Clinical Guidance

In the United States about two thirds of newly diagnosed affected individuals have a unique genotype. Although no firm genotype-phenotype correlations exist for this disease, there are some pathogenic variants for which enough data has been generated to make some conclusions. For example, the pathogenic variant appears to be neuroprotective; individuals with at least one copy of p.Arg610del will not develop neurologic manifestations and will have NPD-B disease. Individuals homozygous for p.Arg610del will have less severe disease than those with one copy in combination with a more severe variant . In contrast to individuals with other pathogenic variants, individuals homozygous for the p.

Source: GeneReviews — "Acid Sphingomyelinase Deficiency"

Diagnostic Criteria

Acid sphingomyelinase deficiency (ASMD) cannot be diagnosed solely on clinical grounds.

Suggestive Findings

Scenario 1 – Abnormal Newborn Screening (NBS) Result

NBS for ASMD is primarily based on quantification of acid sphingomyelinase activity on dried blood spots. At the time of writing, ASMD is not included on the United States Recommended Uniform Screening Panel and is performed in a limited number of states within the US. Several pilot studies have also been performed in Europe. Acid sphingomyelinase activity values below the cutoff reported by the screening laboratory are considered positive and require follow-up biochemical and/or molecular genetic testing for confirmation.

Source: GeneReviews — "Acid Sphingomyelinase Deficiency"

Differential Diagnosis

Lysosomal storage diseases (LSD). The clinical features of acid sphingomyelinase deficiency (ASMD) may overlap with other lysosomal storage diseases such as Gaucher disease; however, biochemical and/or molecular genetic testing permits clear distinction between these disorders. Recent studies of individuals with hepatosplenomegaly whose testing for Gaucher disease was normal were subsequently found to have ASMD [Author, personal communication]. Pulmonary infiltration and the low serum concentration of high-density lipoprotein cholesterol are distinctive features that are present very early in individuals with ASMD but not in those with Gaucher disease. Hepatosplenomegaly. Other hereditary disorders associated with hepatosplenomegaly are summarized in . Table 2. Disorders with Hepatosplenomegaly in the Differential Diagnosis of Acid Sphingomyelinase Deficiency

Management Guidelines

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs in an individual diagnosed with acid sphingomyelinase deficiency (ASMD), 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 Acid Sphingomyelinase Deficiency

System/Concern | Evaluation | Comment

Growth/Nutrition

| • Growth assessment

• Gastroenterology/ nutrition/ feeding team eval

| In persons w/NPD-A:

• Incl eval of aspiration risk nutritional status.

• Consider eval for gastrostomy tube placement in those w/dysphagia /or aspiration risk.

In persons w/NPD-B:

• Assess nutritional status incl appropriate caloric, calcium, vitamin D intake.

Bone age in children age 18 yrs | • Skeletal age, often delayed, is useful for interpreting DXA scans.

• Knowledge about additional potential growth yrs can be reassuring to families concerned about child's stature.

Liver function

| Serum chemistries incl liver transaminases (ALT, AST), albumin, clotting factors | To evaluate for progression of hepatic dysfunction

Liver elastography or FibroScan® | To evaluate for hepatic fibrosis cirrhosis

Liver biopsy in persons w/evidence of deteriorating liver function may be indicated if noninvasive means to ascertain fibrosis are not available. |

Hepatosplenomegaly

| Radiologic exam w/measurement of liver spleen size |

Hematologic

| Compete blood count | To evaluate for thrombocytopenia, leukopenia, anemia

Source: GeneReviews — "Acid Sphingomyelinase Deficiency"

Clinical Guidance

Individuals who have splenomegaly should avoid contact sports.

Source: GeneReviews — "Acid Sphingomyelinase Deficiency"

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.

Source: GeneReviews — "Acid Sphingomyelinase Deficiency"

Surveillance Guidelines

Recommendations for clinical monitoring of individuals with ASMD have been published . These were published prior to the availability of ERT. However, such evaluations should still be considered, even for those on ERT, to assess for the individual's response to targeted and supportive care and the emergence of new manifestations. Table 6. Recommended Surveillance for Individuals with Acid Sphingomyelinase Deficiency

Source: GeneReviews — "Acid Sphingomyelinase Deficiency"