The packet's known-genes field and inheritance-pattern field are both empty, so this packet does not supply a gene list or a mode of inheritance, and no molecular mechanism is provided. For this reason no gene is named here. The GeneReviews text in the packet refers to four subtypes and to genotype-phenotype correlations that differ by subtype, and states that for some subtypes no such correlations have been identified, but the specific genes involved are not carried in the packet's gene fields. Biochemically, the review describes glycosaminoglycan accumulation as the basis of this lysosomal storage disease.

According to GeneReviews, formal diagnostic criteria for MPS III have not been established. The review describes suspicion in individuals with language and motor delays at ages one to three years; language and motor delays, behavioral problems including hyperactivity and aggression, and sleep disturbance at ages three to ten years; and intellectual disability, developmental regression, seizures and gait disorders from age ten years. The review states that clinical findings alone are not diagnostic.

Supportive laboratory findings described include abnormal urinary glycosaminoglycan analysis, which is suggestive of an MPS disorder but cannot identify a specific enzyme deficiency and has reduced sensitivity, so normal results do not rule out an MPS disorder. Imaging findings described include mild dysostosis multiplex on skeletal survey, hip deformities, brain MRI abnormalities such as white matter alterations, ventriculomegaly and diffuse cerebral atrophy, spinal stenosis, and valvular anomalies on echocardiogram. The review states that diagnosis is established in a person with suggestive findings in whom biallelic pathogenic variants in one of four genes or deficiency of the respective lysosomal enzyme has been identified. Its differential diagnosis table covers conditions with overlapping features.

The packet lists no orphan drug or FDA-approved treatment records for this condition, which indicates only that none are supplied here. GeneReviews states that, despite ongoing research, no treatments are currently clinically available for the primary manifestations of MPS III. It adds that hematopoietic stem cell transplantation and umbilical cord blood transplantation are not currently considered effective treatment options because of a lack of evidence of neurologic benefit, and that developmental gains from therapy may be short-lived given the progressive nature of the disease.

The review describes management directed at individual manifestations. For seizures it lists anti-seizure medication as determined by a neurologist; for neurodevelopmental delay, supportive speech, physical and occupational therapies; for psychiatric and behavioral issues, treatment as determined by a psychiatrist along with a physically safe home environment; for musculoskeletal problems, orthopedic care, physical therapy or hydrotherapy, and vitamin D therapy in the context of low bone mineral density; for hearing loss, ear tube insertion or hearing aids; for cardiovascular anomalies and visual impairment, care by the relevant specialist; and for feeding difficulty with malnutrition, gastrostomy tube placement. Other circumstances the review describes as carrying risk include anesthesia at centers with limited experience with difficult airways and hip surgery, because of osteonecrosis and collapse of the femoral head.

According to GeneReviews, life span in MPS III is unpredictable but shortened, with death usually occurring in the second or third decade of life secondary to neurologic disease or respiratory tract infections. The review states that some individuals with more slowly progressive, later-onset or mild disease live into their 30s, 40s or even 50s with excellent medical care, which it describes as atypical, and that adults have survived into their 60s in very rare instances. Neurologic decline is described as universal, with variation in rate within and among subtypes.

The packet lists nine active clinical trial records for MPS III, seven of which have details supplied. NCT02716246 is a phase 2 gene transfer study, sponsored by Ultragenyx Pharmaceutical Inc, titled as a phase I/II/III trial of scAAV9.U1a.hSGSH; it is recruiting, with dates from 2016-04-25 to 2029-03-01. NCT06333041 is a phase 2 study of cannabidiol in Sanfilippo syndrome, sponsored by the Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical Center; it is recruiting, from 2026-04-01 to 2028-12-01. NCT06567769 is a phase 1 study of GC1130A in Sanfilippo syndrome type A, sponsored by GC Biopharma Corp; its status is active, not recruiting, from 2024-11-21 to 2027-06-01. NCT06181136 is a phase 1 study of DNL126 in pediatric participants with MPS IIIA, sponsored by Denali Therapeutics Inc.; it is active, not recruiting, from 2023-12-07 to 2028-08-01. NCT04201405 is a phase 1 study of gene therapy with modified autologous hematopoietic stem cells in MPS IIIA, sponsored by the University of Manchester; it is active, not recruiting, from 2020-01-07 to 2026-10-30. NCT05825131 is a natural history study in Sanfilippo syndrome type IIIC, sponsored by Phoenix Nest and recruiting. NCT03655223 is the Early Check expanded newborn screening study, sponsored by RTI International, active, not recruiting.

The packet's research digest classifies 109 publications, mostly basic science and preclinical work. GeneReviews describes intrathecal enzyme replacement as an approach under investigation, with a trial in progress reporting decreased heparan sulfate in cerebrospinal fluid in MPS IIIA. The packet lists the Cure Sanfilippo Foundation as a patient organization.