Tadayuki Ishihara

Mosaic Expression of Dystrophin in Symptomatic Carriers of Duchenne's Muscular Dystrophy

A deficiency of the protein dystrophin is known to be the cause of Duchennes muscular dystrophy. To examine the expression of dystrophin in symptomatic female carriers of this X-linked recessive disorder, we performed immunohistochemical studies on muscle-biopsy specimens from three such carriers, using an antiserum raised against a synthetic peptide fragment of dystrophin. In all three carriers, most individual muscle fibers reacted either strongly or not at all to the antiserum for dystrophin; only 2 to 8 percent of fibers showed partial immunostaining. This mosaic staining pattern was present on both cross-sectional and longitudinal muscle specimens. Although the mosaic pattern was seen in all fiber types, more than 80 percent of type 2B and 2C fibers from two of the carriers did not react with the antiserum. Similar studies in nine normal subjects showed consistently strong staining of all muscle fibers. No muscle fibers from 31 patients with Duchennes muscular dystrophy reacted with the antiserum. We conclude that symptomatic carriers of Duchennes muscular dystrophy can be identified by a distinct mosaic pattern in the immunohistochemical staining of the surface membrane of skeletal-muscle specimens. This finding may have practical implications for genetic counseling, although it remains to be shown whether the same staining pattern will be found in muscle specimens from asymptomatic carriers of Duchennes muscular dystrophy.

Immunocytochemical analysis of dystrophin in congenital muscular dystrophy.

Using immunocytochemical methods, we examined the intensity and distribution of dystrophin and spectrin immunostaining of skeletal muscles from 51 congenital muscular dystrophy (CMD) patients including 36 Fukuyama congenital muscular dystrophy (FCMD) and 15 non-FCMD (other CMD). 17 age-matched spinal muscular atrophy (SMA) and 5 Duchenne muscular dystrophy (DMD) patient biopsies were studied as controls. All 15 non-FCMD and SMA patients showed normal localization of dystrophin at the surface membrane of each muscle fiber which was undetectable in DMD. In contrast, 34 of 36 FCMD patients exhibited an unusual immunostaining pattern with occasional (17-43%; mean = 28) negative or abnormally immunoreacted (partially deficient, fluffy or intense) fibers for dystrophin. Dystrophin was absent in 2 of 36 patients having a clinical diagnosis of FCMD, and intragenic deletion of the DMD gene was detected in one. Spectrin, a membrane cytoskeletal protein related to dystrophin, also showed an increased number of abnormally immunostained fibers in FCMD (25%), but not so high in age-matched DMD (9%) or SMA patient muscle (0%). Thus, our results suggested the presence of intrinsic factor(s) that produce abnormality of the plasma membrane of FCMD muscle.

FSHD-like patients without 4q35 deletion

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by progressive weakness and wasting of facial, shoulder-girdle and upper arm muscles. Despite of the characteristic clinical features, the diagnosis of FSHD is sometimes difficult because clinical symptoms are extremely variable including facial sparing type, limb-girdle type, and distal myopathy type. Most of the FSHD patients have a deletion in the subtelomeric region of chromosome 4q35 (FSHMD1A), however the linkage analysis in some families suggested genetic heterogeneity. In the present study, we identified 40 patients without a deletion in the 4q35 region (non-4q35del) among 200 Japanese patients who were clinically suspected to have FHSD. All non-4q35del patients had shoulder-girdle weakness and 75% also had facial weakness. Eight patients showed clinical features that were indistinguishable from FSHD, but two of them had Becker muscular dystrophy. FSHD is clinically, and most likely genetically, as well, variable. Other forms of muscular dystrophy can also mimic FSHD.

Increased expression level of the splicing variant of SIP1 in motor neuron diseases

Survival motor neuron (SMN) interacting protein 1 (SIP1) interacts with SMN protein and plays a crucial role in the biogenesis of spliceosomes. We have identified three novel splicing variants of the SIP1 (SIP1-beta, -gamma and -delta), in addition to the full-length SIP1-alpha. SIP1-alpha as found to be ubiquitously expressed at high levels in the various normal tissues examined. In contrast, SIP1-beta and -gamma were expressed at very low levels in these tissues. In muscle specimens from patients with spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS), the expression of SIP1-alpha was dramatically decreased compared to that observed in the normal tissues. In addition, the expression of SIP1-beta was significantly increased in tissues derived from patients with either disease. These findings suggest that an aberrant alternative splicing event in SIP1 occurs tissues derived from patients with the motor neuron diseases, and contributes to the pathological process of SMA and ALS.

High AMP Deaminase Activity in Rimmed Vacuoles of Skeletal Muscle

Localized high AMP deaminase activity was found in the rimmed vacuoles of skeletal muscles in acid maltase deficiency, distal myopathy with rimmed vacuole formation, and experimental chloroquine myopathy on histochemical staining. Acid phosphatase activity was also increased in and around these vacuoles, but the vacuoles were negative for other histochemical stainings such as with NADH-tetrazolium reductase, ATPase and phosphorylase. These findings suggest that AMP deaminase is bound to membranous components in addition to myosin in skeletal muscle.