The first Greek case of heterozygous cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy: An atypical clinico-radiological presentation

Abstract

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) was previously considered a rare, early-onset recessive form of small-vessel disease (SVD) caused by biallelic mutations in the serine protease gene HTRA1 with subsequent loss of its activity. However, very recently, there is growing interest of research showing heterozygous HTRA1 mutations as causes of SVD with a dominant inheritance pattern. This first Greek heterozygous CARASIL case with unusual clinico-radiological presentation extends our very recent knowledge on how heterozygous CARASIL mutations may be associated with cerebral SVD. Our findings highlight heterozygous HTRA1 mutations as an important cause of familial SVD, and that screening of HTRA1 should be considered in all patients with a hereditary SVD of unknown aetiology.

Introduction

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) was previously considered a rare recessive form of cerebral small-vessel disease (SVD) due to mutations in the serine protease gene HTRA1 mainly in Asian adults.^1–5 To date, four heterozygous CARASIL non-Asian families have been reported, two of them with Spanish ancestry. Herein, we report the first Greek CARASIL patient with a peculiar phenotype confirmed by molecular analysis that revealed a c.496C > T heterozygous mutation previously reported as homozygous in a Spanish family.⁶

Case report

Α 31-year-old Greek man with a two-year history of migraine without auras presented in our department because of a sudden episode of vertigo followed by total sensorineural hearing loss in left ear. The patient had no history of hypertension, dyslipidaemia or smoking. He was the only offspring born from non-consanguineous parents. His father died at 52 years of age with a history of vascular ischaemic cerebral infarcts. For the previous two decades, his father had developed memory dysfunction. He had also experienced degenerative arthropathy of the knee joints but no lumbago. His brain magnetic resonance imaging (MRI) revealed diffuse leukoencephalopathy (Figure 1(a) and (b)). The patient’s mother died at the age of 47 years with a history of breast cancer.

Figure 1.

(a) and (b) Proband, father’s MRI. FLAIR axial images showing diffuse leukoencephalopathy involving periventricular and deep white matter in both hemispheres and the brain stem, as well as subcortical lesions including the left temporal pole. (c) and (d) MRI of the patient. FLAIR axial images show hyperintense lesions mainly on the corona radiata and the semi-oval centre, which were attributed to chronic small-vessel ischaemia. (e) and (f) FLAIR images at the same levels obtained four years later reveal few new lesions (arrows). (g) Photograph of the patient showing alopecia. (i) Electrophoregram showing a heterozygous mutation, c.496C > T (arrow) Both wild-type and mutant alleles are expressed. MRI: magnetic resonance imaging; FLAIR: fluid-attenuated inversion recovery.

Neurological examination showed bilateral pyramidal signs, including bilateral Hoffmann and Babinski signs and left ankle clonus. He complained of hair loss, starting 10 years prior, but no lumbago. MRI showed fluid-attenuated inversion recovery (FLAIR) hyperintensities (Figure 1(c) and (d)) mainly on the corona radiata and the semi-oval centre, which were attributed to chronic small-vessel ischaemia. FLAIR images at the same levels obtained four years later (Figure 1(e) and (f)) revealed few new lesions. There were no microbleeds on T2* images, or diffusion restriction on either exams (not shown).VEP was normal, and oligoclonal bands in cerebrospinal fluid (CSF) were absent. Serum very-long-chain fatty acids, serum and urine amino acids and leukocyte lysosomal enzymes were all normal. Neuropsychological testing revealed mild cognitive impairment (mini mental status score of 24).

Other underdiagnosed syndromes that mimic migraine and stroke (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes [MELAS]), Fabry disease, rheumatologic diseases and vasculitis were excluded. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) was ruled out by automatic sequencing of exons 2–24 of the NOTCH3 gene. Genetic testing in the European reference laboratory showed heterozygous mutation in the gene HTRA1 (c.496C > T) of our patient. Pathogenity was confirmed in silico analysis using PolyPhen-2, SIFT and MutationTaster prediction tools (Figure 1(i)). The procedures were in accordance with the ethical standards with the Helsinki Declaration of 1975, as revised in 1983, and the patient gave his consent. Unfortunately, as both parents had passed away, no DNA sample was available for the analysis.

Discussion

SVD is a heterogeneous group of disorders leading to strokes, cognitive decline and typical imaging lesions such as small infarctions, microbleeds and macrobleeds.² However, there are various early-onset monogenic forms of SVD, the majority of them with a dominant inheritance pattern in CADASIL patients. By contrast, in CARASIL, as a very rare autosomal recessive form of SVD, 15 heterozygous HTRA1 mutations have been reported as causes of SVD.^7,8 For some of these mutations, dominant-negative HTRA1 or deficient trimer stabilisation mechanisms have been suggested in the pathogenesis of SVD and behave as dominants.^7,8 Our patient’s mutation (also reported by Verdura et al.) is located near Y169 or F171, which are essential for trimer stabilisation.⁹ As Nozaki et al. demonstrated, the artificial HTRA1 mutant Y169E/F171E inhibited form trimers and thus wild-type HTRA1 activity, resulting in a dominant-negative effect on trimerisation. In others mutants, the protease activity did not decrease or was not evaluated (as in our case). Larger studies are required to clarify how these mutants modify HTRA1 function.

Our challenging case extends the so called ‘weak’ phenocopy of CARASIL heterozygous patients.^7,8 These include a later onset of stroke and dementia, lack of spondylosis/alopecia or leukoencephalopathy.^7,8 Migraine, hearing loss, early-onset alopecia and cognitive impairment were found in our patient (Figure 1(g)), while spondylosis and diffuse white-matter abnormalities were absent. The latter, notably, was found in his father, raising doubt on the causality of heterozygous variants carried by this subject. Mild to severe cerebral involvement was evident in the heterozygous asymptomatic parents of two Caucasian patients, suggesting complex intra-familial phenotypic variability.^3,4

Since genotype–phenotype correlation is still very limited, further studies are required to elucidate whether and how heterozygous HTRA1 mutations interact with others factors (e.g. environmental), which other signalling pathways are affected, resulting in symptomatic SVD. This case differs because of very low progression of vanishing white matter at follow-up, suggesting a more complex interrelationship among genetic and environmental components. Overall, these findings highlight the importance in the differential diagnosis of SVD in young patients, particularly with a familial history, even those of non-Asian origin.

Conclusion

This is the first Greek heterozygous CARASIL patient with an unusual clinico-radiological presentation, extending our very recent knowledge on how heterozygous CARASIL mutations may be associated with cerebral SVD. We suggest that screening of HTRA1 should be considered in all patients with a hereditary SVD of unknown aetiology

Funding

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

Conflict of interest

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.