Genetics Topic 6 Disorders

Angelman Syndrome

Symptoms: Delayed development, seizures, balance and speech issues, intellectual disabilities, happy and excited demeanor, laughter, smiling, hand-flapping, short attention span

Mode of Inheritance: Possible for the UBE3A gene to be passed on and cause this disorder. Typically caused by a deletion in a maternal chromosome 15 or by paternal uniparental disomy.

Cri-du-chat Syndrome

AKA: 5p-

Symptoms: Intellectual disability, microcephaly (small head), hypotonia, wide-set eyes, low-set ears, small jaw, heart defect, speech trouble, a cry that sounds like a cat's

Mode of Inheritance: 10% inherit affected chromosome from parent. Usually caused by chromosome 5 missing.

Edwards Syndrome

AKA: trisomy 18, (47, +18)

Symptoms: 80% are female. Causes body abnormalities, slow growth, heart and lung defects, abnormalities of other organs, a small and abnormally-shaped head, clenched fists, overlapping fingers. Most die their first month alive, 5-10% live past their first year.

Mode of Inheritance: Occurs randomly as nondisjunction. Can be inherited if a parent carries a chromosome with a balanced translocation (translocation but parent has no gain or loss of info, just has increased risk of passing on a disorder). Advanced maternal age.

Down Syndrome

AKA: trisomy 21 (47, +21)

Symptoms: Intellectual disability, flattened face shape, outside corners of eyes pointing upward, short neck, tongue that tends to stick outside of the mouth. 1/2 have a heart defect, some have digestive abnormalities. 15% have hypothyroidism. Increased risk of hearing and vision issues, Alzheimers, autism, and leukemia. Temper tantrums, short attention span, speech impediments, obsessive or compulsive behaviors are common.

Mode of Inheritance: Caused by cells having an extra chromosome 21. Advanced maternal age.

Klinefelter Syndrome

AKA: (47, XXY)

Symptoms: Affects only males. Symptoms are not obvious at first. Delayed development as an infant, Shyness, dyslexia, low attention span and energy as a child. Above average height. Poor sexual development. Most aren't significantly affected and live normal lives. Increased risk of type 2 diabetes, cardiovascular disease, weak bones, autoimmune disorders, male breast cancer.

Mode of Inheritance: 60% result from maternal nondisjunction. Caused by having an extra X chromosome due to a mistake during egg or sperm formation

Martin Bell Syndrome

AKA: Fragile X Syndrome

Symptoms: Learning disabilities, cognitive impairment. Males usually more affected than females. Most males and 1/3 of females have an intellectual disability. Anxiety, ADD, autism, seizures, short attention span. Long and narrow face, flat feet, flexible fingers.

Mode of Inheritance: X-linked dominant. Women with a mutated FMR1 gene have an increased risk of having an affected child.

Patau Syndrome

AKA: Trisomy 13, (47, +13)

Symptoms: Lethal condition; half of all affected die in the 1st month, mean survival time is six months. Phenotypes involve cleft lip and palate, eye defects, polydactyly, and feet with large protruding heels. There are malformations of the brain and nervous system, as well as heart defects.


Mode of Inheritance: Caused by nondisjunction, causing an extra chromosome 13. Paternal age is related.

Prader-Willi Syndrome

AKA: 15q-

Symptoms: Chronic overeating leading to obesity and type 2 diabetes. Intellectual disabilities, temper tantrums, stubbornness, compulsive behavior, delayed puberty.

Mode of Inheritance: Caused by a deletion of the parental chromosome 15 or by maternal uniparental disomy.

Turner Syndrome

AKA: 45, X

Symptoms: Affects only females. Short stature, loss of ovarian function, infertility. Narrowed aorta. 30% have a webbed neck, low hairline, swollen hands and feet, skeletal abnormalities, or kidney issues. 1/3-1/2 have a life-threatening heart defect. Most have normal intelligence. Developmental delays, nonverbal learning disabilities, and behavior issues are common.

Mode of Inheritance: Nondisjunction from father. Caused by monosomy X.

XYY Syndrome

AKA: 47, XYY

Symptoms: Affects only males. Taller than average. Higher risk of learning disabilities, motor tics, seizures, asthma, ADHD, anxiety, depression, and autism. Excessive belly fat, large teeth, flat feet, fifth fingers that curve inward, wide-set eyes, scoliosis. 4.5% out of 197 prisoners institutionalized for violent and dangerous behavior have this syndrome.

Mode of Inheritance: Caused by an extra Y chromosome by a random event.

Wolf-Hirschhorn Syndrome

Symptoms: "Greek warrior helmet" face appearance of a flat nose bridge and a high forehead. Slow growth and development, failure to thrive, and a short stature. Mild to severe intellectual disability. Socialization skills tend to be strong while verbal and language skills are weaker. Seizures, dry skin, scoliosis, missing teeth, and cleft lip/palate. Eye, heart, genitourinary tract, and brain abnormalities.

Mode of Inheritance: 85-90% are not inherited cases and result from a chromosomal deletion. A small % have it because of a chromosomal abnormality called a ring chromosome (chromosome fuses and forms a ring shape). A small % inherits chromosome 4 with the deleted segment.