Klinefelter Syndrome

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prominent , owing to atrophy and crowding of tubules

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Disorders associated with Klinefelter Syndrome

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breast cancer, extragonadal germ cell tumors, and autoimmune diseases

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polysomic X individuals in Klinefelter Syndrome

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have further physical abnormalities

Cryptorchidism, hypospadias, more severe hpoplasia of the testes, and skeletal changes such as prognathism and radioulnar synostosis

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Complete or partial monosomy of the X chromosome

Hypogonadism in phenotypic females

Edema of dorsum of the hand and foot, sometimes swelling of the nape of the neck in infancy

Bilateral neck webbing and persistent looseness of skin o nthe back of the neck, congenital heart disease (particularly preductal coarctation of the aorta and bicuspid aortic valve

Failure to develope secondary sex characteristics, infantile genetalia, inadequate breast development, little pubic hair, insulin resistance worsened by prescription of GH

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Turner syndrome

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structural abnormalities in X in Turner's syndrome mosaicism

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deletion of small arm resulting in isochrome of long arm

Deletion of portions of both long and short arm, resulting in the formation of a ring chromosome

Deletion of portions of the short or long arm

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Development of ovaries in Turner syndrome

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fetal ovaries develop normally early in embryogenesis

Absence of second X chromosome leads to accelerated loss of oocytes, which is complete by 2 years

Menopause before menarche

"streak ovaries"

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Short stature homeobox gene involved in Turner phenotype

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SHOX at Xp22.33

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sex determined by presence or absence of a Y chromosome

Y= boy regardless of how many X's might be present

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Genetic sex

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Sex based on histological characteristics of the gonads

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gonadal sex

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sex dependent on preence of derivatives of mullerian or wolffian ducts

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Ductal sex

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Presence of both ovarian and testicular tissue

sometimes teste on one side and ovary on the other

Sometimes combo= ovotestes

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true hermaphroditsm (very rare)

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disagreement between gonadal and phenotypic sex

Usually 46 XX karyotype

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pseudohermaphroditism

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genetic sex is XX, development of internal genitalia is normal

Only external genetalia virilized

due to excessive and inappropriate exposure to androgenic steroids during the early part of gestation -> usually due to fetal adrenal affected by congenital adrenal hyperplasia

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female pseudohermaphroditism

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Y chromosome present, gonads are exclusively testes

Genital ducts or external genitalia are incompletely differntiated along male phenotype

External genetalia is ambigous or phenotypically female

Defects in androgen synthesis, action, or both; most freqently caused by complete androgen insensitivity syndrome (mutations on receptor)

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male pseudohermaphroditism