Pathology Cheat Sheet
Dosage, Storage, Morphology
Cytogenetics and storage disorders for NEET-PG: trisomy 21, Robertsonian translocation, Turner 45X, fragile X, Gaucher cells, and Tay-Sachs cherry-red spot.
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Dosage, Storage, Morphology
Cytogenetics and storage disorders for NEET-PG: trisomy 21, Robertsonian translocation, Turner 45X, fragile X, Gaucher cells, and Tay-Sachs cherry-red spot.
Common cytogenetic abnormalities of childhood and the lysosomal storage disorders, linking gene dosage and enzyme defects to morphology.
High-yield lines
- Nondisjunction is failure of chromosomes to separate, producing trisomic or monosomic zygotes.
- Trisomy 21 is the most common autosomal trisomy compatible with life, with free trisomy from maternal meiotic nondisjunction in about 95 percent.
- Translocation Down syndrome usually involves a Robertsonian translocation such as rob(14;21) and is not related to maternal age.
- The atrioventricular septal (endocardial cushion) defect is the most characteristic cardiac lesion of Down syndrome.
- Turner syndrome is 45,X monosomy, and over 98 percent of such conceptions abort spontaneously.
- Robertsonian translocations fuse the long arms of acrocentric chromosomes 13, 14, 15, 21, and 22.
- Fragile X syndrome results from CGG repeat expansion in the FMR1 gene and shows anticipation across generations.
- Lysosomal storage disorders accumulate undegraded substrate because a specific hydrolase is deficient.
- Gaucher disease is caused by glucocerebrosidase deficiency, with pathognomonic Gaucher cells showing a crumpled tissue paper cytoplasm.
- Tay-Sachs disease results from hexosaminidase A deficiency with GM2 ganglioside accumulation, a cherry-red macular spot, and no organomegaly.
- Niemann-Pick disease type A is caused by sphingomyelinase deficiency with foamy macrophages and a cherry-red spot.
- Pompe disease is lysosomal acid alpha-glucosidase deficiency causing glycogen accumulation and cardiomegaly.
Mapped competency codes
- PA11.1
- PA11.3
Continue into the full chapter
This summary maps to PA11-genetic-and-paediatric-diseases.
Frequently Asked Questions
What is the most common cytogenetic cause of Down syndrome?
Free trisomy 21 from maternal meiotic nondisjunction, which accounts for about 95 percent of cases and increases in frequency with maternal age.
What is the characteristic cell of Gaucher disease?
The Gaucher cell, an enlarged macrophage with an eccentric nucleus and a crumpled tissue paper cytoplasm from stored glucocerebroside.
How does Tay-Sachs disease differ from Niemann-Pick disease?
Both show a cherry-red macular spot, but Tay-Sachs has hexosaminidase A deficiency without organomegaly, while Niemann-Pick type A has sphingomyelinase deficiency with hepatosplenomegaly and foamy macrophages.
What causes fragile X syndrome?
Expansion of a CGG trinucleotide repeat in the FMR1 gene, which silences the gene and shows anticipation in successive generations.
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