[The hereditary vessel disease CADASIL].

Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) is a hereditary small vessel disease of the brain characterized by progressive white matter lesions, subcortical infarcts, and cognitive decline. This autosomal dominant disorder is caused by mutations in the NOTCH3 gene located on chromosome 19, resulting in the accumulation of granular osmiophilic material within the walls of small arteries and arterioles. Clinically, CADASIL typically manifests in mid-adulthood with recurrent ischemic events, migraine with aura, mood disturbances, and cognitive impairment. Neuroimaging plays a crucial role in the diagnosis of CADASIL, with characteristic findings including white matter hyperintensities particularly in the anterior temporal lobe and external capsule.

Perinatal risk factors for SUDEP: A population-based case-control study.

Sudden unexpected death in epilepsy (SUDEP) is a leading epilepsy-related cause of death. Researchers have highlighted the similarities between SUDEP and sudden infant death syndrome (SIDS), but perinatal risk factors such as those identified for SIDS have not been assessed previously for SUDEP. We conducted a population-based case-control study of 58 SUDEP individuals and 384 living epilepsy controls born after 1982, utilizing the Swedish Medical Birth Register together with other national health registers and individual medical records to examine if prenatal and perinatal factors are associated with SUDEP risk. We observed a 3-fold SUDEP risk increase for infants who were small for gestational age (SGA) (odds ratio [OR] 3.13; 95% confidence interval [CI] 1.05-9.30) and for those with an Apgar score of 0-6 compared to 9-10 at 10 min (OR 3.22; 95% CI 1.05-9.87). After adjusting for a number of known SUDEP risk factors, we observed that the Apgar score between 0 and 6 after 10 min had a 10-fold increased risk for SUDEP OR 10.37 (95% CI 1.49-72.01) and over a 2-fold risk for those born after the 40th gestational week (OR 2.42; 95% CI 1.03-5.65). The potential mechanisms linking low Apgar score, gestational age, and SGA to SUDEP risk remain to be explored.

[Transient Global Amnesia in the Reykjavik area].

BACKGROUND: Transient Global Amnesia (TGA) is a benign syndrome characterized by sudden anterograde memory loss, that resolves spontaneously within 24 hours. TGA appears without other focal neurological symptoms. The aim of this study was to study TGA in the greater Reykjavik-area. METHODS: We retrospectively analysed the medical history of patients with a diagnosis of TGA (ICD-10 G45.4) at the University Hospital in Iceland in 2010-2021. Medical records were reviewed, and information about year and age at diagnosis, sex, symptoms, precipitating events, imaging results and risk factors were collected. Statistical processing was performed with Excel and Rstudio. RESULTS: Overall, 348 attacks of TGA were identified with a mean frequency of 29 attacks/year, where 9.9% had an earlier history of TGA. The mean age was 64.1, with 50% of subjects between 58-70 years old. The sex distribution was equal (49.9% female). Possible precipitating events were found in 53.7% of cases, with physical activity being the most common one (24.4%), followed by sudden temperature change and emotional stress. In 96% of patients a computerized tomography was performed (no sign of acute changes were found), and magnetic resonance imaging (MRI) in 36.2% of cases. MRI showed restricted diffusion in the hippocampal area in 10.3% of cases. DISCUSSION: TGA is not a rare but a benign syndrome. Our findings regarding age, sex distribution and precipitating events were in accordance with other studies. TGA is thought to result from a temporary hippocampal dysfunction supported by the clinical presentation and MRI findings. The cause of TGA is however still unknown.

[The incidence of sinus thrombosis in Iceland 2008-202].

BACKGROUND: Cerebral venous sinus thrombosis (CSVT) is the cause of 0.5%-1% of all strokes. CSVT can cause haemorrhage, cerebral infarction and increased intracranial pressure. Due to a variety of symptoms, CSVT can be difficult to diagnose. The purpose of this study was to examine the incidence of CSVT in Iceland 2008-2020, risk factors, symptoms, treatment and outcome. METHODS: A retrospective reviewing of medical records of those diagnosed with CSVT from 1. January 2008 to 31. December 2020, was performed. Sex, age at diagnosis, symptoms, known risk factors, imaging results, treatment and outcome were studied. Statistical processing was performed with Excel and Rstudio. RESULTS: Overall, 31 patients were diagnosed with CSVT (22 women). The mean incidence was 0.72/100.00 per year. The mean age was 34.3 years (14-63 years). The most common symptom was headache (87%), other symptoms included focal symptoms and seizures. The most common risk factor was the use of oral contraceptives (73%). Four patients had no risk factor. The most commonly affected sinus was the transverse-sinus (74%). All patients were treated with anticoagulants. Most received heparin or low-molecular-weight heparin then succeeded by warfarin or NOACs. Three months after diagnosis, 87% of the patients scored 0-2 on the modified Rankin Scale. One patient died as a result of CSVT. DISCUSSION: The incidence of CSVT in Iceland is in accordance with other studies. Headache was the most common symptom and oral contraceptives the most common risk factor among women. Most patients made a good recovery, which suggests a timely diagnosis and appropriate treatment for CSVT in Iceland.

[Sudden loss of consciousness due to artery of Percheron infarction].

Acute cerebral infarction due to occlusion of the artery of Percheron (AOP) is rare and poses a diagnostic challenge due to unspecific clinical symptoms. A prompt diagnosis and treatment is vital due to a potentially very serious outcome. Here we represent a healthy young woman who developed sudden headache and loss of consciousness. At admission she was unconscious with GCS of 4, pupils were unevenly dilated and poorly reactive and the plantar reflex was upward bilaterally. She had seizure like movements in all limbs. CT of brain and CT angiography were normal but acute MRI showed bilateral paramedian thalamic diffusion restriction. The patient was treated with i.v. thrombolysis (tPA) 70 minutes after hospital arrival and recovered fully.

[Syndrome of transient headache and neurologic deficits with cerebrospinal fluid lymphocytosis ­ two cases and review]

Here we describe two cases of HaNDL (Headache with Neurological Deficits and cerebrospinal fluid Lymphocytosis). A thirty year old man with episodes of headache with lateralizing symptoms and confusion and a 41 year old man with headache, aphasia and right hemiparesis. Symptoms resolved completely in both patients. Considerable cerebrospinal fluid lymphocytosis was present but no signs of CNS infection and MRIs of the brain were normal. Although the cause of HaNDL is unknown, it is thought to be triggered by a viral infection by some. The prognosis is excellent and symptoms normally resolve within 1-3 weeks. It is important to rule out more serious etiologies like stroke, subarachnoid hemorrhage or central nervous system infections.

Post-stroke epilepsy in an ischemic stroke cohort-Incidence and diagnosis.

OBJECTIVES: Stroke is a common cause of adult-onset epilepsy (post-stroke epilepsy, PSE). Despite an increasing awareness, there is a concern for underdiagnosis of the condition. We aimed to study the adherence to the latest updated epilepsy definition, as well as the incidence and diagnosis of PSE in an ischemic stroke cohort admitted to a tertiary University Hospital. MATERIALS AND METHODS: We retrospectively investigated the occurrence and diagnosis of unprovoked seizures and PSE in all ischemic stroke patients admitted to Karolinska University Hospital in Stockholm during 2015 and registered in the Swedish Stroke Register. Patient records were scrutinized for the presence of post-stroke seizures/epilepsy. RESULTS: A total of 240 patients fulfilling the inclusion criteria were surveyed. Median follow-up time was 1062 days (IQR 589-1195 days). Thirteen patients were diagnosed with PSE according to the study criteria, the incidence of PSE 23/1000 person-years (95% CI 13-38/1000 person-years). Median time to PSE from stroke-onset was 237 days (IQR 33-688). Eleven of 13 PSE patients received an epilepsy diagnosis, eight patients after one unprovoked seizure, and three patients after two. CONCLUSIONS: The majority of PSE patients were given a correct epilepsy diagnosis and treated with antiepileptic drugs. However, this study suggests that there still is potential for improvement in the adherence to the latest updated epilepsy definition. The incidence of PSE in a Swedish ischemic stroke cohort using updated epilepsy definitions is similar to previous studies. Larger studies are needed to confirm our findings on the incidence of PSE.

[MS update: risk factors, diagnosis and treatment]. / Nýjungar í MS: Áhættuþættir, greining og meðferð

Multiple sclerosis (MS) is the most common chronic inflammatory disease of the central nervous system and among the most com-mon causes of neurological disability in young and middle-aged adults. MS is an autoimmune disease caused by a complex interaction between genetic and environmental factors. During the last decades, great advances have been made in understanding the risk factors of MS and the diagnostic ability and treatment of the dis-ease have improved dramatically. It is of importance that doctors are made aware of the possibility of an early diagnosis and effective treatment. In this paper we discuss new knowledge regarding the etiology, diagnosis and treatment of MS.

[Reversible cerebral vasoconstriction syndrome - a common cause of thunderclap headache].

Reversible cerebral vasoconstriction is characterized by thunderclap headache and vasoconstriction of cerebral arteries, with or without focal neurologic symptoms. The syndrome is three times more common in women with a mean age around 45 years. In approximately 60% of cases a cause can be identified, commonly after intake of vasoactive substances. The pathophysiology of reversible cerebral vasoconstriction syndrome is unknown, though temporary dysregulation in cerebral vascular tone is thought to be a key underlying mechanism. The syndrome typically follows a benign course; however, complications such as ischemic stroke or intracranial hemorrhage can cause permanent disability or death in a small minority of patients. Vascular imaging reveals alternating cerebral vasoconstriction and vasodilation that normalizes within 12 weeks. Calcium channel antagonists such as nimodipine reduce the frequency of thunderclap headaches but do not decidedly affect the risk of cerebral ischemia or hemorrhage. In this article the epidemiology, risk factors, pathophysiology, symptoms, diagnosis and treatment of RCVS is reviewed.

Sudden unexpected death in epilepsy. A nationwide population-based study.

OBJECTIVE: The incidence of sudden unexpected death in epilepsy (SUDEP) varies between studies. We determined the incidence of SUDEP in the entire Icelandic population during a 20-year period. METHODS: All individuals in Iceland with epilepsy who died unexpectedly from January 1, 1991 through December 31, 2010 were included. Case ascertainment was based on autopsies, reimbursement for antiepileptic drugs, death certificates, information from neurologists, and medical records. The incidence of SUDEP was calculated according to the total number of residents in Iceland during the study period and an estimated epilepsy population of Iceland. RESULTS: We identified 37 individuals (26 men, 11 women) with definite SUDEP (n = 29), definite SUDEP plus (n = 4), and probable SUDEP (n = 4). Incidence of SUDEP was 0.6 per 100 000 person-years for the general population, and higher among men. The estimated incidence of SUDEP in the epilepsy population was 1.3 per 1000 person-years. SUDEP accounted for 0.1% of all deaths in Iceland during the study period. SIGNIFICANCE: SUDEP is an important cause of death in working-age people. This study provides the incidence of SUDEP in an unselected population of an entire country. The SUDEP incidence in the epilepsy population is comparable to that of previous studies.

Incidence of osmotic demyelination syndrome in Sweden: A nationwide study.

OBJECTIVE: To report the incidence rate of osmotic demyelination syndrome (ODS), associated risk factors, treatment, and long-term outcomes in a nationwide cohort. METHODS: We conducted a retrospective study of individuals diagnosed with central pontine myelinolysis (ICD-10 code G37.2) in the Swedish National Patient Register during 1997-2011. RESULTS: During the study period, we identified 83 individuals with ODS, 47 women and 36 men. Median age at diagnosis was 55 years. The incidence rate of ODS for the entire study period was 0.611 (95% CI: 0.490-0.754) per million person-years and increased during the study period from 0.271 (95% CI: 0.147-0.460) in 1997-2001 to 0.945 (95% CI: 0.677-1.234) individuals per million person-years in 2007-2011. Most cases (86.7%) were hyponatremic with a median sodium level at admission of 104 mmol/L. All hyponatremic cases were chronic. The cause of hyponatremia was multifactorial, including drugs (56.9%), polydipsia (31.9%), and vomiting or diarrhea (41.7%). A majority of patients (69.9%) were alcoholics. Hyponatremic patients were predominantly treated with isotonic saline (93.1%) and only 4.2% with hypotonic fluids. The median correction rate was 0.72 mmol/L/h. Only six patients were corrected in accordance with national guidelines (≤8 mmol/L/24/h). At three months, 7.2% had died and 60.2% were functionally independent (modified Rankin Scale 0-2). INTERPRETATION: We found an increasing incidence during the study period, which could partly be explained by increased access to magnetic resonance imaging. ODS occurs predominantly in patients with extreme chronic hyponatremia which is corrected too fast with isotonic saline. Most patients survived and became functionally independent.

Evolution over time of SUDEP incidence: A nationwide population-based cohort study.

Prompted by a recent report on declining incidence of sudden unexpected death in epilepsy (SUDEP) following implantation of a vagus nerve stimulator (VNS), we analyzed SUDEP risk over 6 years in a population-based cohort of 60 952 epilepsy patients in Sweden. All deaths from July 1, 2006 through December 31, 2011, were identified. Those with epilepsy mentioned on the death certificate were adjudicated for SUDEP using medical records and autopsy reports. In all, 292 SUDEP cases were identified. Comparing the first years (2006-2007) with the subsequent 4 years (2008-2011), the crude and standardized (to the US 2000 population) incidence of SUDEP (whether or not possible SUDEP was included) was significantly lower during the second time period; Incidence rate ratios based on standardized rates was estimated at 0.76 (95% confidence interval [CI] 0.60-0.97, P = .027) for SUDEP. The incidence of SUDEP decreased by 7% per year during the 6-year follow-up. Our data thus suggest that, for unknown reasons, incidence of SUDEP decreases with duration of follow-up. This has implications for patient counseling as well as for the design of studies attempting to assess the effectiveness of an intervention against SUDEP, which clearly needs to include a control group.

Circumstances of SUDEP: A nationwide population-based case series.

OBJECTIVE: Given the increasing attention being paid to potential strategies for sudden unexpected death in epilepsy (SUDEP) prevention, we analyzed the circumstances of SUDEP and its incidence in relation to time of year, week, and day. METHODS: Prospective case-series based on persons with an International Classification of Diseases (ICD-10) code for epilepsy in the Swedish Patient Registry 1998-2005, who were alive on June 30, 2006 (n = 60 952). Linkage to the National Cause-of-Death Registry identified all deaths from July 2006 through December 2011, with epilepsy mentioned on death certificate, together with all deaths during 2008 (n = 3166). Death certificates, medical charts, autopsy, and police reports were reviewed to identify SUDEP cases and related circumstances. Autopsied non-SUDEP deaths (n = 60) from the study population served as a reference. RESULTS: There were 329 SUDEPs (63% men) of which 167 were definite, 89 probable, and 73 possible. SUDEP cases were younger at death (50.8 years) than non-SUDEP deaths (73.3 years) (P < .001) and more likely to be male (63% vs 55%, P = .0079). Most SUDEP cases died at night (58%), at home (91%), and 65% were found dead in bed. When documented, 70% were found in prone position. In 17%, death was witnessed and in 88% of these, a seizure was observed. Of the 329 SUDEP cases, 71% were living alone and 14% shared a bedroom. Compared to an autopsied non-SUDEP reference group, definite SUDEPs were more likely to die at home, during the night, unwitnessed, in the prone position, to live alone, and more often with a preceding seizure. SIGNIFICANCE: SUDEP cases live alone, die unwitnessed at home at night, with indication of a preceding seizure, supporting the critical role of lack of supervision. These facts need to be considered in the development of preventive strategies.

Long-term control and predictors of seizures in intracranial meningioma surgery: a population-based study.

BACKGROUND: The aim of this retrospective study was to investigate the long-term seizure control and antiepileptic drug (AED) prescriptions, as well as identifying predictors of seizure(s) before and after surgery in a population-based cohort of operated intracranial meningioma patients. METHODS: A total of 113 consecutive adult (> 18 years old) patients with newly diagnosed meningioma operated at the Karolinska University Hospital between 2006 and 2008 were included and followed up until the end of 2015. Data on seizure activity and AED prescriptions were obtained through chart review and telephone interview. Logistic regression and survival analysis were applied to identify risk factors for pre- and postoperative seizures. RESULTS: A total of 21/113 (18.6%) patients experienced seizures before surgery of which 8/21 (38.1%) went on to become seizure-free after surgery. Thirteen (14%) patients experienced new-onset seizures after surgery. The regression analysis revealed tumor diameter ≥ 3.5 cm as a risk factor for preoperative seizures (OR 3.83, 95% CI 1.14-12.87). Presence of headache (OR 0.19, 95% CI 0.05-0.76) and skull base tumor location (OR 0.14, 95% CI 0.04-0.44) decreased the risk of preoperative seizures. Postoperative seizures were associated with tumor diameter ≥ 3.5 cm (OR 2.65, 95% CI 1.06-6.62) and history of preoperative seizures (OR 3.50, 95% CI 1.55-7.90). CONCLUSION: Seizures are common before and after intracranial meningioma surgery. Approximately one third of patients with preoperative seizures become seizure-free on long-term follow-up after surgery, while 14% experienced new-onset seizures after surgery. Larger tumor size, absence of headache, and non-skull base location were associated with preoperative seizures, while tumor size and preoperative seizures were associated with postoperative seizures.

Intracranial meningiomas and seizures: a review of the literature.

BACKGROUND: Seizures are a common manifestation of brain tumors, but literature on the incidence of seizures before and after surgery for meningiomas is limited, and principles for use of antiepileptic drugs (AEDs) are controversial. METHODS: This review is based on a MEDLINE search for articles from 1994 to 2014 describing intracranial meningioma and seizures or epilepsy, and AEDs treatment during and after surgery. RESULTS: Up to 40 % of patients with symptomatic meningiomas present with seizures before operation. Tumor removal usually results in seizure control, but around 20 % of patients continue to have or develop new-onset seizures after surgery. Risk factors for seizures after surgery include preoperative seizures, tumor location, and extent of tumor removal. There are no solid data to support routine pre- or postoperative AED prophylaxis in seizure-free patients, and the decision to treat and the selection of AEDs should follow the general principles of treatment of focal epilepsies. CONCLUSIONS: Seizures are a common manifestation of meningiomas, but about 80 % patients with preoperative seizures can be seizure free after tumor removal. Prospective controlled AED trials specifically on meningioma patients are much needed.

Long-term use of rituximab increases T cell count in MS patients.

Rituximab has been used to treat MS patients in Iceland for over a decade. However, long-term effect of rituximab on leukocyte populations has not yet been elucidated. By retrospective analysis of flow cytometric data from 349 patients visiting the neurological ward at The National University Hospital of Iceland from 2012 to 2023 for rituximab treatment, the long-term effect of rituximab and whether the effect was dose dependent (1000mg vs 500mg) was evaluated. No difference was detected in efficacy of B cell depletion in patients treated with 500mg as an initial dose of rituximab when compared to 1000mg. Long-term use of rituximab led to an increase in T cell count (p=0,0015) in patients receiving 3-8 doses of rituximab (1.5-8 years of treatment). The increase occurred in both CD4+ (p=0,0028) and CD8+ T cells (p=0,0015) and led to a decrease in the CD4/CD8 ratio (p=0,004). The most notable difference lies in reshaping the balance between näive and effector CD8+ T cells. The clinical implications of long-term treatment with rituximab and its effect on the T cell pool needs to be explored further. Since no difference in B cell depletion was detected between the two patient groups, 1000mg as an initial dose might be excessive, suggesting a personalized dosing regimen might have therapeutic and financial advantages.

Type, Etiology, and Duration of Epilepsy as Risk Factors for SUDEP: Further Analyses of a Population-Based Case-Control Study.

BACKGROUND AND OBJECTIVES: We conducted a nationwide case-control study in Sweden to investigate the risk of sudden unexpected death in epilepsy (SUDEP) in relation to epilepsy duration, epilepsy type, and etiology in combination with occurrence and frequency of tonic-clonic seizures (TCS) and nocturnal TCS. METHODS: The study comprised 255 SUDEP cases and 1,148 epilepsy controls. Clinical information was obtained from medical records. The association between SUDEP and risk factors was estimated by odds ratios (ORs) with 95% CIs calculated by conditional logistic regression to account for matching by sex and calendar time. RESULTS: The risk of SUDEP was elevated in people with focal (OR 1.48, 95% CI 1.00-2.20), generalized and focal (OR 3.51, 95% CI 1.55-7.96), or unknown (OR 2.43, 95% CI 1.29-4.57) vs generalized epilepsy type. Increased risk of SUDEP was also observed in relation to epilepsy with traumatic causes (OR 2.27, 95% CI 1.33-3.89 vs genetic etiology) or short duration (OR 1.71, 95% CI 1.01-2.87 for 0-5 vs 6-15 years duration). Among those with 1-3 TCS during the preceding year, structural epilepsy etiology was associated with a more than 10-fold increase 10.84 (4.85-24.27) in SUDEP risk compared with people with genetic epilepsy without TCS. The risk with ≥4 TCS the preceding year was similar among those with generalized and focal epilepsies. Those with ≥4 TCS had an OR of 210.73 (95% CI 28.40-∞) during years 0-5 compared with those free from TCS and an epilepsy duration of 6-15 years. The combination of short epilepsy duration (0-5 years) and nocturnal TCS conferred an OR of 45.99 (95% CI 12.19-173.61) compared with having longer duration (6-15 years) and being free from nocturnal TCS. DISCUSSION: Although certain etiologies, such as post-traumatic epilepsy, seem to entail a higher SUDEP risk, our data indicate that frequent and nocturnal TCS carry a similar level of risk whether focal or generalized from onset. The tonic-clonic part of the seizure seems to be decisive for the fatal outcome. SUDEP risk associated with TCS is highest during the first years after the epilepsy diagnosis which calls for effective TCS treatment and vigilance from the onset of diagnosis.

Long-term Outcomes After Periprocedural and Spontaneous Spinal Cord Infarctions: A Population-Based Cohort Study.

BACKGROUND AND OBJECTIVES: Spinal cord infarction (SCInf) is a rare condition where consensus regarding diagnostic criteria is lacking, and misdiagnosis or delayed diagnosis can be detrimental. The aim of this study was to describe baseline findings and predictors of long-term functional outcome in a population-based cohort of patients with SCInf. METHODS: All adult patients (aged 18 years or older) treated at the spinal cord injury unit of the study center, between 2006 and 2019, and discharged with a G95 diagnosis (other and unspecified disease of the spinal cord) were screened for inclusion. The diagnostic criteria proposed by Zalewski et al. were retrospectively applied to evaluate the certainty of the SCInf diagnosis. RESULTS: A total of 270 patients were screened and 57 were included in the study, of whom 30 had a spontaneous SCInf and 27 had a periprocedural SCInf. The median American Spinal Cord Injury Association Impairment Scale (AIS) on admission was C, which at a median follow-up of 2.1 years had improved to D (p = 0.002). Compared with periprocedural cases, those with spontaneous SCInf showed significantly better admission AIS (median AIS D vs B, p < 0.001), fewer multilevel SCInf (27% vs 59%, p = 0.029), shorter hospital stay (median 22 vs 44 days, p < 0.001), and better AIS (median AIS D vs C, p < 0.001) and ambulatory status on long-term follow-up (66% vs 1%, p < 0.001). Regression analyses revealed that spontaneous SCInfs (odds ratio [OR] 5.91 [1.92-18.1], p = 0.002) and more favorable admission AIS (OR 33.6 [7.72-146], p < 0.001) were significant predictors of more favorable AIS at follow-up, with admission AIS demonstrating independent predictive ability (OR 35.9 [8.05-160], p < 0.001). DISCUSSION: SCInf is a rare neurologic emergency lacking specific management guidelines. While the presumptive diagnosis is based on the typical presentation and clinical findings, T2-weighted and diffusion-weighted MRI were the most useful diagnostic tools in establishing a definitive diagnosis. Our data show that spontaneous SCInf mostly affected a single spinal cord segment, whereas periprocedural cases were more extensive, had poorer AIS on admission, poorer ambulatory function, and longer hospital stays. Regardless of the etiology, significant neurologic improvements were seen at long-term follow-up, highlighting the importance of active rehabilitation.

An unusually low prevalence of Huntington's disease in Iceland.

OBJECTIVES: Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by involuntary movements and psychiatric disturbances, found worldwide, with a variable prevalence. The purpose of this study was to determine the history of HD in Iceland and determine the prevalence and incidence of HD. MATERIALS AND METHODS: Clinical information was obtained from general, neurologic, and psychiatric hospitals, practicing neurologists, general practitioners, and family members of affected individuals. RESULTS: Twenty-seven individuals were identified with typical symptoms of HD from the 1850s to 2007. All but one sporadic case are descendants of a husband and wife living in the early and mid-19th century. The point prevalence of HD in Iceland is 1.0 per 100,000 individuals. CONCLUSIONS: The prevalence of HD in Iceland is markedly lower than in the neighboring countries (Norway and the British Isles), where Icelanders originate from.