Masanobu Kinoshita

Abnormal calcium metabolism in myotonic dystrophy as shown by the Ellsworth-Howard test and its relation to CTG triplet repeat length

Abstract Myotonic dystrophy (DM) is an autosomal dominant disorder characterized by peculiar clinical features. Its molecular basis is the unstable expansion of a CTG triplet repeat in the gene encoding myotonin protein kinase (Mt-PK), the nucleotide sequence of which has extensive homology to the cyclic AMP (cAMP)-dependent protein kinase gene. Extensive efforts have been made to clarify the signal transduction pathway in which the responsible gene operates, but confirming evidence has yet to be obtained. Because some symptoms in DM are similar to those in hypoparathyroidism, we divided 24 DM patients into two groups on the basis of their serum calcium levels; Group 1, those with normocalcemia (11 patients), and group 2, those with hypocalcemia (13 patients). The highly sensitive parathyroid hormone (HS-PTH) plasma levels in group 1 were within normal limits, whereas those in group 2 were abnormally high. Laboratory findings for the group 2 patients resembled those for pseudohypoparathyroidism (PHP), whereas those for group 1 patients were normal. The Ellsworth-Howard (EH) test was used to determine which type of PHP the group 2 patients belonged to. Both the phosphaturic (Δ P) and urinary cAMP (UcAMP) responses were estimated. The Δ P responses in group 2 were significantly lower than those in group 1, but their UcAMP responses did not differ. This is evidence that group 2 patients had PHP type II, whereas group 1 patients were normal. We also investigated whether the disease severity differed between the groups. Cataracts, ectopic calcifications, and ossifications, which are associated with PHP, were more frequent in group 2. In addition, the mean IQ in that group was significantly lower. Clinically, the group 2 signs agreed well with those of PHP, whereas for group 1 there was only a slight similarity. These results are additional evidence that the patients in group 2 have abnormal calcium metabolism, the abnormality being in the postadenylate cyclase-cAMP pathway in the renal tubular cells. The degree of (CTG)n expansion, the so-called expanded DNA fragment (EF) size, was determined by standard Southern blot analysis. The allelic EF sizes in both groups were greater than in the healthy controls. Moreover, those in group 2 were significantly longer than those in group 1. We therefore investigated whether EF size is correlated with the serum calcium and plasma PTH levels, the Δ P responses in the EH test, and IQ. All these items were significantly correlated with EF size. Our findings show that the expanded DNA fragment size in DM is correlated with the degree of abnormal calcium metabolism.

Saccadic slowing in myotonic dystrophy and CTG repeat expansion.

Abstract Recent studies have shown that the severity of the several clinical symptoms of myotonic dystrophy (DM) is closely related to the size of a CTG triplet repeat in the gene encoding myotonin protein kinase. Although neurotological findings, including saccadic slowing in patients with DM, have been reported, the relationship between these neurotological findings and elongation of the CTG triplet repeat has not been discussed to our knowledge. We made a case-control study that compared the saccadic velocity in 13 patients with DM and in 13 controls matched for age and sex. We also examined the correlation between the saccadic velocity in DM patients and the size of the expanded DNA fragment (EF) obtained by Southern blot analysis with EcoRI or BglI.We found: (1) The primary eye position was normal in 9 of 12 patients. Divergent strabismus was present in 3 patients. (2) The range of ocular movement was normal in 2 patients, nearly normal in 5 and minimally limited in the other 5. (3) Only 1 patient had lateral gaze nystagmus, which was fine and transient. (4) The horizontal saccades were essentially normometric in 11 of the 13 patients, slightly hypometric in 1 and obviously hypometric in 1. These last 2 patients had the second longest and longest EF sizes. The vertical saccades were essentially normometric in 8 of 12 patients, hypermetric in 3, and hypometric in the 1 with the longest EF size. (5) The saccadic velocity in the DM patients was significantly lower than that in the controls in the horizontal or vertical direction, the difference being more prominent in the horizontal direction. (6) The correlation coefficients between horizontal saccadic velocity and EF size, 0.801 (EcoRI) and 0.756 (BglI), had a strong negative correlation (P < 0.01 for both EcoRI and BglI). No statistically significant correlation was found between vertical saccadic velocity (upward and downward) and EF sizes.Although it was difficult to determine whether saccadic slowing was caused by central oculomotor system involvement or extraocular muscle atrophy, the absence of gaze-evoked nystagmus in almost all of the patients favours the latter.Our study shows that neurotological examinations that include a saccadic velocity test are very useful for detecting subtle eye movement abnormalities in DM and for quantitatively evaluating the clinical severity of DM.

Stapedial reflex in myotonic dystrophy type 1 and CTG repeat expansion

Abstract The severity of clinical symptoms of myotonic dystrophy type 1 (DM1) has been shown to be closely related to the size of a CTG triplet repeat in the gene encoding myotonin protein kinase. Neuro-otological examinations that include eye movement and stapedial reflex (SR) tests can contribute to the quantitative evaluation of muscular involvement in DM1. We previously found that saccadic eye movement velocity in DM1 patients was significantly lower than that in control subjects and that the saccadic velocity and size of the CTG triplet repeat in DM1 patients had a strong inverse correlation. We now report a case-control study that compared the SR wave form (latency: L, contraction time: C50, and relaxation time: D50) measured by the acoustic impedance method in 13 patients with DM1 and in 14 control subjects matched for age and sex. The correlation between the SR wave form and CTG repeat length in DM1 patients obtained by Southern blot analysis with EcoRI was also examined. We found (1) no significant difference between the pure tone audiometric threshold at 500 Hz in the DM1 patients and that in the control subjects; (2) or between the SR thresholds in the patients and controls (500 Hz stimuli); (3) C50 and D50 in DM1 patients to be significantly prolonged, whereas L was not; (4) C50 and D50 in DM1 patients to be significantly correlated with CTG repeat length, whereas L was not. Measurement of SR by the acoustic impedance method is completely non-invasive, causes no discomfort to the subject, and does not depend on the persons effort or cooperation. Our findings show that SR measurement can be used for a quantitative evaluation of muscle involvement in DM1. We believe that the prolongation of D50 in DM1 is caused by myotonia, which has to be confirmed by further clinical and pathological studies.

Molecular analysis of two pre-mutations in myotonic dystrophy.

Here we report two families with myotonic dystrophy (DM) in which the asymptomatic parent proved to be in a pre‐mutation state. Polymerase chain reaction (PCR) analysis of the region spanning the CTG expansion demonstrated that one father of the proband possessed (CTG)n repeats of n = 12 and 44 copies and the other of 15 and 47. Clinical examination showed no definite signs of DM in these two men. Haplotype analysis of DNA markers close to the DM protein kinase (DMPK) gene suggested a common ancestral DM mutation. A continuous gradient of repeat sizes from normal to abnormal range can explain this phenomenon.

A Case of Water Intoxication with Prolonged Hyponatremia Caused by Excessive Water Drinking and Secondary SIADH

Water intoxication is a life-threatening disorder accompanied by brain function impairment due to severe dilutional hyponatremia. We treated a 22-year-old man without psychotic illness who had been put in a detention facility. He drank 6 liters of water over a 3-hour period at the facility as a games penalty, and he showed progressive psychiatric and neurological signs including restlessness, peculiar behavior and convulsions. On his admission, 15 h after the discontinuation of the water drinking, he was in a coma, showing intermittent convulsions and remarkable hyponatremia (120 mmol/l). Because his laboratory tests showed hypertonic urine and normal sodium excretion, the diagnosis of secondary development of syndrome of inappropriate secretion of antidiuretic hormone (SIADH) was strongly suggested and later confirmed by the suppression of the renin-aldosterone system and the inappropriately elevated secretion of ADH. Saline infusion and an initial administration of furosemide in addition to dexamethasone as treatments for the patients brain edema successfully improved his laboratory data and clinical signs by the 3rd hospital day, and he was returned to the facility without physical or psychiatric abnormalities on the 6th day. The secondary SIADH might have been due to the prolonged emesis, recurrent convulsions and rapid elevation of intracranial pressure.

A Case Report of Proliferative Myositis of Bilateral Sternocleidomastoid Muscles.

A case of prolif erative myositis of the bilateral sternocleidomastoid muscle in a 64-year old woman is reported. The patient visited our clinic, complaining of a sore throat and cervical pain, with strong limitation of neck movement, especially backward movement. Physical examination revealed hardness along the bilateral sternocleidomastoid muscles. CT, MRI and Echo imaging studies suggested the presence of pathological lesions in the muscles. Immunochemical examination showed a high level of muscle emzymes, suggesting myositis. The histopathological diagnosis of the excised tissue was proliferative myositis. This disease is a very rare condition, and no case of bilateral myositis has been previously reported in the Japanese literature. We discussed this disease from a clinicopathological viewpoint.