Long-term follow-up of 64 children with classical infantile-onset Pompe disease since 2004: A French real-life observational study

BACKGROUND

Classical infantile-onset Pompe disease (IOPD) is the most severe form of Pompe disease. Enzyme replacement therapy (ERT) has significantly increased survival but only a few studies have reported long-term outcomes.

METHODS

We retrospectively analyzed the outcomes of classical IOPD patients diagnosed in France between 2004 and 2020.

RESULTS

Sixty-four patients were identified. At diagnosis (median age 4 months) all patients had cardiomyopathy and most had severe hypotonia (57 of 62 patients, 92%). ERT was initiated in 50 (78%) patients and stopped later due to being ineffective in 10 (21%). Thirty-seven (58%) patients died during follow-up, including all untreated and discontinued ERT patients, and 13 additional patients. Mortality was higher during the first 3 years of life and after the age of 12 years. Persistence of cardiomyopathy during follow-up and/or the presence of heart failure were highly associated with an increased risk of death. In contrast, cross-reactive immunologic material (CRIM)-negative status (n = 16, 26%) was unrelated to increased mortality, presumably because immunomodulation protocols prevent the emergence of high antibody titers to ERT. Besides survival, decreased ERT efficacy appeared after the age of 6 years, with a progressive decline in motor and pulmonary functions for most survivors.

CONCLUSIONS

This study reports the long-term follow-up of one of the largest cohorts of classical IOPD patients and demonstrates high long-term mortality and morbidity rates with a secondary decline in muscular and respiratory functions. This decreased efficacy seems to be multifactorial, highlighting the importance of developing new therapeutic approaches targeting various aspects of pathogenesis.

Infant botulism: Two case reports and electroneuromyogram findings

Botulism is an uncommon severe neuromuscular disorder. We report two recent cases of confirmed infant botulism diagnosed in an 11-week and a 5-month-old infant along with electroneuromyogram (ENMG) findings. Then, we discuss the EMG features of infant botulism. In severe forms of infant botulism, presence of these features might help decide to use botulinum immune globulin. To our knowledge, case 1 is the first case reported in France based on confirmed dust contamination.

Thirteen new patients with guanidinoacetate methyltransferase deficiency and functional characterization of nineteen novel missense variants in the GAMT gene

Guanidinoacetate methyltransferase deficiency (GAMT-D) is an autosomal recessively inherited disorder of creatine biosynthesis. Creatine deficiency on cranial proton magnetic resonance spectroscopy, and elevated guanidinoacetate levels in body fluids are the biomarkers of GAMT-D. In 74 patients, 50 different mutations in the GAMT gene have been identified with missense variants being the most common. Clinical and biochemical features of the patients with missense variants were obtained from their physicians using a questionnaire. In 20 patients, 17 missense variants, 25% had a severe, 55% a moderate, and 20% a mild phenotype. The effect of these variants on GAMT enzyme activity was overexpressed using primary GAMT-D fibroblasts: 17 variants retained no significant activity and are therefore considered pathogenic. Two additional variants, c.22C>A (p.Pro8Thr) and c.79T>C (p.Tyr27His) (the latter detected in control cohorts) are in fact not pathogenic as these alleles restored GAMT enzyme activity, although both were predicted to be possibly damaging by in silico analysis. We report 13 new patients with GAMT-D, six novel mutations and functional analysis of 19 missense variants, all being included in our public LOVD database. Our functional assay is important for the confirmation of the pathogenicity of identified missense variants in the GAMT gene.

Mutations in SLC33A1 cause a lethal autosomal-recessive disorder with congenital cataracts, hearing loss, and low serum copper and ceruloplasmin

Low copper and ceruloplasmin in serum are the diagnostic hallmarks for Menkes disease, Wilson disease, and aceruloplasminemia. We report on five patients from four unrelated families with these biochemical findings who presented with a lethal autosomal-recessive syndrome of congenital cataracts, hearing loss, and severe developmental delay. Cerebral MRI showed pronounced cerebellar hypoplasia and hypomyelination. Homozygosity mapping was performed and displayed a region of commonality among three families at chromosome 3q25. Deep sequencing and conventional sequencing disclosed homozygous or compound heterozygous mutations for all affected subjects in SLC33A1 encoding a highly conserved acetylCoA transporter (AT-1) required for acetylation of multiple gangliosides and glycoproteins. The mutations were found to cause reduced or absent AT-1 expression and abnormal intracellular localization of the protein. We also showed that AT-1 knockdown in HepG2 cells leads to reduced ceruloplasmin secretion, indicating that the low copper in serum is due to reduced ceruloplasmin levels and is not a sign of copper deficiency. The severity of the phenotype implies an essential role of AT-1 in proper posttranslational modification of numerous proteins, without which normal lens and brain development is interrupted. Furthermore, AT-1 defects are a new and important differential diagnosis in patients with low copper and ceruloplasmin in serum.

[Infant coma in the emergency department: 2 cases of MCAD deficiency]

Medium-chain Acyl-CoA dehydrogenase deficiency (MCAD) is one of the most common fatty acid oxidation disorders. Clinical manifestations can be serious and lead to death if unrecognized. They are not specific and can mimic meningitis or an acute intestinal intussusception in its neurological form. Early recognition of MCAD and presymptomatic treatment of intercurrent illness improve the prognosis over the short- and long-term. MCAD deficiency satisfies the major criteria for newborn screening. We report the cases of 2 patients whose presentation was typical and severe. Early diagnosis of MCAD deficiency helped to start a simple treatment in both patients aimed at preventing further decompensation.

[A case of acquired encephalopathy in a child. A cause that we thought had disappeared]

Subacute central nervous system infection must be considered in any infant presenting with progressive encephalopathy. We present the case of an 18-month-old child with normal neuromotor development until the age of 14 months admitted for spastic hypertonia of the legs and arms associated with axial hypotonia. The mother reported that she recently had been found to be HIV-seropositive. HIV antibodies were negative during the first trimester of pregnancy. On the child's blood sample, the HIV test was positive associated with a major decrease in CD4 cell count. Viral load (ARN-PCR) was 720 copies par millilitre. On brain MRI, hypersignals were found in the white matter. HIV related encephalopathy caused by maternal fetal transmission was diagnosed. After 2 months of antiretroviral treatment (azidothymidine, lamivudine, and boosted lopinavir), the child's neurological condition improved. HIV infection must be suspected in all infants with progressive encephalopathy. The HIV test in pregnant women must be proposed at the beginning of pregnancy and repeated during the last trimester.