Pelizaeus-Merzbacher Disease as a Rare Cause of Stridor in an Infant with Severe Reflux and Hypotonia

Stridor is high-pitched, noisy breathing that occurs as a result of a narrowed airflow. It is considered as a respiratory emergency in which if left untreated, may lead to death. The most common cause of stridor in paediatric is laryngomalacia (LM). Nevertheless, other causes of persistent stridor in infant have to be ruled out, in the case of failed surgical therapy. Here, we report a rare case of a three-month-old infant boy with persistent stridor since birth who had undergone aryepiglottoplasty for LM at day ten of life and was referred back to the hospital due to worsening of stridor with signs of respiratory distress and subsequently he was diagnosed with Pelizaeus-Merzbacher Disease (PMD). This is the first report to discuss on PMD as a rare differential diagnosis of stridor.

The Leukodystrophy Spectrum in Saudi Arabia: Epidemiological, Clinical, Radiological, and Genetic Data

Background: Leukodystrophies (LDs) are inherited heterogeneous conditions that affect the central nervous system with or without peripheral nerve involvement. They are individually rare, but collectively, they are common. Thirty disorders were included by the Global Leukodystrophy Initiative Consortium (GLIA) as LDs.Methods: We conducted a retrospective chart review of a consecutive series of patients diagnosed with different types of LD from four large tertiary referral centers in Riyadh, Saudi Arabia. Only those 30 disorders defined by GLIA as LDs were included.Results: In total, 83 children from 61 families were identified and recruited for this study. The male-to-female ratio was 1.5:1, and a consanguinity rate of 58.5% was observed. An estimated prevalence of 1:48,780 or 2.05/100,000 was observed based on the clinical cohort, whereas a minimum of 1:32,857 or 3.04/100,000 was observed based on the local genetic database. The central region of the country exhibited the highest prevalence of LDs (48.5%). The most common LD was metachromatic leukodystrophy (MLD), and it accounted for 25.3%. The most common disorder based on carrier frequency was AGS. Novel variants were discovered in 51% of the cases, but 49% possessed previously reported variants. Missense variants were high in number and accounted for 73% of all cases. Compared with other disorders, MLD due to saposin b deficiency was more common than expected, Pelizaeus-Merzbacher-like disease was more prevalent than Pelizaeus-Merzbacher disease, and X-linked adrenoleukodystrophy was less common than expected. The mortality rate among our patients with LD was 24%.Conclusion: To the best of our knowledge, this is the largest cohort of patients with LD from Saudi Arabia. We present epidemiological, clinical, radiological, and genetic data. Furthermore, we report 18 variants that have not been reported previously. These findings are of great clinical and molecular utility for diagnosing and managing patients with LD.

Deep intronic deletion in intron 3 of PLP1 is associated with a severe phenotype of Pelizaeus-Merzbacher disease

Recently, altered PLP1 splicing was confirmed as a genetic cause of hypomyelination of early myelinating structures (HEMS). A novel deep intronic deletion in intron 3 of PLP1 (NM_000533.5: c.453+59_+259del) was identified, and an in vitro minigene assay detected abnormal splicing patterns. However, the clinical and radiological findings of the patient were compatible with a severe phenotype of Pelizaeus-Merzbacher disease rather than HEMS, which may be due to undetected abnormal PLP1 splicing.

Hypomyelinating Leukodystrophy 15 (HLD15)-Associated Mutation of EPRS1 Leads to Its Polymeric Aggregation in Rab7-Positive Vesicle Structures, Inhibiting Oligodendroglial Cell Morphological Differentiation

Pelizaeus–Merzbacher disease (PMD), also known as hypomyelinating leukodystrophy 1 (HLD1), is an X-linked recessive disease affecting in the central nervous system (CNS). The gene responsible for HLD1 encodes proteolipid protein 1 (plp1), which is the major myelin structural protein produced by oligodendroglial cells (oligodendrocytes). HLD15 is an autosomal recessive disease affecting the glutamyl-prolyl-aminoacyl-tRNA synthetase 1 (eprs1) gene, whose product, the EPRS1 protein, is a bifunctional aminoacyl-tRNA synthetase that is localized throughout cell bodies and that catalyzes the aminoacylation of glutamic acid and proline tRNA species. Here, we show that the HLD15-associated nonsense mutation of Arg339-to-Ter (R339X) localizes EPRS1 proteins as polymeric aggregates into Rab7-positive vesicle structures in mouse oligodendroglial FBD-102b cells. Wild-type proteins, in contrast, are distributed throughout the cell bodies. Expression of the R339X mutant proteins, but not the wild-type proteins, in cells induces strong signals regulating Rab7. Whereas cells expressing the wild-type proteins exhibited phenotypes with myelin web-like structures bearing processes following the induction of differentiation, cells expressing the R339X mutant proteins did not. These results indicate that HLD15-associated EPRS1 mutant proteins are localized in Rab7-positive vesicle structures where they modulate Rab7 regulatory signaling, inhibiting cell morphological differentiation. These findings may reveal some of the molecular and cellular pathological mechanisms underlying HLD15.

Novel insight into the potential pathogenicity of mitochondrial dysfunction resulting from PLP1 duplication mutations in patients with Pelizaeus–Merzbacher disease

Among the hypomyelinating leukodystrophies, Pelizaeus–Merzbacher disease (PMD) is a representative disorder. The disease is caused by different types of PLP1 mutations, among which PLP1 duplication accounts for ~ 70% of the mutations. Previous studies have shown that PLP1 duplications lead to PLP1 retention in the endoplasmic reticulum (ER); in parallel, recent studies have demonstrated that PLP1 duplication can also lead to mitochondrial dysfunction. As such, the respective roles and interactions of the ER and mitochondria in the pathogenesis of PLP1 duplication are not clear. In both PLP1 patients’ and healthy fibroblasts, we measured mitochondrial respiration with a Seahorse XF Extracellular Analyzer and examined the interactions between the ER and mitochondria with super-resolution microscopy (spinning-disc pinhole-based structured illumination microscopy, SD-SIM). For the first time, we demonstrated that PLP1 duplication mutants had closer ER-mitochondrion interfaces mediated through structural and morphological changes in both the ER and mitochondria-associated membranes (MAMs). These changes in both the ER and mitochondria then led to mitochondrial dysfunction, as reported previously. This work highlights the roles of MAMs in bridging PLP1 expression in the ER and pathogenic dysfunction in mitochondria, providing novel insight into the pathogenicity of mitochondrial dysfunction resulting from PLP1 duplication. These findings suggest that interactions between the ER and mitochondria may underlie pathogenic mechanisms of hypomyelinating leukodystrophies diseases at the organelle level.

Pelizaeus-Merzbacher Disease with Novel Variant: Case Report

Context: Pelizaeus-Merzbacher Disease (PMD) is a rare X-linked recessive hypomyelinating leukodystrophy caused by mutations in the proteolipid protein 1 (PLP1) gene, associated with myelin sheath development and stability. The result is a broad spectrum of clinical phenotypes. Diagnosis is confirmed by genetic testing. Clinical features include hypotonia followed by progressive spasticity, nystagmus, ataxia and cognitive impairment. Males are more affected. Females are asymptomatic or present milder symptoms. Most cases arise from duplications, point and null mutations. Null mutations are associated with milder phenotypes. Brain Magnetic Resonance Imaging (MRI) may reveal hypomyelination. There is no disease modifying treatment for PMD. We aim to present the case of a woman with a novel variant of the PLP1 gene. Case report: A 38-year-old female presented with 23 years of progression of upper limb tremor, speech impairment, lower limb rigidity and urinary incontinence. She reported abnormal development of reading and writing skills. She had a brother with cognitive impairment, delayed motor development, gait disorder and generalized tonic-clonic seizures; and a sister with upper limb tremor, dysarthria and behavioral disorder. Hypomyelination was detected on brain MRI. Complete exome sequencing detected a novel likely pathogenic variant of PLP1 gene: ChrX(GRCh37):NC_000023.10:g.103041651del:NM _000533.3:c449del, p.Asp150AlafsTer10, heterozygous. Conclusions: The patient’s case resembles a milder form of PMD. This is supported by literature linking deletions and female sex to milder phenotypes. In 20 to 40% of cases with suggestive clinical findings, no PLP1 mutation is found. New studies are needed to identify other variants associated with PMD.