Clinicopathologic correlation and pathogenesis of ocular and central nervous system manifestations in Hallervorden-Spatz syndrome

Neurodegeneration with Brain Iron Accumulation Disorders and Retinal Neurovascular Structure

BACKGROUND

The unique neurovascular structure of the retina has provided an opportunity to observe brain pathology in many neurological disorders. However, such studies on neurodegeneration with brain iron accumulation (NBIA) disorders are lacking.

OBJECTIVES

To investigate NBIA's neurological and ophthalmological manifestations.

METHODS

This cross-sectional study was conducted on genetically confirmed NBIA patients and an age-gender-matched control group. The thickness of retinal layers, central choroidal thickness (CCT), and capillary plexus densities were measured by spectral domain-optical coherence tomography (SD-OCT) and OCT angiography, respectively. The patients also underwent funduscopy, electroretinography (ERG), visual evoked potential (VEP), and neurological examination (Pantothenate-Kinase Associated Neurodegeneration-Disease Rating Scale [PKAN-DRS]). The generalized estimating equation model was used to consider inter-eye correlations.

RESULTS

Seventy-four patients' and 80 controls' eyes were analyzed. Patients had significantly decreased visual acuity, reduced inner or outer sectors of almost all evaluated layers, increased CCT, and decreased vessel densities, with abnormal VEP and ERG in 32.4% and 45.9%, respectively. There were correlations between visual acuity and temporal peripapillary nerve fiber layer (positive) and between PKAN-DRS score and disease duration (negative), and scotopic b-wave amplitudes (positive). When considering only the PKAN eyes, ONL was among the significantly decreased retinal layers, with no differences in retinal vessel densities. Evidence of pachychoroid was only seen in patients with Kufor Rakeb syndrome.

CONCLUSION

Observing pathologic structural and functional neurovascular changes in NBIA patients may provide an opportunity to elucidate the underlying mechanisms and differential retinal biomarkers in NBIA subtypes in further investigations. © 2023 International Parkinson and Movement Disorder Society.

Visual and ocular motor function in the atypical form of neurodegeneration with brain iron accumulation type I

BACKGROUND/AIMS

Neurodegeneration with brain iron accumulation (NBIA) type I is a rare disease that can be divided into a classical or atypical variant, according to age of onset and clinical pattern. Neuro-ophthalmological involvement has been documented in the classical variant but only anecdotically in the atypical variant. We sought to describe the visual and ocular motor function in patients with atypical form of NBIA type I.

METHODS

Cross-sectional study, including patients with genetically confirmed NBIA type I and classified as atypical variant, who underwent ophthalmological examination with best corrected visual acuity (BCVA), optical coherence tomography (OCT), fundus autofluorescence (FAF), electroretinography (ERG), visual evoked potentials (VEP) and video-oculography.

RESULTS

Seven patients with a mean BCVA of 0.12±0.14 logMAR were included. Only two patients showed structural evidence of advanced retinopathy in OCT and FAF, and there were no cases of optic atrophy. ERG data, however, showed abnormal scotopic and/or photopic responses in all patients. VEP were normal in all three patients. Ocular fixation was markedly unstable (eg, increased rate of saccadic pulses) in the majority of patients (5). Additional mild ocular motor disturbances included low gain pursuit (2), hypermetric saccades (1), low gain optokinetic (2) and caloric and rotatory responses (3).

CONCLUSION

Functional retinal changes associated with marked instability of ocular fixation should be included in the clinical spectrum of NBIA, particularly in the atypical form.

Neuro-ophthalmologic and electroretinographic findings in pantothenate kinase-associated neurodegeneration (formerly Hallervorden-Spatz syndrome)

PURPOSE

The onset of pantothenate kinase-associated neurodegeneration (PKAN) occurs in the first and second decade of life and a pigmentary retinal degeneration is a feature of the disorder. Since the neuro-ophthalmologic and electroretinographic (ERG) features have never been well delineated, we describe them in 16 patients with PKAN.

DESIGN

Observational case series.

METHODS

Sixteen patients with genetic and neuroimaging-confirmed PKAN were examined. Ten underwent neuro-ophthalmologic examination and all had ERGs.

RESULTS

Of the 10 who underwent neuro-ophthalmologic examination, all showed saccadic pursuits and eight showed hypometric or slowed vertical saccades. Seven of eight had inability to suppress the vestibulo-ocular reflex; two patients could not cooperate. Two had square wave jerks and four had poor convergence. Vertical optokinetic responses were abnormal in five, and two patients had blepharospasm. Eight patients had sectoral iris paralysis and partial loss of the pupillary ruff consistent with Adie's pupils in both eyes. Only four of 10 examined patients showed a pigmentary retinopathy, but 11 of 16 had abnormal ERGs ranging from mild cone abnormalities to severe rod-cone dysfunction. No patient had optic atrophy. The PANK2 mutations of all of the patients were heterogeneous.

CONCLUSIONS

Adie's-like pupils, abnormal vertical saccades, and saccadic pursuits were very common. These findings suggest that mid-brain degeneration occurs in PKAN more frequently than previously thought. ERG abnormalities were present in approximately 70% and no patient had optic atrophy. Although genotype-ocular phenotype correlations could not be established, allelic differences probably contributed to the variable clinical expression of retinopathy and other clinical characteristics in these patients.

α-Synuclein: Normal Function and Role in Neurodegenerative Diseases

Synucleins are a family of small, highly charged proteins expressed predominantly in neurons. Since their discovery and characterization during the last decade, much has been learned about their structure, potential functions, interactions with other proteins, and roles in disease. One of these proteins, alpha-synuclein (alpha-syn), is the major building block of pathological inclusions that characterize many neurodegenerative disorders, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and neurodegeneration with brain iron accumulation type 1 (NBIA-1), which collectively are termed synucleinopathies. Furthermore, genetic and biological studies support a role for alpha-syn in the pathophysiology of these diseases. Therefore, research must be continued in order to better understand the functions of the synuclein proteins under normal physiological conditions as well as their role in diseases.

Unraveling the Hallervorden-Spatz syndrome: pantothenate kinase-associated neurodegeneration is the name

PURPOSE OF REVIEW

After the recent discovery of the major genetic defect in neurodegeneration with brain iron accumulation (NBIA, formerly Hallervorden-Spatz syndrome), this heterogeneous group of disorders can now be differentiated by clinical, radiographic, and molecular features.

RECENT FINDINGS

Disease caused by mutations in the gene encoding pantothenate kinase 2 (PANK2) is characterized by dystonia and pigmentary retinopathy in children or speech and neuropsychiatric defects in adults, in concert with a specific pattern on MRI of the brain. This virtually pathognomonic radiographic abnormality, called the eye-of-the-tiger sign, comprises hyperintensities within a hypointense medial globus pallidus on T2-weighted images. This disorder is called pantothenate kinase-associated neurodegeneration (PKAN) and accounts for most patients diagnosed with NBIA. Pantothenate kinase is essential to coenzyme A biosynthesis, and PANK2 is targeted to mitochondria, a feature that distinguishes it from the three other human pantothenate kinase homologs. Hypotheses of PKAN pathogenesis are based on the predictions of tissue-specific coenzyme A deficiency and the accumulation of cysteine-containing enzyme substrates, which may chelate iron and lead to the cardinal disease feature of basal ganglia iron accumulation.

SUMMARY

Recent insight into the biochemical basis of PKAN has led to novel ideas for rational therapies. Investigations are under way to enable testing of promising compounds, first in animal models of disease and then in human patients. Identification of the genetic basis for the major form of NBIA has allowed more accurate clinical delineation of the specific diseases that compose this group, a new molecular diagnostic test for PKAN, and hypotheses for treatment of this neurodegenerative disorder.

A novel pantothenate kinase gene (PANK2) is defective in Hallervorden-Spatz syndrome

Hallervorden-Spatz syndrome (HSS) is an autosomal recessive neurodegenerative disorder associated with iron accumulation in the brain. Clinical features include extrapyramidal dysfunction, onset in childhood, and a relentlessly progressive course. Histologic study reveals iron deposits in the basal ganglia. In this respect, HSS may serve as a model for complex neurodegenerative diseases, such as Parkinson disease, Alzheimer disease, Huntington disease and human immunodeficiency virus (HIV) encephalopathy, in which pathologic accumulation of iron in the brain is also observed. Thus, understanding the biochemical defect in HSS may provide key insights into the regulation of iron metabolism and its perturbation in this and other neurodegenerative diseases. Here we show that HSS is caused by a defect in a novel pantothenate kinase gene and propose a mechanism for oxidative stress in the pathophysiology of the disease.

Neurodegeneration with brain iron accumulation, type 1 is characterized by alpha-, beta-, and gamma-synuclein neuropathology

Neurodegeneration with brain iron accumulation, type 1 (NBIA 1), or Hallervorden-Spatz syndrome, is a rare neurodegenerative disorder characterized clinically by Parkinsonism, cognitive impairment, pseudobulbar features, as well as cerebellar ataxia, and neuropathologically by neuronal loss, gliosis, and iron deposition in the globus pallidus, red nucleus, and substantia nigra. The hallmark pathological lesions of NBIA 1 are axonal spheroids, but Lewy body (LB)-like intraneuronal inclusions, glial inclusions, and rare neurofibrillary tangles also occur. Here we show that there is an accumulation of alpha-synuclein (alphaS) in LB-like inclusions, glial inclusions, and spheroids in the brains of three NBIA 1 patients. Further, beta-synuclein (betaS) and gamma-synuclein (gammaS) immunoreactivity was detected in spheroids but not in LB-like or glial inclusions. Western blot analysis demonstrated high-molecular weight alphaS aggregates in the high-salt-soluble and Triton X-100-insoluble/sodium dodecyl sulfate-soluble fraction of the NBIA 1 brain. Significantly, the levels of alphaS were markedly reduced in the Triton X-100-soluble fractions compared to control brain, and unlike other synucleinopathies, insoluble alphaS did not accumulate in the formic acid-soluble fraction. These findings expand the concept of neurodegenerative synucleinopathies by implicating alphaS, betaS, and gammaS in the pathogenesis of NBIA 1.

Intrafamilial phenotypic variability of Hallervorden-Spätz syndrome in a Tunisian family

We report clinical features, CT-scan and MRI findings of three siblings with Hallervorden-Spätz disease, one of them followed for more than 20years. Patient 1 presented at age 10 with progressive generalized dystonia. Five years later she had violent dystonic spasms with opisthotonos and marked oro-mandibular involvement. Later, dystonia stabilized and examination showed dysarthria, multiple deformities related to dystonic posturing, retinal degeneration and no cognitive impairment. Cerebral CT-scan showed bilateral pallidal lucencies and T2 cerebral MRI showed the "eye of the tiger" sign.Patient 2 developed delusions and hallucinations at age 18 with acute phases of hetero-aggressivity diagnosed as "schizophrenic" in a psychiatric hospital. At age 20, he developed oromandibular dystonia, severe dysarthria and epilepsy. Cerebral MRI showed the same "eye of the tiger" sign.Patient 3 presented at age 37 with isolated psychiatric features similar to those of patient 2, also diagnosed "schizophrenic" in a psychiatric hospital. Neurological examination showed mild postural tremor of the hands and intermittent cervical dystonia. He was stabilized with neuroleptic treatment.This family shows marked intrafamilial variability of age at onset, symptom at onset (with "schizophrenic" features unusually described and leading to misdiagnosis), clinical presentation (almost entirely dystonic in one patient and almost entirely psychiatric in two others) and course of the disease (slowly progressive in one sibling, rapidly deteriorating in the second and stabilization in the third). Classification and nosology of subtypes of HSD are discussed.

The nosology of Hallervorden-spatz disease

The development of magnetic resonance imaging has increased the number of clinical and pathological reports of Hallervorden-Spatz disease and Hallervorden-Spatz syndrome. The case-to-case variability is considerable. However, if gene loci and basic pathogenetic mechanisms are to be appreciated, it is imperative that like cases be compared and studied. The designation Hallervorden-Spatz disease should be reserved for the pediatric neurodegenerative disorder, recognizing that it occurs either as a familial or a sporadic disorder. The diagnosis of Hallervorden-Spatz syndrome is non-specific and encompasses a number of distinctive disorders, each having the pallidal triad of iron deposition, axonal spheroids, and gliosis. Clinically or pathologically distinct groups include (a) female patients with dementia, quadriparesis, and neurofibrillary tangles; (b) cases with Lewy bodies; and (c) cases with or without lipid abnormalities which have acanthocytosis and pigmentary retinal degeneration. Adult-onset cases are quite variable, both clinically and pathologically. Iron deposition in the globus pallidus separates these disorders from others in which axonal spheroids occur. Undoubtedly, the pallidal changes are related, some being primary and other possibly epiphenomena. Pathogenetic insights can only be achieved by investigating and comparing like cases.