Q91.1 Trisomy 18, mosaicism (mitotic nondisjunction)

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis. Exempt from present-on-admission (POA) reporting.

Risk adjustment (HCC)

• RxHCC V08: HCC 148 — Mild or Unspecified Intellectual Disability/Developmental Disorder

MS-DRG index

Defines the logic of DRG(s) 884 in MDC 19.

Approximate ICD-9-CM (GEMs)

• 758.2 Edwards' syndrome (approximate)

Code annotations containing back-references to Q91.1

Back-references to Q91

• Code First: D84.81 Immunodeficiency due to conditions classified elsewhere ("chromosomal abnormalities (Q90-Q99)")
• Type 1 Excludes: E25 Adrenogenital disorders ("chromosomal abnormalities (Q90-Q99)")
• Type 1 Excludes: Q92 Other trisomies and partial trisomies of the autosomes, not elsewhere classified ("trisomies of chromosomes 13, 18, 21 (Q90-Q91)")
• Type 1 Excludes: Z15 Genetic susceptibility to disease ("chromosomal anomalies (Q90-Q99)")

Diagnosis Index entries for Q91.1

• Syndrome › trisomy › 18 › mitotic nondisjunction
• Syndrome › trisomy › 18 › mosaicism
• Trisomy (syndrome) › 18 (partial) › mitotic nondisjunction
• Trisomy (syndrome) › 18 (partial) › mosaicism

Nearby codes

• Q91 Trisomy 18 and Trisomy 13
• Q91.0 Trisomy 18, nonmosaicism (meiotic nondisjunction)
• Q91.1 Trisomy 18, mosaicism (mitotic nondisjunction) (this code)
• Q91.2 Trisomy 18, translocation
• Q91.3 Trisomy 18, unspecified
• Q91.4 Trisomy 13, nonmosaicism (meiotic nondisjunction)
• Q91.5 Trisomy 13, mosaicism (mitotic nondisjunction)
• Q91.6 Trisomy 13, translocation