Top 25 Chromosomal Abnormalities Every Cytogenetic Technologist Should Know

Published 2026-04-15

Roughly 45–50% of the ASCP CG exam tests chromosome analysis and imaging — and within that, recognizing clinically significant abnormalities by karyotype, FISH pattern, or clinical scenario is the #1 highest-yield skill. Memorize these 25 and you'll cover the vast majority of what's tested.

Benchmark your readiness: Take our free Initial Assessment →

Constitutional (Germline) Abnormalities

1. Trisomy 21 — Down Syndrome

  • Karyotype: 47,XX,+21 or 47,XY,+21 (95% nondisjunction); 4% Robertsonian 46,XX,der(14;21)(q10;q10),+21; 1% mosaic.
  • Features: Hypotonia, characteristic facies, congenital heart defects, intellectual disability.

2. Trisomy 18 — Edwards Syndrome

  • Karyotype: 47,XX,+18
  • Severe developmental delay; most die in infancy.

3. Trisomy 13 — Patau Syndrome

  • Karyotype: 47,XY,+13
  • Holoprosencephaly, polydactyly, cleft lip/palate.

4. Monosomy X — Turner Syndrome

  • Karyotype: 45,X (~50%); mosaics 45,X/46,XX; isochromosome 46,X,i(X)(q10).
  • Short stature, gonadal dysgenesis, webbed neck.

5. Klinefelter Syndrome

  • Karyotype: 47,XXY (most common); 48,XXXY, 49,XXXXY more severe.
  • Tall stature, hypogonadism, gynecomastia, learning differences.

6. Triple X

  • Karyotype: 47,XXX — often clinically subtle; tall stature, mild learning issues.

7. XYY Syndrome

  • Karyotype: 47,XYY — tall stature; usually normal phenotype.

8. Cri-du-Chat

  • Karyotype: 46,XX,del(5)(p15.2) — terminal 5p deletion. High-pitched cry, microcephaly.

9. Wolf-Hirschhorn

  • Karyotype: 46,XY,del(4)(p16.3) — "Greek warrior helmet" facies, severe intellectual disability.

10. DiGeorge / 22q11.2 Deletion

  • FISH: TUPLE1 probe shows deletion. Cardiac defects, hypocalcemia, T-cell deficiency.

11. Williams Syndrome

  • Karyotype: 46,XX,del(7)(q11.23) — ELN gene deletion. Supravalvular aortic stenosis, "cocktail party" personality.

12. Prader-Willi / Angelman

  • Karyotype: 46,XY,del(15)(q11.2q13) — same deletion, different parent of origin (paternal = PWS, maternal = AS). Imprinting disorder.

13. Fragile X

  • Molecular: FMR1 CGG repeat expansion (>200 repeats = full mutation). Most common inherited intellectual disability.

Hematologic Malignancy Translocations

14. t(9;22)(q34;q11.2) — Philadelphia Chromosome

  • Genes: BCR-ABL1 fusion
  • Disease: CML (95%), ALL (~25% adult), AML (rare)
  • Probe: Dual-fusion BCR/ABL1
  • Clinical: Targeted therapy with imatinib (Gleevec) revolutionized treatment.

15. t(15;17)(q24;q21) — PML-RARA

  • Disease: Acute Promyelocytic Leukemia (APL / AML M3)
  • Treatment: ATRA (all-trans retinoic acid) — medical emergency to confirm rapidly.

16. t(8;21)(q22;q22) — RUNX1-RUNX1T1

  • Disease: AML M2 — favorable prognosis.

17. inv(16)(p13.1q22) / t(16;16) — CBFB-MYH11

  • Disease: AML M4Eo — favorable prognosis.

18. t(8;14)(q24;q32) — MYC-IGH

  • Disease: Burkitt lymphoma; variants t(2;8) and t(8;22).

19. t(14;18)(q32;q21) — IGH-BCL2

  • Disease: Follicular lymphoma (~85% of cases).

20. t(11;14)(q13;q32) — CCND1-IGH

  • Disease: Mantle cell lymphoma.

21. 11q23 Rearrangements — KMT2A (MLL)

  • Probe: KMT2A break-apart (many partners).
  • Disease: AML/ALL, especially infant ALL and therapy-related AML; poor prognosis.

22. del(5q), −7/del(7q), +8

  • Disease: MDS and AML — recurrent unbalanced changes; del(5q) syndrome responds to lenalidomide.

23. CLL Panel Abnormalities

  • del(13q14) — most common, favorable
  • +12 — intermediate
  • del(11q22.3) ATM — unfavorable
  • del(17p13) TP53 — worst prognosis

Solid Tumor / Sarcoma Translocations

24. t(11;22)(q24;q12) — EWSR1-FLI1

  • Disease: Ewing sarcoma. Probe: EWSR1 break-apart.

25. t(X;18)(p11;q11) — SS18-SSX

  • Disease: Synovial sarcoma.

Quick Reference: Prognosis at a Glance (AML)

Cytogenetics Prognosis
t(8;21), inv(16)/t(16;16), t(15;17) Favorable
Normal karyotype, +8, others Intermediate
Complex (≥3 abnormalities), −5/del(5q), −7, KMT2A, inv(3) Adverse

For the official risk stratification, see the NCCN Guidelines for AML and WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues.

Authoritative References for Deeper Study

  • Mitelman Database of Chromosome Aberrations in Cancer — searchable database of every published cancer karyotype.
  • OMIM (Online Mendelian Inheritance in Man) — clinical descriptions of every constitutional syndrome.
  • ACMG Technical Standards — clinical lab guidance.

Study Strategy

Don't just memorize the list — for every abnormality above, train yourself to answer four questions:

  1. What's the karyotype/probe pattern?
  2. What disease does it cause?
  3. What's the prognosis?
  4. Is there a targeted therapy?

That's how the ASCP CG exam asks these questions in clinical-scenario format.

Test Yourself Now

Take the free 20-question Initial Assessment → — sample questions on Down syndrome, Philadelphia chromosome, FISH probe selection, and more.

Want flashcards covering all 25 abnormalities plus 250+ more? Explore CruxSci membership → for unlimited adaptive practice.

Related Reading

  • Complete ASCP CG Study Guide — 8–12 week roadmap to certification
  • Cytogenetic Technologist Salary 2026 — state-by-state pay guide
  • ASCP CG Retake Guide — recovery plan if you didn't pass first time

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