Mendelian Disorders

Question 1

MC of chromosomal disorders

LEADING CAUSE of Mental retardation

Answer 1

TRISOMY 21

Causes:
Nondisjunction (95%)
Robertsonian translocation (4%)
Mosaicism (1%)

Question 2

Associations with Trisomy 21

Answer 2

endocardial cushion defects
Hirschsprung disease, duodenal atresia
ALL or AML (MC)
early onset Alzheimer’s disease

Question 3

Features of Trisomy 21

Answer 3

flat facial profile
oblique palpebral fissure
epicanthic folds

Question 4

Common features: mental retardation, cardiac and renal defects, rocker-bottom feet

Answer 4

Trisomy 18 (Edward syndrome) and Trisomy 13 (Patau syndrome)

Question 5

mental retardation, cardiac and renal defects, rocker bottom feet

cleft lip and palate and umbilical hernias

Answer 5

Trisomy 13 (Patau syndrome

Question 6

One of the most common genetic diseases involving sex chromosomes and male hypogonadism

Answer 6

KLINEFELTER SYNDROME (XXY)

HYPOGONADISM
MVP
gynecomastia
low IQ

Question 7

Complete or partial monosomy of X chromosome

Single most important cause of primary amenorrhea

Answer 7

TURNER SYNDROME (XO)

OVARIAN STREAKS
(-) secondary characteristics and short stature
cystic hygromas of neck –> regress –> WEBBED NECK
preductal CoA, bicuspid aortic valve

Question 7

Complete or partial monosomy of X chromosome

Single most important cause of primary amenorrhea

Answer 7

TURNER SYNDROME (XO)

OVARIAN STREAKS
(-) secondary characteristics and short stature
cystic hygromas of neck –> regress –> WEBBED NECK
preductal CoA, bicuspid aortic valve

Question 8

The MOST IMPORTANT cause of increased mortality in children w/ Turner Syndrome

Answer 8

preductal CoA, bicuspid aortic valve

Question 9

2nd MCC of mental retardation after Trisomy 21

Answer 9

FRAGILE X SYNDROME

CGG expansion in FMR1 gene in x chromosome

MACRO ORCHIDISM

Question 9

2nd MCC of mental retardation after Trisomy 21

Answer 9

FRAGILE X SYNDROME

CGG expansion in FMR1 gene in x chromosome

MACRO ORCHIDISM

Question 10

Defect in a-subunit of HEXOSAMINIDASE A

GM2 ganglioside - neurons and retina

Answer 10

TAY-SACHS DISEASE

(+) cherry red spot macula
(-) hepatosplenomegaly

Question 11

Defect in SPHINGOMYELINASE

sphingomyelin

Answer 11

NIEMANN-PICK DISEASE (A and B)

(+) cherry red spot macula
(+) hepatosplenomegaly
ZEBRA BODIE

Question 12

MC lysosomal storage disorder

Defect in GLUCOCEREBROSIDASE deficiency (B-glucosidase)

Answer 12

GAUCHER DISEASE

20 fold higher risk of developing Parkinson’s disease

Question 13

CAG expansion on HTT gene on CH4

Answer 13

HUNTINGTON DISEASE

progressive movement disorder
dementia

HUNTERS CAGe

Caudate - decreased Ach and GABA

Question 14

GAA

stepping gait
hypertrophic cardiomyopathy - MCC of death

Answer 14

FRIEDREICH ATAXIA

Question 15

Deletion in PATERNALLY derived chromosome 15

Answer 15

PRADER WILLI SYNDROME

mental retardation
profound hyperphagia
obesity
hypogonadism

Question 16

Deletion in MATERNALLY derived chromosome 15

Answer 16

ANGELMAN SYNDROME

mental retardation
ataxic gait
seizure
inappropriate laughter

Question 17

Deletion in MATERNALLY derived chromosome 15