Updated information on the HDLS-S family
The ancestor born in 1857 (I:1 in the pedigree) lived on a farm in an isolated area of Western Sweden. She suffered for 32 years from an undefined mental disorder with “epilepsy” and died from “brain hemorrhage”, but no medical records remain [4]. Of 8 HDLS cases in generations II-III, 5 were documented by relevant diagnostic codes or hospital records from regional psychiatric or geriatric institutions, with HDLS confirmed by histopathology in one (II:8). Three siblings in generation III were examined at our Gothenburg neurology or psychiatry university departments with a preliminary hospital diagnosis of presenile dementia. These 3 cases were the first in whom our clinical, genealogical, and neuropathological examinations defined HDLS (III:20, III:21 and III:22). Individual III:22 had consecutive neurological assessments throughout the course of disease. Two family members in generation III and one in generation IV committed suicide during middle age. Even though the documentation associated with these cases was sparse, we believe these suicidal cases could have been associated with incipient HDLS. One individual (III:19) was established to be a phenocopy [33]. During 2018, we updated the clinical evaluation of the 41 relatives in generation IV to verify the surprisingly low frequency of affected family members now generally above the risk age (present ages ranging from 46 to 85 years). Of these 41 family members 4 died: 2 from histologically verified HDLS (case 1 [IV:33] with neuropathology reported here, and case 2 [IV:36], with neuropathology reported before [33]); 1 allegedly from complications associated with diabetes (IV-5); and 1 from probable suicide in the context of drug abuse (IV-9). For 23 of the 37 family members currently alive, we identified no symptoms or signs of ongoing HDLS disease by personal contact during 2018 usually supported by formal neurological examination performed by the authors CS and OA. Additionally, no symptoms of HDLS were recorded for the remaining healthy family members taking part in this study as reported by close relatives during 2018. The authors followed 3 of these healthy relatives (IV-34, IV-35 and IV-37, children of HDLS affected individuals), by yearly neurological examinations and cerebral MRI during 5–7 years until 2018, all with negative results. In one individual (IV-38), previous publications and assessments suggested HDLS-S, however no disability developed over time. Even though he declined clinical examination, social function was reported to be excellent, indicating the absence of HDLS. One other family member declined to be contacted but was recently reported by relatives to be healthy.
The present study is based on DNA specimens from the 2 affected and 23 unaffected family members in generation IV that were personally followed by the authors (CS and OA), as indicated in Fig. 1.
Case 1
Individual IV-33 in Fig. 1, was previously reported [33, 36]. Briefly, at age 46 this previously healthy manual worker suffered a progressive personality change with striking passivity and loss of responsibility at work and at home. At his first examination half a year after onset we observed a debilitating frontal syndrome with total loss of insight, along with discrete pyramidal and deep sensory signs. During the subsequent 2 years he was in a permanent hyperactive state, incessantly walking, opening cupboards or clapping his hands, still with only moderate motor, sensory and extrapyramidal signs. In the fourth year of his disease he had developed complete hemianopia, and showed gradually increasing rigidity in all extremities, as well as primitive brain stem and grasp reflexes. For 6 years he remained in a vegetative state with a general decortical type of rigidity, a weak doll’s eye reaction and spontaneous respiration of Cheyne-Stokes type until he succumbed from respiratory infections at 57 years of age. Five consecutive MRI examinations up to 26 months disease duration with DTI showed a symmetric leukoencephalopathy with an unusual feature, a progressive rim of decreased diffusion expanding centrifugally through the white matter from the periventricular area of the frontal and occipital horns, leaving apparently disorganized tissue behind the rim [36].
Neuropathology assessment
The brain weighed 1480 g. The leptomeninges were essentially normal and there was no apparent gyral atrophy. There were only minor atheromatous plaques in the extracerebral arteries on the brain surface. Transverse sections of the cerebrum showed extensive liquefaction of the white matter encompassing the centrum semiovale and surrounding the ventricles but sparing a subcortical rim including the arcuate fibers (Fig. 2a). The frontal parts of the temporal lobes were also spared. Corpus callosum and the internal capsule showed the same gelatinous liquified appearance, as well as the entire white matter surrounding the basal ganglia and the thalamus. The pons was flattened and there was a yellowish discoloration of the basal aspect of the lower brain stem corresponding to the pyramidal tracts. The cerebellum showed minor atrophy of the folia and the spinal cord appeared macroscopically normal.
Microscopic examination of the cerebral cortex and underlying white matter showed essentially the same changes in various parts of the brain (Fig. 2). There was no major loss of cortical neurons but some appeared swollen. There were no neurofibrillary tangles or senile plaques as revealed by ubiquitin immunohistochemistry. There was mild gliosis that was variable in different parts of the brain (Fig. 2c) and microglial activation was also seen in the cortex (Fig. 2d). The subcortical white matter was to some extent spared (Fig. 2a-b) but showed accumulation of macrophages and marked gliosis (Fig. 2c). Occasional spheroids could be identified by hematoxylin and eosin staining and by immunohistochemistry for neurofilament protein, however, they were not abundant. The white matter in the border between the partly spared subcortical white matter and the liquified deep parts, showed increased number of cells and frequent corpora amylacea (Fig. 2e), fragmented axons partly with spheroid-like changes (Fig. 2f) and numerous large rounded pigmented macrophages (Fig. 2g-h) with PAS positive and autofluorescent granula (Fig. 2i-j) indicating storage of lipofuscin. Many macrophages included ubiquitinated inclusions. The deep white matter that had undergone severe degeneration with a gelatinous appearance showed sparse cell nuclei.
The white matter of the internal capsule and the pyramidal tracts of the brain stem showed severe loss of myelin and gliosis. The pyramidal tracts showed vascular changes with thickening of the walls and narrow lumina (see below, spinal cord) but no general vasculopathy was observed in the brain.
The basal ganglia and the thalamus appeared reduced in size and there was gliosis but no major reduction in neuronal cell density. Neither was there a major loss of neurons in the cranial nerve nuclei or the inferior olives. In the cerebellum there was a variable loss of Purkinje cells with a concomitant proliferation of Bergmann glia. There was gliosis in the cerebellar white matter and occasional spheroids, but the neurons of the dentate nucleus appeared to be spared. In the spinal cord there was an asymmetric degeneration of the pyramidal tracts affecting both the lateral and anterior cortico-spinal tracts with vascular changes (Fig. 2j-k). The dorsal columns were much less affected. The neurons of the anterior horns were preserved but frequently swollen. The anterior and posterior nerve roots were preserved as was the sciatic nerve.
Case 2
Individual IV-36 in Fig. 1, was previously reported [33]. Briefly, at age 34 this woman, who worked with computer programming, had an insidious onset of cognitive problems followed by increasing sensibility disturbance of her right hand, leading to profound deep sensory ataxia difficult to distinguish from alien hand. In parallel she started to present dystonic and ballistic movements in her extremities, soon compromising her gait. Within months she was wheelchair bound with function loss from multiple cerebral regions, including a general pyramidal syndrome, and complete loss of her inferior visual fields. Two years after onset she was in an uncommunicative state, blind, with short attacks of severe rigidity. Her MRI showed symmetrical changes around the frontal and posterior horns, extending into the parietal centrum semiovale and across the corpus callosum, except for its midportion, also following the corticospinal tracts into the mesencephalon. HDLS was confirmed by characteristic autopsy findings as reported [33].
Genetic analyses
Previous Sanger sequencing of CSF1R coding region in both patients did not identify rare variants predicted to be damaging and that could explain the disease in this family (data not shown). All variants identified in CSF1R by exome sequencing are presented in Additional file 1: Table S1. The analysis of genotyping array data from the CSF1R locus did not reveal any copy number variants (CNVs) that could be involved in the disease either. Similarly, the same analysis at a genome level did not identify CNVs shared by the two affected individuals and that could be considered pathogenic. Exome sequencing analysis revealed that both patients carried variants that were novel, heterozygous, and predicted to be deleterious in two genes associated with the nervous system: NM_001605.2:c.455G > T p.(Cys152Phe) in AARS and NM_024939.3:c.728 T > G p.(Val243Gly) in ESRP2. Both variants were absent in the two healthy relatives. After segregation analysis to validate the association of the variants with the disease, only p.Cys152Phe in AARS remained absent in all the healthy family members tested (Fig. 1 and Additional file 1: Figure S1). This variant is not described in the genome aggregation database (gnomAD), and it was not found in 1000 Swedish individuals [3]. The variant was predicted as damaging by different software: SIFT, PolyPhen-2 and MutationTaster2, and has a high CADD score of 34, suggesting a deleterious effect of the variant in the protein function. It occurs in an evolutionarily conserved amino acid located in the aminoacylation domain of the protein (Fig. 3). Expression analysis at transcript level revealed that both alleles are expressed equally and that no splice defect could be seen (Fig. 3d).