30 Questions
What is the primary cause of chromosomal disorders?
All of the above
Which type of chromosomal imbalance is tolerated better?
Sex chromosomal imbalance
What is the characteristic of Trisomy 21 or Down Syndrome?
47 chromosome count
What is the result of partial deletion of the short arm of chromosome 5?
Cri du chat syndrome
Which of the following is a characteristic of autosomal disorders?
All of the above
What is the consequence of loss of chromosomal material?
More severe defects than gain of chromosomal material
What is the origin of the extra chromosome in Trisomy 21?
Maternal origin
What is the characteristic of Turner syndrome in infancy?
Swelling of the nape of the neck due to distended lymphatic channels
Which of the following disorders is associated with mutations in the SOX9 gene on chromosome 17q?
Camptomelic dysplasia
What is the typical karyotype of individuals with female pseudohermaphroditism?
46,XX
Which of the following diseases is caused by a triplet repeat mutation?
Myotonic dystrophy
What is the characteristic of Fragile X syndrome in males?
Macroorchidism
What is the typical inheritance pattern of Fragile X syndrome?
X-linked dominant
What is the result of expression of a FMR1 gene bearing a permutation in some males and females?
Fragile X tremor/ataxia
What is the characteristic cry of infants with Cri du Chat Syndrome?
A soft, mewing cry
What is the genetic defect associated with 22q11.2 Deletion Syndrome?
A small interstitial deletion of band 11 on the long arm of chromosome 22
What is the karyotype associated with Klinefelter Syndrome?
47,XXY
What is the characteristic facial feature of Trisomy 13 Patau syndrome?
Microcephaly
What is the primary immunological defect in 22q11.2 Deletion Syndrome?
T cell immunodeficiency
What is the characteristic body habitus of individuals with Klinefelter Syndrome?
Eunuchoid body habitus
What is the cardiac defect associated with 22q11.2 Deletion Syndrome?
All of the above
What is the estimated incidence of trisomy 21 among liveborn children or fetuses of mothers 35 years of age or older?
1/800
What is the characteristic facial feature of Down syndrome?
Flat nasal bridge
What is the percentage of patients with trisomy 21 who are mosaics, having a mixture of 46- and 47-chromosome cells?
1%
What is the most common type of chromosomal abnormality in Down syndrome?
Trisomy 21
What is the estimated recurrence risk in families when a parent, especially the mother, is a carrier of a Robertsonian translocation?
High
What is the characteristic feature of the hands in Down syndrome?
Single transverse palmar crease
What is the estimated incidence of Trisomy 18 (Edwards Syndrome)?
1/5,000
What is the characteristic heart defect in Trisomy 18 (Edwards Syndrome)?
All of the above
What is the characteristic intellectual disability in Trisomy 18 (Edwards Syndrome)?
Severe intellectual disability
Study Notes
Cytogenetic Abnormalities
- Chromosomal disorders associated with absence (deletion, monosomy), excess (trisomy), or abnormal rearrangements (translocations) of chromosomes
- Loss of chromosomal material produces more severe defects than does a gain
- Imbalances of sex chromosomes are tolerated much better than imbalances of autosomes
Autosomal Disorders
- Numerous rare chromosome disorders involving gain or loss of an entire chromosome or a chromosome segment
- Three well-defined non-mosaic chromosome disorders compatible with postnatal survival
- Trisomy 21 - Down Syndrome
- Trisomy 18 - Edwards Syndrome
- Trisomy 13 - Patau Syndrome
Trisomy 21 - Down Syndrome
- 95% of affected persons have trisomy 21, with a chromosome count of 47
- Meiotic nondisjunction, mostly in maternal meiosis I
- Characteristics:
- Growth retardation
- Mental retardation
- Multiple congenital anomalies
- Increased risk of developing acute leukemia and Alzheimer disease
- 1/800 born with Down syndrome among liveborn children or fetuses of mothers 35 years of age or older
Trisomy 18 - Edwards Syndrome
- 1/5,000 live births
- Characteristics:
- Small head
- Small jaw
- Clenched fists with overlapping fingers
- Severe intellectual disability
- Kidney malformations
- Structural heart defects at birth
- Intestines protruding outside the body (omphalocele)
- Esophageal atresia
- Prognosis: Poor, with many cases resulting in spontaneous abortion or death in early childhood
Trisomy 13 - Patau Syndrome
- Characteristics:
- Nervous system: Intellectual disability, motor disorder, microcephaly, holoprosencephaly, structural eye defects
- Musculoskeletal and cutaneous: Polydactyly, low-set ears, prominent heel, deformed feet (rocker-bottom feet)
- Urogenital: Abnormal genitalia, kidney defects
- Heart defects: Ventricular septal defect, patent ductus arteriosus, dextrocardia, single umbilical artery
Cri du Chat Syndrome
- Deletion of part of the short arm of chromosome 5
- Characteristics:
- Microcephaly
- Hypertelorism
- Epicanthal folds
- Low-set ears
- Micrognathia
- Crying infants with a mewing cat-like sound
- 1% of institutionalized mentally retarded patients
22q11.2 Deletion Syndrome - DiGeorge Syndrome
- Small interstitial deletion of band 11 on the long arm of chromosome 22
- Characteristics:
- Congenital heart disease
- Abnormalities of the palate
- Facial dysmorphism
- Developmental delay
- Thymic hypoplasia with impaired T cell immunity
- Parathyroid hypoplasia resulting in hypocalcemia
- T cell immunodeficiency and hypocalcemia are the dominant features
Sex Chromosomal Disorders
- Klinefelter Syndrome:
- 47,XXY karyotype
- Male hypogonadism
- Distinctive body habitus with an elongated body
- Reduced facial, body, and pubic hair
- Gynecomastia
- Mental retardation
- Increased risk of breast cancer and autoimmune diseases
- Turner Syndrome:
- 45,X karyotype
- Primary hypogonadism in phenotypic females
- Growth retardation
- Abnormally short stature
- Swelling of the nape of the neck
- Cardiovascular abnormalities
- Primary amenorrhea
- Clinical hypothyroidism
Disorders of Gonadal and Sexual Development
- Hermaphroditism: Both ovarian and testicular tissue present
- Gonadal Dysgenesis: Camptomelic dysplasia due to mutations in the SOX9 gene on chromosome 17q
- Denys-Drash syndrome: Chromosomally male patients with ambiguous external genitalia
- Frasier syndrome: Patients with XY complete gonadal dysgenesis
- Female Pseudohermaphroditism: 46,XX karyotype with normal ovarian tissue but ambiguous or male external genitalia
- Male Pseudohermaphroditism: 46,XY karyotype with incompletely masculinized or female external genitalia
Single-Gene Disorders with Atypical Patterns of Inheritance
- Fragile X Syndrome: Caused by a triplet repeat mutation, associated with autism-like symptoms, long face, and macroorchidism
- Huntington Disease: Associated with neurodegenerative changes
- Myotonic Dystrophy: Associated with neurodegenerative changes
This quiz covers clinical cytogenetics, specifically disorders of the autosomes and sex chromosomes, including gonadal and sexual development disorders. Based on Thompson & Thompson Genetics in Medicine, Chapter 6.
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