2026 ICD-10-CM Diagnosis Code Q99.818

Clinical Information

• Clarin-1|CLRN1|Clarin 1|Usher Syndrome Type-3 Protein

  clarin-1 (232 aa, ~26 kda) is encoded by the human clrn1 gene. this protein is involved in the organization of the cytoskeleton in photoreceptor and auditory receptor cells.

• CLRN1 wt Allele|Clarin 1 wt Allele|RP61|USH3|USH3A|Usher Syndrome 3A Gene

  human clrn1 wild-type allele is located in the vicinity of 3q25.1 and is approximately 47 kb in length. this allele, which encodes clarin-1 protein, plays a role in sight and hearing. mutations in the gene are associated with usher syndrome 3a and retinitis pigmentosa 61.

• HARS1 wt Allele|CMT2W|HARS|HRS|Histidine Translase Gene|Histidine tRNA Ligase 1, Cytoplasmic Gene|Histidyl-tRNA Synthetase 1 wt Allele|Histidyl-tRNA Synthetase Gene|Jo-1 Antigen Gene|USH3B|Usher Syndrome 3B Gene

  human hars1 wild-type allele is located in the vicinity of 5q31.3 and is approximately 19 kb in length. this allele, which encodes histidine-trna ligase, cytoplasmic protein, is involved in trna aminoacylation. mutation of the gene is associated with axonal charcot-marie-tooth disease type 2w and usher syndrome type 3b.

• MYO7A wt Allele|DFNA11|DFNB2|MYOVIIA|MYU7A|Myosin VIIA (Usher Syndrome 1B (Autosomal Recessive, Severe)) Gene|Myosin VIIA wt Allele|Myosin, Unconventional Family VII, Member A Gene|NSRD2|USH1B

  human myo7a wild-type allele is located in the vicinity of 11q13.5 and is approximately 87 kb in length. this allele, which encodes unconventional myosin-viia protein, plays a role in intracellular transport affecting sight and hearing. mutations in the gene are associated with autosomal dominant deafness 11, autosomal recessive deafness 2 and usher syndrome type 1b.

• USH1G Gene|USH1G|USH1G|Usher Syndrome 1G (Autosomal Recessive) Gene

  this gene plays a role in both sight and hearing.

• USH1G wt Allele|ANKS4A|FLJ33924|SANS|Sans|Usher Syndrome 1G (Autosomal Recessive) wt Allele

  human ush1g wild-type allele is located in the vicinity of 17q25.1 and is approximately 7 kb in length. this allele, which encodes usher syndrome type-1g protein, is involved in the development of both the retina and cochlear hair cells. mutation of the gene is associated with usher syndrome 1g.

• USH2A wt Allele|RP39|US2|USH2|Usher Syndrome 2A (Autosomal Recessive, Mild) Gene|Usherin wt Allele|dJ1111A8.1

  human ush2a wild-type allele is located in the vicinity of 1q41 and is approximately 801 kb in length. this allele, which encodes usherin protein, plays a role in hearing and sight. mutations in the gene are associated with retinitis pigmentosa 39 and usher syndrome type 2a.

• Usher Syndrome

  a rare, autosomal recessive inherited syndrome caused by mutations in the cdh23, clrn1, gpr98, myo7a, pcdh15, ush1c, ush1g, and ush2a genes. it is characterized by hearing loss or deafness and progressive loss of vision. the loss of vision is the result of retinitis pigmentosa.

• Usher Syndrome Type 1

  a syndrome characterized by congenital, bilateral, severe sensorineural hearing loss, abnormalities in the vestibular system, and adolescent-onset retinitis pigmentosa.

• Usher Syndrome Type 2

  a syndrome characterized by congenital, bilateral sensorineural hearing loss that is mild to moderate in the low frequencies and severe to profound in the higher frequencies, no abnormalities in the vestibular system, and retinitis pigmentosa.

• Usher Syndrome Type 2C|USH2C

  an autosomal recessive sub-type of usher syndrome caused by homozygous or compound heterozygous mutation(s) in the adgrv1 gene, encoding adhesion g protein-coupled receptor v1. it may also result from biallelic digenic mutation(s) in adgrv1 and pdzd7, which encodes pdz domain-containing protein 7.

• Usher Syndrome Type 3

  a syndrome characterized by postlingual progressive hearing loss, abnormalities in the vestibular system, and onset of retinitis pigmentosa symptoms usually by the second decade of life.

• Usher Syndrome Type-1G Protein|Scaffold Protein Containing Ankyrin Repeats and SAM Domain|USH1G

  usher syndrome type-1g protein (461 aa, ~51 kda) is encoded by the human ush1g gene. this protein plays a role in retinal and cochlear development.

• Usherin|USH2A|Usher Syndrome Type IIa Protein|Usher Syndrome Type-2A Protein

  usherin (5202 aa, ~576 kda) is encoded by the human ush2a gene. this protein is involved in the functionality of cochlear hair cells and retinal photoreceptor cells.

New 2026 ICD-10-CM Code

Q99.818 is new to ICD-10-CM code set for the FY 2026, effective October 1, 2025. The National Center for Health Statistics (NCHS) has published an update to the ICD-10-CM diagnosis codes which became effective October 1, 2025. This is a new and revised code for the FY 2026 (October 1, 2025 - September 30, 2026).

MS-DRG Mapping for ICD-10-CM Code Q99.818

Diagnosis-Related Groups (DRGs) are used to classify hospital cases for billing and healthcare management. They help standardize how hospitals and other providers are reimbursed for inpatient care. Patients are grouped based on their principal diagnosis into broader categories called Major Diagnostic Categories (MDCs).

Once assigned to a DRG, the hospital receives a set payment for the patient’s care, regardless of the actual services provided. This fixed rate is intended to cover the typical cost of treating patients within that group. The payment amount depends on the DRG's relative weight, which reflects the expected complexity and cost of care based on the severity of the patient’s condition.

Diagnostic related groups encourage healthcare providers to focus on quality and efficiency in patient care while managing costs effectively. The diagnosis code is present in the following groups for version MS-DRG V43.0 applicable from 10/01/2025 through 09/30/2026.

Present on Admission (POA)

Q99.818 is exempt from POA reporting - The Present on Admission (POA) indicator is used for diagnosis codes included in claims involving inpatient admissions to general acute care hospitals. POA indicators must be reported to CMS on each claim to facilitate the grouping of diagnoses codes into the proper Diagnostic Related Groups (DRG). CMS publishes a listing of specific diagnosis codes that are exempt from the POA reporting requirement. Review other POA exempt codes here.

CMS POA Indicator Options and Definitions

Replacement Code

Q99818 replaces the following previously assigned ICD-10-CM code(s):

• Q99.8 - Other specified chromosome abnormalities

Code History

• FY 2026 - Code Added, effective from 10/1/2025 through 9/30/2026