Acid Ceramidase Deficiency: New Insights on SMA-PME Natural History, Biomarkers, and In Cell Enzyme Activity Assay

Background and Objectives

Spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME) due to acid ceramidase deficiency is a rare disorder, allelic with Farber disease, resulting from recessive ASAH1 variants. Patients present in early childhood with muscle weakness due to anterior horn degeneration and/or progressive drug-resistant myoclonic epilepsy. Death usually results from respiratory complications or status epilepticus during adolescence.

Methods

We identified 9 patients with SMA-PME from 5 different families followed in neurology, rehabilitation, and genetics departments of university hospitals in France and the United States. During disease progression, motor functional scores were assessed for seven of them and C26-ceramide quantification on dried blood spots (DBSs) was performed for 4 of them. An in cell assay, measuring the degradation rate of ceramides in living skin fibroblasts, was also performed in 2 patients. Finally, a literature review was conducted.

Results

Twelve years after the molecular characterization of SMA-PME, here we present the detailed history of 9 patients from 5 different families with 4 new ASAH1 variants. The prospective follow-up for 4 of them allows us to evaluate the relevance of functional scales and of C26-ceramide assay on DBS, as a biomarker. In addition, an in cell assay could provide a more reliable level of the residual ceramidase activity. Based on a comprehensive literature review, we provide a detailed description of the natural history of the 44 patients with SMA-PME diagnosed to date and show a genotype-phenotype correlation for the 2 main variants and the disease onset.

Discussion

This study presents the detailed natural history of SMA-PME. Given the rarity of this disease and the current lack of a reliable biomarker for patient follow-up, this work may serve as a retrospective control group for future therapeutic trials.

DISP1 deficiency: Monoallelic and biallelic variants cause a spectrum of midline craniofacial malformations

PURPOSE

DISP1 encodes a transmembrane protein that regulates the secretion of the morphogen, Sonic hedgehog, a deficiency of which is a major cause of holoprosencephaly (HPE). This disorder covers a spectrum of brain and midline craniofacial malformations. The objective of the present study was to better delineate the clinical phenotypes associated with division transporter dispatched-1 (DISP1) variants.

METHODS

This study was based on the identification of at least 1 pathogenic variant of the DISP1 gene in individuals for whom detailed clinical data were available.

RESULTS

A total of 23 DISP1 variants were identified in heterozygous, compound heterozygous or homozygous states in 25 individuals with midline craniofacial defects. Most cases were minor forms of HPE, with craniofacial features such as orofacial cleft, solitary median maxillary central incisor, and congenital nasal pyriform aperture stenosis. These individuals had either monoallelic loss-of-function variants or biallelic missense variants in DISP1. In individuals with severe HPE, the DISP1 variants were commonly found associated with a variant in another HPE-linked gene (ie, oligogenic inheritance).

CONCLUSION

The genetic findings we have acquired demonstrate a significant involvement of DISP1 variants in the phenotypic spectrum of midline defects. This underlines its importance as a crucial element in the efficient secretion of Sonic hedgehog. We also demonstrated that the very rare solitary median maxillary central incisor and congenital nasal pyriform aperture stenosis combination is part of the DISP1-related phenotype. The present study highlights the clinical risks to be flagged up during genetic counseling after the discovery of a pathogenic DISP1 variant.

A Reversible Etiology of Progressive Motor Decline in a Previously Healthy Child

We describe the clinical presentation and evaluation of a 10-year-old boy who presented to our medical center with years of progressive proximal muscle weakness, muscle atrophy, and weight loss. In addition to a myopathic phenotype, he was found to have tachycardia, tremor, and learning difficulties. Electromyography revealed chronic myopathic changes and laboratory screening was notable for undetectable thyroid stimulating hormone. Follow-up testing revealed elevated thyroid peroxidase antibodies and thyroid stimulating immunoglobulins. Ultrasound examination revealed an enlarged heterogeneous thyroid gland. Four weeks after treatment with atenolol and methimazole, his strength and cognition began to improve. This case highlights the importance of evaluating for potentially reversible toxic-metabolic etiologies in children presenting with any progressive neurologic symptoms.