Sohei Yanagawa

Association of HTRA1 mutations and familial ischemic cerebral small-vessel disease

BACKGROUND The genetic cause of cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL), which is characterized by ischemic, nonhypertensive, cerebral small-vessel disease with associated alopecia and spondylosis, is unclear. METHODS In five families with CARASIL, we carried out linkage analysis, fine mapping of the region implicated in the disease, and sequence analysis of a candidate gene. We also conducted functional analysis of wild-type and mutant gene products and measured the signaling by members of the transforming growth factor beta (TGF-beta) family and gene and protein expression in the small arteries in the cerebrum of two patients with CARASIL. RESULTS We found linkage of the disease to the 2.4-Mb region on chromosome 10q, which contains the HtrA serine protease 1 (HTRA1) gene. HTRA1 is a serine protease that represses signaling by TGF-beta family members. Sequence analysis revealed two nonsense mutations and two missense mutations in HTRA1. The missense mutations and one of the nonsense mutations resulted in protein products that had comparatively low levels of protease activity and did not repress signaling by the TGF-beta family. The other nonsense mutation resulted in the loss of HTRA1 protein by nonsense-mediated decay of messenger RNA. Immunohistochemical analysis of the cerebral small arteries in affected persons showed increased expression of the extra domain-A region of fibronectin and versican in the thickened tunica intima and of TGF-beta1 in the tunica media. CONCLUSIONS CARASIL is associated with mutations in the HTRA1 gene. Our findings indicate a link between repressed inhibition of signaling by the TGF-beta family and ischemic cerebral small-vessel disease, alopecia, and spondylosis.

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy

The clinicopathologic features of two Japanese sisters with cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) are described. Neither patient had a history of hypertension, and both experienced cerebrovascular events before reaching their forties. Severe degenerative changes in the lumbar spine and knee joints were seen on radiographs. MRI showed extensive cerebral white matter lesions, which revealed remarkable arteriosclerotic changes on autopsy.

Progressive decrease in heteronymous monosynaptic la facilitation with human ageing

To evaluate functional change in the spinal reflex pathway with ageing, we studied heteronymous Ia facilitation from the quadriceps to soleus muscle in 30 normal volunteers (aged 24–68 years). The size of the test H-reflex of the soleus muscle was adjusted to 25% that of the maximal M-response. The conditioning stimulus was adjusted to 1.5-fold the motor threshold to stimulate all the Ia fibres in the femoral nerve. Facilitation was quantified as the slope of the very early part of facilitation, within 0.8 ms of onset. This procedure enabled us to evaluate the extent of monosynaptic Ia facilitation without contamination by other effects. The extent of facilitation decreased linearly with age. This decrease in facilitation could reflect a decrease in the number of Ia fibres and in their conduction velocities, and an increase in presynaptic inhibition on Ia terminals. The increase in presynaptic inhibition may be an adaptive phenomenon in the ageing of the neuromuscular system or, alternatively, a deteriorating process with decreasing flexible supraspinal modulation.

Extensive loss of arterial medial smooth muscle cells and mural extracellular matrix in cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL)

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) is a distinctive clinicopathologic entity characterized by young adult‐onset non‐hypertensive vasculopathic encephalopathy accompanied by alopecia and disco‐vertebral degeneration. CARASIL arteriopathy is histopathologically characterized by intense arteriosclerosis without the deposition of granular osmiophilic materials. Until now, the obliterative arteriosclerosis is the presumptive cause of subcortical ischemia in CARASIL; however, a detailed vascular pathology leading to diffuse leukoencephalopathy remains unclear. In this study, we examined two autopsied CARASIL brains in comparison with an autopsy case of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Intensity of arterial sclerotic changes of CARASIL was evaluated by sclerotic index analysis. Immunohistochemical investigations were performed using a battery of primary antibodies, which recognized vascular cellular and extracellular components. As a result, sclerotic changes were disclosed to be mild and infrequent in CARASIL, in contrast to CADASIL that showed severe obliterative arterial changes. In CARASIL, conversely, most of the arteries were centrifugally enlarged and some were collapsed. We further revealed that arterial medial smooth muscle cells (SMCs) in patients with CARASIL were extensively lost, even in arteries without sclerotic changes. Arterial adventitia in CARASIL was conspicuously thin and immunoreactivities for type I, III, and VI collagens and fibronectin were appreciably weak in this region, indicating a reduction in the mural extracellular matrix (ECM). Because of the medial and adventitial degeneration, CARASIL brains likely receive marked fluctuations in blood flow because of deviations in the structural and functional basis of autoregulation mechanisms. We thus consider that diffuse leukoencephalopathy in CARASIL may be caused by arterial medial SMC loss with mural ECM reduction. We speculate that the abnormalities in the ECM are causatively related to the SMC degeneration, since the ECM is a crucial signal determining the biophysiological properties of arterial SMCs.

Cerebral arterial pathology of CADASIL and CARASIL (Maeda syndrome).

Two familial cerebro‐vascular diseases characterized by different cerebral arterial pathologies and presenting in non‐hypertensive young and middle‐aged adults are described. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is characterized by the deposition of smudged periodic acid–Schiff (PAS)‐positive granules known as granular osmiophilic materials (GOM) in the media of small arteries and arterioles. The medial smooth muscle cells are completely lost, and intense adventitial fibrosis is present. Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL), or Maeda syndrome, is characterized by intense arteriolosclerosis without GOM deposition. Fibrous intimal proliferation, hyaline degeneration of the media, thickening and splitting of the internal elastic lamina, and concentric narrowing of the lumen are characteristic features. In PAS preparation, small arteries are occasionally stained homogeneously due to exudative changes, but never exhibit granular appearance in CARASIL (Maeda syndrome). Each of the small arterial changes is intense in the cerebral medullary and leptomeningeal arteries, leading to multifocal, confluent, or diffuse ischemic changes in the cerebrum. The authors suggest that CARASIL be referred to as ‘Maeda syndrome’ or ‘CARASIL (Maeda syndrome)’ to avoid confusion with CADASIL.

Lack of modulation of Ib inhibition during antagonist contraction in spasticity

Objective: To examine the modulation of non-reciprocal group I (Ib) inhibition during tonic contraction of antagonist muscles in patients with spasticity vs normal subjects. Methods: The authors studied 10 patients with spastic paraplegia due to cervical compression myelopathy and 16 age-matched normal subjects. Ib inhibition to soleus motoneurons was recorded as the change in size of the H-reflex of the soleus, evoked by conditioning stimulus to the nerve innervating the medial gastrocnemius muscle. The extent of inhibition was studied at rest and during tonic contraction of the pretibial muscles of variable strength. Results: In the resting state, the extent of inhibition in the patients did not differ from normal controls. During antagonist contraction, the extent of inhibition increased both in the normal subjects and patients. The increment was smaller in the patients, especially in those with severe spastic gait. The smaller increment in the inhibition was correlated with the time required to walk 10 m in the patients. Conclusion: The authors observed a lack of modulation of Ib inhibition during tonic antagonist contraction in patients with spasticity, especially those with gait disturbance. Disturbed central modulation of non-reciprocal (Ib) interneurons may be responsible for spasticity.

Characteristic features and progression of abnormalities on MRI for CARASIL.

Objectives: The objective of this study was to clarify the characteristic brain MRI findings for genetically diagnosed CARASIL (cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy). Methods: Seven patients with CARASIL carrying HTRA1 mutations (representing 6 Japanese families) were included in this study. Eighteen brain MRIs were reviewed and evaluated with a new rating scale based on scoring for abnormal hyperintense lesions and atrophy. Results: At the last follow-up MRI, all patients had hyperintense lesions on T2-weighted images of the frontal white matter, anterior temporal lobe, external capsules, and thalami. Patients with longer time from the onset of cognitive impairment had higher MRI severity score. The atrophy advanced, followed by white matter lesion progression. During the early stage, hyperintense lesions were observed in the frontal white matter, external capsule, and pons. During the late stage, the arc-shaped hyperintense lesion from the pons to the middle cerebellar peduncles, which we designated the “arc sign,” became evident. The arc sign was a characteristic finding for CARASIL in the advanced stage. Conclusions: These characteristic MRI findings for CARASIL are useful for selecting patients for genetic testing. The rating scale correlates well with disease duration and might be useful for assessing disease progression.

Increase in reciprocal Ia inhibition during antagonist contraction in the human leg: a study of motor units and the H reflex.

1. The change in reciprocal Ia inhibition of soleus motoneurones produced by stimulation of the common peroneal nerve was investigated by the use of twenty‐three soleus motor units as well as the soleus H reflex in six normal subjects during tonic pretibial contraction. 2. In the motor unit experiments, motoneuronal excitability was measured as the ‘critical firing stimulus’ (CFS), which is the difference between the test stimulus intensity needed to reach the threshold for the lowest threshold Ia fibres and the intensity which evokes firing of a motor unit with the probability of 50%. The conditioning effect, assessed from the change in the CFS, was expressed as a percentage of the unconditioned CFS. 3. At a conditioning intensity of 0.95 times the motor threshold value, there was Ia inhibition in sixteen of the twenty‐three motor units (69.6%) at rest. Of these sixteen motor units, twelve showed increases in inhibition at intervals below 2.0 ms during pretibial contraction. In four of the remaining seven units, inhibition first appeared during contraction. There was no significant decrease in inhibition at any time during contraction. 4. Based on the conventional H reflex, reciprocal Ia inhibition increased during very weak (below 2% of the maximum) voluntary dorsiflexion and continued to increase at a slightly stronger (3‐8% of the maximum) contraction, then decreased continuously when contraction was strengthened further. Maximal inhibition occurred at a relatively strong contraction when a weak conditioning stimulus was used, and vice versa. 5. We conclude that the activity of reciprocal Ia inhibitory interneurones increases during tonic antagonist contraction. The previous controversy about this inhibition is the result of occlusion at the Ia interneuronal level.

Increase in Ib inhibition by antagonistic voluntary contraction in man.

1. Ib inhibition from gastrocnemius medialis (GM) muscle to soleus (Sol) muscle was studied at rest and at the onset of phasic voluntary contraction of antagonistic pretibial muscles in seventeen normal subjects. 2. In twelve out of seventeen subjects there was inhibition of Sol H reflex by GM conditioning stimulation at rest with a latency of 1.5‐3.0 ms and a threshold of 0.85‐1.00 times the motor threshold (MT). The amount of inhibition at 0.95‐1.05 x MT, which was calculated by subtracting the size of the conditioned reflex from that of the unconditioned one, ranged from 0.8 to 5.6% of the maximal M‐response or 2.9‐18.3% of control H reflex. This inhibition was ascribed to Ib inhibition, taking into account its latency and threshold. 3. On weak pretibial contraction the inhibition either increased in amount or newly appeared in all the subjects. When the strength of voluntary contraction was graded from 1 to 20% of the maximum, the increment in the amount of inhibition decreased or almost disappeared at strengths of more than several per cent. These facts imply that at least some of the Ib interneurones are facilitated to fire by descending commands alone without peripheral Ib impulses. Contralateral ankle dorsiflexion did not modify the inhibition. 4. Soleus muscle H reflex was not modulated at all by cutaneous stimulation instead of GM stimulation at rest, nor was it affected by cutaneous stimulation on ipsilateral antagonistic contraction. 5. It is concluded that activity in the Ib inhibitory pathway is facilitated at the onset of antagonistic voluntary contraction. This suggests that control of the Ib inhibitory pathway may be utilized in ordinary voluntary movement, and is presumably beneficial for smooth execution of movement.

Conditioning effect in single human motoneurones: a new method using the unitary H reflex.

1. A new method for the study of spinal reflexes using single motor units is described. 2. The excitability of a motoneurone is assessed as the ‘critical firing stimulus’ (CFS), which is the difference between the test stimulus intensity needed to reach the threshold for the lowest threshold Ia fibres and the intensity which evokes firing of a motor unit with the probability of 50% (FP50%). The intensity with FP50% is obtained by modulating stimulator output. When the motor unit is fired by a stimulus, the next intensity is decreased, and vice versa. The Ia threshold is defined as the threshold for homonymous monosynaptic peaks in PSTHs during contraction of the muscle examined. 3. A conditioning effect is represented as a change in CFS, the extent being expressed as a percentage of the unconditioned CFS. 4. Effects obtained by conditioning stimulation with the new and conventional H reflex methods are compared. The sensitivities are almost the same and the extents of the effects have highly correlated linear relations for the two methods. 5. The advantages of the new method are (1) that it shows reflex activities on a single motoneurone, (2) that it is applicable both to muscles at rest and during contraction, and (3) that it quantifies conditioning effects as percentages of the size of test Ia EPSPs.