Infantile neuroaxonal dystrophy and PLA2G6-associated neurodegeneration: An update for the diagnosis

Infantile Neuroaxonal Dystrophy: Case Report and Review of Literature

Infantile neuroaxonal dystrophy (INAD) is a rare neurodegenerative disorder affecting 1:1,000,000 children. It results from pathogenic variants in the PLA2G6 gene located on chromosome 22q13.1. The onset of symptoms usually occurs between 6 and 18 months, causing developmental regression leading to debilitating symptoms such as muscle weakness, dementia, and loss of basic skills. Eventually, it progresses to life-threatening symptoms, including breathing difficulties, which limit the life expectancy to 5-10 years. While potential genetic therapies for treatment are being developed, they are yet to be approved for use, and management remains essentially supportive. This case report is about a nine-year-old Pakistani girl with INAD. She presented with recurrent chest infections, developmental regression, loss of speech, paralysis, hypertension, and eventually breathing difficulties. Brain magnetic resonance imaging and genetic testing confirmed the diagnosis. This case posed diagnostic challenges in view of its overlapping clinical presentation. Through this report, we aim to raise awareness about this condition among practitioners, outline the importance of genetic counseling in susceptible couples, and suggest potential areas of further research.

Preimplantation genetic testing for monogenic disorders (PGT-M) offers an alternative strategy to prevent children from being born with hereditary neurological diseases or metabolic diseases dominated by nervous system phenotypes: a retrospective study

BACKGROUND

Preimplantation genetic testing for monogenic disorders (PGT-M) is now widely used as an effective strategy to prevent various monogenic or chromosomal diseases.

MATERIAL AND METHODS

In this retrospective study, couples with a family history of hereditary neurological diseases or metabolic diseases dominated by nervous system phenotypes and/or carrying the pathogenic genes underwent PGT-M to prevent children from inheriting disease-causing gene mutations from their parents and developing known genetic diseases. After PGT-M, unaffected (i.e., normal) embryos after genetic detection were transferred into the uterus of their corresponding mothers.

RESULTS

A total of 43 carrier couples with the following hereditary neurological diseases or metabolic diseases dominated by nervous system phenotypes underwent PGT-M: Duchenne muscular dystrophy (13 families); methylmalonic acidemia (7 families); spinal muscular atrophy (5 families); infantile neuroaxonal dystrophy and intellectual developmental disorder (3 families each); Cockayne syndrome (2 families); Menkes disease, spinocerebellar ataxia, glycine encephalopathy with epilepsy, Charcot-Marie-Tooth disease, mucopolysaccharidosis, Aicardi-Goutieres syndrome, adrenoleukodystrophy, phenylketonuria, amyotrophic lateral sclerosis, and Dravet syndrome (1 family each). After 53 PGT-M cycles, the final transferable embryo rate was 12.45%, the clinical pregnancy rate was 74.19%, and the live birth rate was 89.47%; a total of 18 unaffected (i.e., healthy) children were born to these families.

CONCLUSIONS

This study highlights the importance of PGT-M in preventing children born with hereditary neurological diseases or metabolic diseases dominated by nervous system phenotypes.

Phenotype and genotype heterogeneity of PLA2G6-associated neurodegeneration in a cohort of pediatric and adult patients

BACKGROUND

Phospholipase-associated neurodegeneration (PLAN) caused by mutations in the PLA2G6 gene is a rare neurodegenerative disorder that presents with four sub-groups. Infantile neuroaxonal dystrophy (INAD) and PLA2G6-related dystonia-parkinsonism are the main two subtypes. In this cohort, we reviewed clinical, imaging, and genetic features of 25 adult and pediatric patients harboring variants in the PLA2G6.

METHODS

An extensive review of the patients' data was carried out. Infantile Neuroaxonal Dystrophy Rating Scale (INAD-RS) was used for evaluating the severity and progression of INAD patients. Whole-exome sequencing was used to determine the disease's underlying etiology followed by co-segregation analysis using Sanger sequencing. In silico prediction analysis based on the ACMG recommendation was used to assess the pathogenicity of genetic variants. We aimed to survey a genotype-genotype correlation in PLA2G6 considering all reported disease-causing variants in addition to our patients using the HGMD database and the chi-square statistical approach.

RESULTS

Eighteen cases of INAD and 7 cases of late-onset PLAN were enrolled. Among 18 patients with INAD, gross motor regression was the most common presenting symptom. Considering the INAD-RS total score, the mean rate of progression was 0.58 points per month of symptoms (Standard error 0.22, lower 95% - 1.10, and upper 95% - 0.15). Sixty percent of the maximum potential loss in the INAD-RS had occurred within 60 months of symptom onset in INAD patients. Among seven adult cases of PLAN, hypokinesia, tremor, ataxic gate, and cognitive impairment were the most frequent clinical features. Various brain imaging abnormalities were also observed in 26 imaging series of these patients with cerebellar atrophy being the most common finding in more than 50%. Twenty unique variants in 25 patients with PLAN were detected including nine novel variants. Altogether, 107 distinct disease-causing variants from 87 patient were analyzed to establish a genotype-phenotype correlation. The P value of the chi-square test did not indicate a significant relationship between age of disease onset and the distribution of reported variants on PLA2G6.

CONCLUSION

PLAN presents with a wide spectrum of clinical symptoms from infancy to adulthood. PLAN should be considered in adult patients with parkinsonism or cognition decline. Based on the current knowledge, it is not possible to foresee the age of disease onset based on the identified genotype.

A systematic analysis of genotype-phenotype associations with PLA2G6

BACKGROUND

PLA2G6-associated neurodegeneration (PLAN) can be categorized into infantile neuroaxonal dystrophy (INAD), atypical neuroaxonal dystrophy (aNAD), neurodegeneration with brain iron accumulation (NBIA), and early-onset parkinsonism (EOP).

OBJECTIVES

To determine the genotype-phenotype association in PLAN.

METHODS

"PLA2G6" or "PARK14" or "phospholipase A2 group VI" or "iPLA2β" were searched across MEDLINE from June 23, 1997, to March 1, 2023. A total of 391 patients were identified, and 340 patients of them were finally included in the assessment.

RESULTS

The loss of function (LOF) mutation ratios were significantly different (p < 0.001), highest in INAD, followed by NBIA, aNAD, and EOP. Four ensemble scores (i.e., BayesDel, VARITY, ClinPred, and MetaRNN) were assessed to predict the deleteriousness of missense mutations and demonstrated significant differences (p < 0.001). Binary logistic regression analyses demonstrated that LOF mutations were independently associated with brain iron accumulation (p = 0.006) and ataxia (p = 0.025).

CONCLUSIONS

LOF or more deleterious missense mutations are more likely to promote the development of serious phenotype of PLAN, and LOF mutations are independently associated with brain iron accumulation and ataxia.

'Fly-ing' from rare to common neurodegenerative disease mechanisms

Advances in genome sequencing have enabled researchers and clinicians to probe vast numbers of human variants to distinguish pathogenic from benign variants. Model organisms have been crucial in variant assessment and in delineating the molecular mechanisms of some of the diseases caused by these variants. The fruit fly, Drosophila melanogaster, has played a valuable role in this endeavor, taking advantage of its genetic technologies and established biological knowledge. We highlight the utility of the fly in studying the function of genes associated with rare neurological diseases that have led to a better understanding of common disease mechanisms. We emphasize that shared themes emerge among disease mechanisms, including the importance of lipids, in two prominent neurodegenerative diseases: Alzheimer's disease (AD) and Parkinson's disease (PD).

Audiological Findings in Children with PLA2G6-Associated Neurodegeneration

BACKGROUND

 Audiological manifestations of patients with PLA2G6-associated neurodegeneration are limited.

OBJECTIVE

 To analyze the audiological findings in a cohort of 13 children with infantile neuroaxonal dystrophy (INAD).

METHOD

 Patients underwent a battery of audiological tests including tympanometry, distortion product otoacoustic emissions, impedance audiometry, and Brainstem Auditory Evoked Potentials (BAEPs).

RESULTS

 Audiological studies of 13 children indicated sensorineural hearing loss in six children and auditory neuropathy spectrum disorder in four children.

CONCLUSION

 This study may extend the auditory findings for INAD. Additional studies on quality of life and cognitive-brain degeneration related to this disease are required before making appropriate recommendations for aural rehabilitation.

Novel insertion mutation in the PLA2G6 gene in an Iranian family with infantile neuroaxonal dystrophy

Background

Infantile neuroaxonal dystrophy is an autosomal recessive neurological disorder. Individuals with infantile neuroaxonal dystrophy experience progressive loss of vision, mental skills and muscular control, and other variable clinical signs. Pathogenic variants in the PLA2G6 gene, encoding phospholipase A2, are recognized to be the fundamental reason for infantile neuroaxonal dystrophy. This study aimed to detect pathogenic variant in a consanguine Iranian family with infantile neuroaxonal dystrophy.

Methods

The mutation screening was done by whole exome sequencing followed by direct Sanger sequencing.

Results

We identified a homozygous insertion mutation, NM_003560: c.1548_1549insCG (p.G517Rfs*29) in exon 10 of PLA2G6 in the patient. The parents were heterozygous for variant.

Conclusions

Because of the clinical heterogeneity and rarity of infantile neuroaxonal dystrophy, whole exome sequencing is critical to confirm the diagnosis and is an excellent tool for INAD management.

Neurodegeneration with brain iron accumulation: Characterization of clinical, radiological, and genetic features of pediatric patients from Southern India

BACKGROUND

Neurodegeneration with brain iron accumulation (NBIA) is a group of rare inherited neurodegenerative disorders. Ten types of NBIA are known. Studies reporting various NBIA subtypes together are few. This study was aimed at describing clinical features, neuroimaging findings, and genetic mutations of different NBIA group disorders.

METHODS

Clinical, radiological, and genetic data of patients diagnosed with NBIA in a tertiary care centre in Southern India from 2014 to 2020 was retrospectively collected and analysed.

RESULTS

In our cohort of 27 cases, PLA2G6-associated neurodegeneration (PLAN) was most common (n = 13) followed by Pantothenate kinase-associated neurodegeneration (PKAN) (n = 9). We had 2 cases each of Mitochondrial membrane-associated neurodegeneration (MPAN) and Beta-propeller protein- associated neurodegeneration (BPAN) and 1 case of Kufor-Rakeb Syndrome (KRS). Walking difficulty was the presenting complaint in all PKAN cases, whereas the presentation in PLAN was that of development regression with onset at a mean age of 2 years. Overall, 50% patients of them presented with development regression and one-third had epilepsy. Presence of pyramidal signs was most common examination feature (89%) followed by one or more eye findings (81%) and movement disorders (50%). Neuroimaging was abnormal in 24/27 cases and cerebellar atrophy was the commonest finding (52%) followed by globus pallidus hypointensities (44%).

CONCLUSIONS

One should have a high index of clinical suspicion for the diagnosis of NBIA in children presenting with neuroregression and vision abnormalities in presence of pyramidal signs or movement disorders. Neuroimaging and ophthalmological evaluation provide important clues to diagnosis in NBIA syndromes.

Electro-clinical features in epileptic children with chromosome 15q duplication syndrome

OBJECTIVE

We aimed to describe epilepsy and EEG patterns related to vigilance states and age, in chromosome15-long-arm-duplication-syndrome (dup15q) children with epilepsy, in both duplication types: interstitial (intdup15) and isodicentric (idic15).

METHODS

Clinical data and 70 EEGs of 12 patients (5 intdup15, 7 idic15), followed from 4.5 m.o to 17y4m (median follow-up 8y3m), were retrospectively reviewed. EEGs were analyzed visually and using power spectrum analysis.

RESULTS

Seventy video-EEGs were analyzed (1-16 per patient, median 6), follow-up lasting up to 8y10m (median 4y2m): 25 EEGs in intdup15 (8 m.o to 12y.o, median 4y6m) and 45 EEGs in idic15 (7 m.o to 12 y.o, median 15 m). Epilepsy: 6 West syndrome (WS) (2intdup15, 4idic15); 4 Lennox-Gastaut syndromes (LGS) (1 intdup15, 3 idic15), 2 evolving from WS; focal epilepsy (3 intdup15). In idic15, WS displayed additional myoclonic seizures (3), atypical (4) or no hypsarrhythmia (2) and posterior predominant spike and polyspike bursts (4). Beta-band rapid-rhythms (RR): present in 11 patients, power decreased during non-REM-sleep, localization shifted from diffuse to anterior, peak frequency increased with age.

CONCLUSION

WS with peculiar electro-clinical features and LGS, along with beta-band RR decreasing in non-REM-sleep and shifting from diffuse to anterior localization with age are recognizable features pointing towards dup15q diagnosis in children with autism spectrum disorder and developmental delay.

SIGNIFICANCE

This study describes electroclinical features in both interstitial and isodicentric duplications of chromosome 15q, in epileptic children, including some recent extensions regarding sleep features; and illustrates how the temporo-spatial organization of beta oscillations can be of significant help in directing towards dup15q diagnosis hypothesis.

Overdosing on iron: Elevated iron and degenerative brain disorders

IMPACT STATEMENT

Brain degenerative disorders, which include some neurodevelopmental disorders and age-associated diseases, cause debilitating neurological deficits and are generally fatal. A large body of emerging evidence indicates that iron accumulation in neurons within specific regions of the brain plays an important role in the pathogenesis of many of these disorders. Iron homeostasis is a highly complex and incompletely understood process involving a large number of regulatory molecules. Our review provides a description of what is known about how iron is obtained by the body and brain and how defects in the homeostatic processes could contribute to the development of brain diseases, focusing on Alzheimer's disease and Parkinson's disease as well as four other disorders belonging to a class of inherited conditions referred to as neurodegeneration based on iron accumulation (NBIA) disorders. A description of potential therapeutic approaches being tested for each of these different disorders is provided.

Brain MRI Pattern Recognition in Neurodegeneration With Brain Iron Accumulation

Most neurodegeneration with brain iron accumulation (NBIA) disorders can be distinguished by identifying characteristic changes on magnetic resonance imaging (MRI) in combination with clinical findings. However, a significant number of patients with an NBIA disorder confirmed by genetic testing have MRI features that are atypical for their specific disease. The appearance of specific MRI patterns depends on the stage of the disease and the patient's age at evaluation. MRI interpretation can be challenging because of heterogeneously acquired MRI datasets, individual interpreter bias, and lack of quantitative data. Therefore, optimal acquisition and interpretation of MRI data are needed to better define MRI phenotypes in NBIA disorders. The stepwise approach outlined here may help to identify NBIA disorders and delineate the natural course of MRI-identified changes.

Treatment of infantile neuroaxonal dystrophy with RT001: A di-deuterated ethyl ester of linoleic acid: Report of two cases

BACKGROUND

Infantile neuroaxonal dystrophy (INAD) is a rare, autosomal recessive disease due to defects in PLA2G6 and is associated with lipid peroxidation. RT001 is a di-deuterated form of linoleic acid that protects lipids from oxidative damage.

METHODS

We evaluated the pharmacokinetics (PK), safety, and effectiveness of RT001 in two subjects with INAD (subject 1: 34 months; subject 2: 10 months). After screening and baseline evaluations, subjects received 1.8 g of RT001 BD. PK analysis and clinical evaluations were made periodically.

MAIN FINDINGS

Plasma levels of deuterated linoleic acid (D2-LA), deuterated arachidonic acid (D2-AA), D2-LA to total LA, and D2-AA to total AA ratios were measured. The targeted plasma D2-LA ratio (>20%) was achieved by month 1 and maintained throughout the study. RBC AA-ratios were 0.11 and 0.18 at 6 months for subjects 1 and 2; respectively. No treatment-related adverse events occurred. Limited slowing of disease progression and some return of lost developmental milestones were seen.

CONCLUSIONS

Oral RT001 was administered safely in two subjects with INAD. Early findings suggest that the compound was well tolerated, metabolized and incorporated in the RBC membrane. A clinical trial is underway to assess efficacy.

Successful clinical application of pre-implantation genetic diagnosis for infantile neuroaxonal dystrophy

Infantile neuroaxonal dystrophy (INAD) is a rare, lethal, autosomal recessive neurodegenerative disease and leads to progressive impairment of movement and cognition. A couple with a proband child with calcium-independent group VI phospholipase A2 (PLA2G6)-associated INAD and a previous affected pregnancy sought pre-implantation genetic diagnosis (PGD) to bear a healthy child. Intracytoplasmic sperm injection treatment was performed and 15 blastocystic embryos were obtained at days 5 and 6, and these biopsies were amplified. PGD was performed by next-generation sequencing-based linkage analysis in conjunction with aneuploidy screening. Only two embryos were considered for transfer. In the second frozen-thawed embryo transfer cycle, transfer of a mosaic PLA2G6 c.692G>T heterozygous embryo resulted in a singleton ongoing pregnancy. Prenatal diagnosis was performed using amniotic fluid cells, providing results consistent with those of PGD. The aneuploidy screen and karyotype analysis indicated that the chromosomes of the fetus were normal without any mosaicism. The present study reported the first successful PGD for INAD. For parents at risk, this strategy may successfully lead to pregnancies with embryos unlikely to develop INAD, thus providing valuable experience in reproductive management regarding INAD and potentially other single-gene disorders.

iPla2β Deficiency Suppresses Hepatic ER UPR, Fxr, and Phospholipids in Mice Fed with MCD Diet, Resulting in Exacerbated Hepatic Bile Acids and Biliary Cell Proliferation

Background: Group VIA calcium-independent phospholipase A2 (iPla2β) regulates homeostasis and remodeling of phospholipids (PL). We previously showed that iPla2β^-/- mice fed with a methionine-choline-deficient diet (MCD) exhibited exaggerated liver fibrosis. As iPla2β is located in the endoplasmic reticulum (ER), we investigated the mechanisms for this by focusing on hepatic ER unfolded protein response (UPR), ER PL, and enterohepatic bile acids (BA). Methods: Female WT (wild-type) and iPla2β^-/- mice were fed with chow or MCD for 5 weeks. PL and BA profiles were measured by liquid chromatography-mass spectrometry. Gene expression analyses were performed. Results: MCD feeding of WT mice caused a decrease of ER PL subclasses, which were further decreased by iPla2β deficiency. This deficiency alone or combined with MCD downregulated the expression of liver ER UPR proteins and farnesoid X-activated receptor. The downregulation under MCD was concomitant with an elevation of BA in the liver and peripheral blood and an increase of biliary epithelial cell proliferation measured by cytokeratin 19. Conclusion: iPla2β deficiency combined with MCD severely disturbed ER PL composition and caused inactivation of UPR, leading to downregulated Fxr, exacerbated BA, and ductular proliferation. Our study provides insights into iPla2β inactivation for injury susceptibility under normal conditions and liver fibrosis and cholangiopathies during MCD feeding.

PLA2G6-Associated Neurodegeneration (PLAN): Review of Clinical Phenotypes and Genotypes

Phospholipase A2 group VI (PLA2G6)-associated neurodegeneration (PLAN) includes a series of neurodegenerative diseases that result from the mutations in PLA2G6. PLAN has genetic and clinical heterogeneity, with different mutation sites, mutation types and ethnicities and its clinical phenotype is different. The clinical phenotypes and genotypes of PLAN are closely intertwined and vary widely. PLA2G6 encodes a group of VIA calcium-independent phospholipase A2 proteins (iPLA₂β), an enzyme involved in lipid metabolism. According to the age of onset and progressive clinical features, PLAN can be classified into the following subtypes: infantile neuroaxonal dystrophy (INAD), atypical neuroaxonal dystrophy (ANAD) and parkinsonian syndrome which contains adult onset dystonia parkinsonism (DP) and autosomal recessive early-onset parkinsonism (AREP). In this review, we present an overview of PLA2G6-associated neurodegeneration in the context of current research.

Infantile Neuroaxonal Dystrophy: Diagnosis and Possible Treatments

Infantile Neuroaxonal Dystrophy (INAD) is a rare neurodegenerative disease that often cuts short the life span of a child to 10 years. With a typical onset at 6 months of age, INAD is characterized by regression of acquired motor skills, delayed motor coordination and eventual loss of voluntary muscle control. Biallelic mutations in the PLA2G6 gene have been identified as the most frequent cause of INAD. We highlight the salient features of INAD molecular pathology and the progress made in molecular diagnostics. We reiterate that enhanced molecular diagnostic methodologies such as targeted gene panel testing, exome sequencing, and whole genome sequencing can help ascertain a molecular diagnosis. We describe how the defective catalytic activity of the PLA2G6 gene could be potentially overcome by enzyme replacement or gene correction, giving examples and challenges specific to INAD. This is expected to encourage steps toward developing and testing emerging therapies that might alleviate INAD progression and help realize objectives of patient formed organizations such as the INADcure Foundation.

PLA2G6-associated neurodegeneration: Lessons from neurophysiological findings

BACKGROUND AND AIMS

Phospholipase A2 associated neurodegeneration (PLAN) is a heterogeneous autosomal recessive disorder caused by mutations in the ubiquitously expressed PLA2G6 gene. It is responsible for delayed brain iron accumulation and induces progressive psychomotor regression. We report the concomitant clinical, radiological and neurophysiological findings in PLAN patients in an attempt to determine the contribution of each test to guide diagnosis.

METHODS

Concomitant clinical, radiological, electroencephalographic (EEG) and electrodiagnostic testing (EDX) findings in a series of 8 consecutive genetically confirmed PLAN patients were collected.

RESULTS

All patients presented marked motor axonal loss, with decreased or absent distal compound muscle action potentials, acute and chronic denervation at needle electromyography, in contrast with preservation of sensory conduction. EEG showed high-amplitude fast activity in all patients aged above 15 months. Two patients showing severe neonatal hypotonia displayed atypical hypsarhythmia and epileptic spasms. Iron deposition in globus pallidus was observed in only two patients aged above 6 years.

CONCLUSIONS

Peripheral involvement is an early feature in PLAN recognizable by EDX at an earlier stage than typical iron accumulation in the brain. Furthermore, the association of West syndrome and axonal motor neuropathy may represent positive clues in favor of PLAN. This results emphasize the interest of early and repeated EDX.