A novel heterozygous HTRA1 mutation in an Asian family with CADASIL‐like disease

Abstract Background HTRA1 gene mutations are related to the pathogenesis of cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL). However, heterozygous HTRA1 mutations at specific sites can also lead to rare autosomal dominant cerebral artery disease (CADASIL‐like disease). To date, 28 heterozygous mutations in the HTRA1 gene have been reported to be related to CADASIL‐like diseases. Only one case of this disease was caused by a heterozygous mutation of c.497G>T in exon 2 of the HTRA1 gene. Methods In this case, we report on an Asian family with CADASIL‐like disease caused by a heterozygous mutation of c.497G>T in exon 2 of the HTRA1 gene. The clinical and imaging characteristics of the proband were summarized, and gene mutations were verified by whole‐exome sequencing (WES) and direct Sanger sequencing. Results The result of the gene sequencing showed a heterozygous missense mutation at the c.497G>T locus of the HTRA1 gene in the proband of one sick family member, resulting in a change in amino acid (p.arg166leu). Conclusion This is the first reported pathogenic mutation at the c.497G>T locus of the HTRA1 gene in an Asian population. It provides an important theoretical basis for the specific gene‐based diagnosis and treatment of CADASIL‐like diseases.

arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL), Fabry disease, retinal vasculopathy with cerebral leukoencephalopathy (RVCL), COL4A1-related diseases, etc. 4 Among the known pathogenic genes of CSVD, the HTRA1 gene is related to the pathogenesis of CARASIL. However, heterozygous HTRA1 mutations at specific sites can also lead to rare autosomal dominant cerebral artery disease (CADASIL-like disease). 5 The HTRA1 gene is located on the long arm of chromosome 10 and consists of nine exons. This gene encodes the synthesis of HTRA serine protease. The encoded protein contains four functional domains and participates in various pathological processes, including arthritis, cancer, cerebrovascular disease, and neurodegenerative diseases. 6 To date, 45 HTRA1 gene mutations related to CSVD have been reported, including 23 types of CADASIL-like diseases caused by heterozygous HTRA1 mutations. Five other types of heterozygous HTRA1 mutations were found to be associated with CARASIL and CADASIL-like disease. 7 There was only one case of CADASIL-like disease caused by c.497G>T heterozygous mutation in exon 2 of the HTRA1 gene which has been reported to date. 5 Herein, we report a case of an Asian family with CADASIL-like disease caused by a c.497G>T heterozygous mutation in exon 2 of the HTRA1 gene. We analyzed the clinical features, imaging features, and gene sequencing results of the proband and drew the disease pedigree map to provide a clinical basis for the diagnosis of this disease.

| Patient and families
We present a patient with CADASIL-like disease, who was admitted to the Department of Neurology, First Affiliated Hospital of Dalian Medical University, China. Peripheral blood samples from the proband (II-1 in Figure 1d) and one sick family member (II-3 in Figure 1d) were collected for investigation. Other immediate relatives of the proband refused the gene detection. The study was approved by the   gene were visualized on a 2% agarose gel. To discover harmful mutations, BLAST (https://blast.ncbi.nlm.nih.gov/) was used to align the sequence data with the HTRA1 reference DNA sequence. 8,9

| Disease history
The proband was a 59-year-old Chinese Han male with intellectual decline, unstable walking, poor urinary control for 6 months, and acute onset weakness of the right lower limb for 1 month. During the course of the disease, symptoms, such as headache, trichomadesis, nausea, vomiting, unclear speech, blurred vision, dysdipsia and dysphagia, limb twitching, dysuria, or unconsciousness, were not present.

| Past history and family history
The proband had a history of cerebral infarction for 2 years. There

| Additional examinations
Head magnetic resonance (MR) showed the following results: (1)

| Genetic analysis
Genomic DNA was extracted from peripheral blood samples of the proband. Spectrophotometric analysis was used to measure the concentration and purity of DNA samples. 10

| DISCUSS ION
The HTRA1 gene mutations often lead to the pathogenesis of CARASIL. Most parents of patients have a history of close relative marriage. It is a non-hypertensive cerebrovascular disease that occurs in youth. Clinically, it is characterized by progressive nervous system damage, including early-onset recurrent stroke, subcortical dementia, affective disorders, gait disorder, and extraneural characteristics, including hair loss and spondylosis. 12 However, heterozygous mutations in the HTRA1 gene also can lead to rare CADASIL-like disease, which is an autosomal dominant disease. Studies found that compared with typical CARASIL, patients with CADASIL-like disease had a later onset age, a higher proportion of vascular risk factors, a lighter and relatively slow clinical progress, and a lower incidence of extraneurological symptoms, such as early-onset spondylosis and hair loss. 7 To date, the pathogenesis of this disease is not fully understood, and there are no special treatment methods. This study focuses mainly on symptomatic support treatment. At the same time, it provides genetic counseling for patients to guide them in avoiding relevant risk factors. It is also recommended to further carry out relevant evaluation and gene screening for the families of patients with a confirmed diagnosis of CSVD caused by genetic variation. 6 With the increasing basic and clinical research on the pathogenesis of this disease and an in-depth understanding of the pathophysiological mechanism, it is necessary to find potential therapeutic targets and provide more theoretical support for its clinical diagnosis and treatment.

| CON CLUS ION
Our findings of a heterozygous c.497G>T mutation in this Asian family provide novel evidence for the HTRA1 mutation in CADASIL-like disease. This finding will improve genetic counseling for both relatives of CARASIL patients and carriers of HTRA1 variants with sporadic CSVD.

ACK N OWLED G M ENTS
We thank the patient for his participation. We thank Editage (www. edita ge.cn) for English language editing.

CO N FLI C T O F I NTE R E S T
The present study does not have any conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data supporting the findings of this study are available from the corresponding author upon reasonable request.