Clinical Guidance

To date no correlation between severity of disease and type of GNPTG pathogenic variant has been reported; however, predicted loss-of-function variants, such as the recurrent variants , , and , are associated with a severe phenotype . See for more details.

Source: GeneReviews — "Mucolipidosis III Gamma"

Diagnostic Criteria

Formal diagnostic criteria for mucolipidosis III gamma have not been established.

Suggestive Findings

Mucolipidosis III gamma (ML III) should be suspected in individuals with the following clinical and radiographic findings .

Clinical findings

• Growth rate deceleration

• Joint stiffness of the fingers, shoulders, and hips

• Gradual mild coarsening of facial features

• Genu valgum

• Spinal deformities including scoliosis and hyperlordosis

• No organomegaly

Radiographic findings. In early childhood, skeletal radiographs reveal mild-to-moderate dysostosis multiplex:

Source: GeneReviews — "Mucolipidosis III Gamma"

Differential Diagnosis

Mucolipidosis II (ML II), ML III/, and ML III are all UDPGlcNAc 1-P-transferase deficiency disorders . Whereas the clinical phenotypes of ML III/ and ML III can be difficult to distinguish, the severe phenotype of ML II is easily differentiated. In general, the ML III phenotype is less severe than ML III/. See for inherited disorders to consider in the differential diagnosis of ML III. Table 2. Genes to Consider in the Differential Diagnosis of Mucolipidosis III Gamma (ML III)

Management Guidelines

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs in an individual diagnosed with mucolipidosis III gamma (ML III), the evaluations summarized (if not performed as part of the evaluation that led to the diagnosis) are recommended.

Table 3.

Recommended Evaluations Following Initial Diagnosis in Individuals with Mucolipidosis III

System/Concern | Evaluation | Comment

Constitutional

| Height, weight, head circumference | To assess growth rate

Skeletal

| Pain assessment | To assess pain scores involvement

Musculoskeletal

| Orthopedics/ physical medicine rehab/ PT OT eval | Incl assessment of:

• Lower limb pain (can be significant)

• Gross motor fine motor skills

• Hip, knee contractures

• Limited range of motion of shoulders

• Stiffness of finger joints Dupuytren-like palmar contractures (starting in late childhood)

• Carpal tunnel syndrome

• Odontoid dysplasia risk of atlanto-axial dislocation

• Mobility, ADL, need for adaptive devices

• Need for PT (to improve gross motor skills) /or OT (to improve fine motor skills)

Complete skeletal survey | To better assess skeletal involvement

Metabolic

bone disease | DXA study; biomarkers reflecting bone metabolism | Perform baseline DXA scan:

• Children age 5 yrs

• Adults at time of diagnosis

Development

| Developmental assessment | • Incl motor, adaptive, cognitive, speech-language eval

• Eval for early intervention/ special education

Cardiac

| Clinical exam, EKG, echocardiogram | To assess for mitral aortic valve involvement usually beginning in...

Source: GeneReviews — "Mucolipidosis III Gamma"

Clinical Guidance

Vigorous stretching exercises are not recommended because they are ineffective, painful, and may damage the surrounding joint capsule and adjacent tendons.

Source: GeneReviews — "Mucolipidosis III Gamma"

Therapies Under Investigation

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

Source: GeneReviews — "Mucolipidosis III Gamma"

Surveillance Guidelines

Table 4. Recommended Surveillance for Individuals with Mucolipidosis III

Source: GeneReviews — "Mucolipidosis III Gamma"