Myopathic changes associated with psychomotor delay and seizures caused by a novel homozygous mutation in TBCK.

BACKGROUND: Biallelic mutations in TBC1-domain containing kinase (TBCK) lead to hypotonia, global developmental delay with severe cognitive and motor deficits, and variable presentation of dysmorphic facial features and brain malformations. It remains unclear whether hypotonia in these individuals is purely neurogenic, or also caused by progressive muscle disease. METHODS: Whole exome sequencing was performed on a family diagnosed with nonspecific myopathic changes by means of histological analysis and immunohistochemistry of muscle biopsy samples. RESULTS: A novel homozygous truncation in TBCK was found in two sisters diagnosed with muscle disease and severe psychomotor delay. TBCK was completely absent in these patients. CONCLUSIONS: Our findings identify a novel early truncating variant in TBCK associated with a severe presentation and add muscle disease to the variability of phenotypes associated with TBCK mutations. Inconsistent genotype/phenotype correlation could be ascribed to the multiple roles of TBCK in intracellular signaling and endolysosomal function in different tissues.

Fibrosis and inflammation are greater in muscles of beta-sarcoglycan-null mouse than mdx mouse.

The Sgcb-null mouse, with knocked-down ß-sarcoglycan, develops severe muscular dystrophy as in type 2E human limb girdle muscular dystrophy. The mdx mouse, lacking dystrophin, is the most used model for Duchenne muscular dystrophy (DMD). Unlike DMD, the mdx mouse has mild clinical features and shows little fibrosis in limb muscles. To characterize ECM protein deposition and the progression of muscle fibrosis, we evaluated protein and transcript levels of collagens I, III and VI, decorin, and TGF-ß1, in quadriceps and diaphragm, at 2, 4, 8, 12, 26, and 52 weeks in Sgcb-null mice, and protein levels at 12, 26, and 52 weeks in mdx mice. In Sgcb-null mice, severe morphological disruption was present from 4 weeks in both quadriceps and diaphragm, and included conspicuous deposition of extracellular matrix components. Histopathological features of Sgcb-null mouse muscles were similar to those of age-matched mdx muscles at all ages examined, but, in the Sgcb-null mouse, the extent of connective tissue deposition was generally greater than mdx. Furthermore, in the Sgcb-null mouse, the amount of all three collagen isoforms increased steadily, while, in the mdx, they remained stable. We also found that, at 12 weeks, macrophages were significantly more numerous in mildly inflamed areas of Sgcb-null quadriceps compared to mdx quadriceps (but not in highly inflamed regions), while, in the diaphragm, macrophages did not differ significantly between the two models, in either region. Osteopontin mRNA was also significantly greater at 12 weeks in laser-dissected highly inflamed areas of the Sgcb-null quadriceps compared to the mdx quadriceps. TGF-ß1 was present in areas of degeneration-regeneration, but levels were highly variable and in general did not differ significantly between the two models and controls. The roles of the various subtypes of macrophages in muscle repair and fibrosis in the two models require further study. The Sgcb-null mouse, which develops early fibrosis in limb muscles, appears more promising than the mdx mouse for probing pathogenetic mechanisms of muscle fibrosis and for developing anti-fibrotic treatments. Highlights • The Sgcb-null mouse develops severe muscular dystrophy, the mdx mouse does not. • Fibrosis developed earlier in Sgcb-null quadriceps and diaphragm than mdx. • Macrophages were commoner in mildly inflamed parts of Sgcb-null quadriceps than mdx. • The Sgcb-null model appears more useful than mdx for studying fibrotic mechanisms. • The Sgcb-null model also appears more useful for developing anti-fibrotic treatments.

Familial adult-onset Pompe disease associated with unusual clinical and histological features.

The adult-onset form of Pompe disease had a wide clinical spectrum, ranging from asymptomatic patients with increased CK to muscle cramps and pain syndrome or rigid-spine syndrome. In addition clinical severity and disease progression are greatly variable. We report on a family with 3 siblings characterized by an unusual adult-onset Pompe disease including dysphagia and weakness of tongue, axial and limb-girdle muscles, in association with atypical globular inclusions in muscle fibres. Our study confirms the great clinical and histological variability of adult-onset Pompe disease and further supports the need of careful evaluation of bulbar function in patients affected by this pathology.

Calsequestrin and junctin immunoreactivity in hexagonally cross-linked tubular arrays myopathy.

We report on a patient with muscle pain not associated with muscle weakness. Microscopic examination of the muscle biopsy revealed rod-like cytoplasmic bodies in many fast fibres. By electron microscopy these had a crystalloid structure identical to the hexagonally cross-linked caveolin 3-positive tubular arrays, previously described in patients with similarly benign myopathy. We found that these inclusions were positive for calsequestrin and for the calsequestrin-binding protein junctin, as well as for caveolin 3. However, the genes coding for these proteins were not mutated. For diagnostic purposes calsequestrin and caveolin 3 positivity should be checked when rods are encountered in muscle biopsy for mild myopathy.

Fukutin gene mutations in an Italian patient with early onset muscular dystrophy but no central nervous system involvement.

Hypoglycosylation of alpha-dystroglycan characterizes a subgroup of muscular dystrophies of variable severity, including Fukuyama congenital muscular dystrophy. We found fukutin gene mutations in a 4.5-year-old Italian patient, with reduced alpha-dystroglycan expression, dystrophic features on muscle biopsy, hypotonia since birth, mild myopathy, but no brain involvement. Mutations in the fukutin gene can be associated with much milder phenotypes than classical Fukuyama congenital muscular dystrophy, and, although rare, can occur in non-Japanese.

Neurogenic pain and steroid synthesis in the spinal cord.

The spinal cord (SC) is a biosynthetic center for neurosteroids, including pregnenolone (PREG), progesterone (PROG), and 3alpha/5alpha-tetrahydroprogesterone (3alpha/5alpha-THP). In particular, an active form of cytochrome P450 sidechain cleavage (P450scc) has been localized in sensory networks of the rat SC dorsal horn (DH). P450scc is the key enzyme catalyzing the conversion of cholesterol (CHOL) into PREG, the rate-limiting step in the biosynthesis of all classes of steroids. To determine whether neurosteroidogenesis might be involved in the pivotal role played by the DH in nociception, effects of neurogenic pain provoked by sciatic nerve ligature were investigated on P450scc expression, cellular distribution, and activity in the SC. P450scc mRNA concentration was threefold higher in the DH of neuropathic rats than in controls. The nerve ligature also increased the density of P450sccpositive neuronal perykarya and fibers in the ipsilateral DH. Incubation of spinal tissue homogenates with [3H]CHOL revealed that the amount of newly synthesized [3H]PREG from [3H]CHOLwas 80% higher in the DH of neuropathic rats. Radioimmunoassays showed an increase of PREG and 3alpha/5alpha-THP concentrations in neuropathic rat DH. The upregulation of PREG and 3alpha/5alpha-THP biosynthesis might be involved in endogenous mechanisms triggered by neuropathic rats to cope with the chronic pain state. 3alpha/5alpha-THP formation from PREG can also generate PROG, which decreases sensitivity to pain and protects nerve cells against degeneration. Because apoptotic cell death has been demonstrated in the DH during neuropathic pain, activation of neurosteroidogenesis in spinal tissues might also be correlated to the neuroprotective role of steroids in the SC.

Steroid hormones and growth factors act in an integrated manner at the levels of hypothalamic astrocytes: a role in the neuroendocrine control of reproduction.

Several growth factors (e.g., transforming growth factors beta and alpha, basic fibroblast growth factor), produced by hypothalamic astrocytes, participate in the control of hypothalamic gonadotrophin-releasing hormone (GnRH) neurons. On this basis, we have hypothesized that steroid hormones, like estrogens and progestagens, influence the GnRH neurons by modulating in glial cells the synthesis and the release of these growth factors. Data reported here indicate that the expression of transforming growth factor beta 1 is modulated in hypothalamic astrocytes by a progesterone derivative (i.e., dihydroprogesterone), while estrogens modulate that of basic fibroblast growth factor. Moreover, it is interesting to highlight that the effect of estrogens on basic fibroblast growth factor is mediated by another growth factor (i.e., transforming growth factor alpha). Altogether, the present findings support the concept that steroid hormones and growth factors act in an integrated manner at the level of hypothalamic astrocytes, thus adding a further piece of knowledge in the understanding of the mechanisms controlling GnRH neurons.