Congenital Titinopathy: Comprehensive characterization and pathogenic insights.

OBJECTIVE: Comprehensive clinical characterization of congenital titinopathy to facilitate diagnosis and management of this important emerging disorder. METHODS: Using massively parallel sequencing we identified 30 patients from 27 families with 2 pathogenic nonsense, frameshift and/or splice site TTN mutations in trans. We then undertook a detailed analysis of the clinical, histopathological and imaging features of these patients. RESULTS: All patients had prenatal or early onset hypotonia and/or congenital contractures. None had ophthalmoplegia. Scoliosis and respiratory insufficiency typically developed early and progressed rapidly, whereas limb weakness was often slowly progressive, and usually did not prevent independent walking. Cardiac involvement was present in 46% of patients. Relatives of 2 patients had dilated cardiomyopathy. Creatine kinase levels were normal to moderately elevated. Increased fiber size variation, internalized nuclei and cores were common histopathological abnormalities. Cap-like regions, whorled or ring fibers, and mitochondrial accumulations were also observed. Muscle magnetic resonance imaging showed gluteal, hamstring and calf muscle involvement. Western blot analysis showed a near-normal sized titin protein in all samples. The presence of 2 mutations predicted to impact both N2BA and N2B cardiac isoforms appeared to be associated with greatest risk of cardiac involvement. One-third of patients had 1 mutation predicted to impact exons present in fetal skeletal muscle, but not included within the mature skeletal muscle isoform transcript. This strongly suggests developmental isoforms are involved in the pathogenesis of this congenital/early onset disorder. INTERPRETATION: This detailed clinical reference dataset will greatly facilitate diagnostic confirmation and management of patients, and has provided important insights into disease pathogenesis. Ann Neurol 2018;83:1105-1124.

Recessive myosin myopathy with external ophthalmoplegia associated with MYH2 mutations.

Myosin myopathies comprise a group of inherited diseases caused by mutations in myosin heavy chain (MyHC) genes. Homozygous or compound heterozygous truncating MYH2 mutations have been demonstrated to cause recessive myopathy with ophthalmoplegia, mild-to-moderate muscle weakness and complete lack of type 2A muscle fibers. In this study, we describe for the first time the clinical and morphological characteristics of recessive myosin IIa myopathy associated with MYH2 missense mutations. Seven patients of five different families with a myopathy characterized by ophthalmoplegia and mild-to-moderate muscle weakness were investigated. Muscle biopsy was performed to study morphological changes and MyHC isoform expression. Five of the patients were homozygous for MYH2 missense mutations, one patient was compound heterozygous for a missense and a nonsense mutation and one patient was homozygous for a frame-shift MYH2 mutation. Muscle biopsy demonstrated small or absent type 2A muscle fibers and reduced or absent expression of the corresponding MyHC IIa transcript and protein. We conclude that mild muscle weakness and ophthalmoplegia in combination with muscle biopsy demonstrating small or absent type 2A muscle fibers are the hallmark of recessive myopathy associated with MYH2 mutations.

Perivascular drainage of amyloid-beta peptides from the brain and its failure in cerebral amyloid angiopathy and Alzheimer's disease.

Alzheimer's disease is the commonest dementia. One major characteristic of its pathology is accumulation of amyloid-beta (Abeta) as insoluble deposits in brain parenchyma and in blood vessel walls [cerebral amyloid angiopathy (CAA)]. The distribution of Abeta deposits in the basement membranes of cerebral capillaries and arteries corresponds to the perivascular drainage pathways by which interstitial fluid (ISF) and solutes are eliminated from the brain--effectively the lymphatic drainage of the brain. Theoretical models suggest that vessel pulsations supply the motive force for perivascular drainage of ISF and solutes. As arteries stiffen with age, the amplitude of pulsations is reduced and insoluble Abeta is deposited in ISF drainage pathways as CAA, thus, further impeding the drainage of soluble Abeta. Failure of perivascular drainage of Abeta and deposition of Abeta in the walls of arteries has two major consequences: (i) intracerebral hemorrhage associated with rupture of Abeta-laden arteries in CAA; and (ii) Alzheimer's disease in which failure of elimination of ISF, Abeta and other soluble metabolites from the brain alters homeostasis and the neuronal environment resulting in cognitive decline and dementia. Therapeutic strategies that improve elimination of Abeta and other soluble metabolites from the brain may prevent cognitive decline in Alzheimer's disease.

Abeta-related angiitis: primary angiitis of the central nervous system associated with cerebral amyloid angiopathy.

Idiopathic or primary angiitis of the CNS (PACNS) and cerebral amyloid angiopathy (CAA) are unusual vasculopathies generally regarded as unrelated disorders. A few case reports have, however, described granulomatous angiitis in patients with sporadic, amyloid beta peptide (Abeta)-related CAA. Here we describe the clinical, neuroradiological and neuropathological features of nine patients with Abeta-related angiitis (ABRA). Combining these with the individual case reports drawn from the literature has allowed us to define ABRA as a clinical entity and to compare its features with those of PACNS. The mean age of presentation of ABRA (67 years) is higher than that of PACNS but lower than that of sporadic non-inflammatory Abeta-related CAA. Alterations in mental status (59%), headaches (35%), seizures and focal neurological deficits (24%) are common. Hallucinations are a presenting manifestation in 12% of cases. Most patients have white matter hyperintensities on MRI but these are of similar appearance to those in PACNS. Cerebrospinal fluid usually shows modest elevation of protein and pleocytosis. Neuropathology reveals angiodestructive inflammation, often granulomatous, and meningeal lymphocytosis. Abeta is consistently present in abundance in affected blood vessels but usually scanty within the parenchyma of the cerebral cortex. However, the cortex includes numerous activated microglia, occasionally in a plaque-like distribution and containing cytoplasmic Abeta. The cerebral white matter shows patchy gliosis and rarefaction, in some cases marked. Our findings (i) help to dissect one separate clinicopathological entity from what is likely to be a spectrum of primary angiitides of the CNS; (ii) have important therapeutic implications for one category of patients with amyloid-related vasculopathy; and (iii) may provide valuable insights into the development of amyloid-associated inflammation, of relevance not only to ABRA but also to Abeta-immunization-related encephalitis and to Alzheimer's disease.

Cerebrovascular disease is a major factor in the failure of elimination of Abeta from the aging human brain: implications for therapy of Alzheimer's disease.

Alzheimer's disease (AD) is characterized by the intracellular deposition of ubiquitinated tau and by the extracellular accumulation of soluble, insoluble, and fibrillary Abeta. Previous studies suggest that Abeta is normally eliminated from the brain along perivascular pathways that may become blocked in the aging brain, resulting in cerebral amyloid angiopathy. As age is a major risk factor for AD and for cerebrovascular disease (CVD), we test the hypothesis that CVD inhibits the elimination of Abeta from the aging human brain. Sections from 100 aged and AD brains were stained for Abeta by immunohistochemistry and by reticulin and Masson trichrome techniques. Early deposition of Abeta in brain parenchyma was related to individual arterial territories in the cortex. In areas of more extensive accumulation of Abeta, there was an inverse relationship between capillary amyloid angiopathy and plaques of Abeta. Thus, arterial territories with extensive capillary amyloid angiopathy were devoid of Abeta plaques, whereas in areas with abundant diffuse plaques there was no capillary amyloid angiopathy. Serial sections showed that cortical arteries feeding capillary beds with Abeta angiopathy were occluded by thrombus. We conclude that CVD inhibits the elimination of Abeta along capillary walls and changes the distribution of Abeta in the cerebral cortex. Loss of pulsations in thrombosed or arteriosclerotic arteries may thus abolish the motive force necessary for the drainage of Abeta and inhibit the elimination of Abeta. Therapies to increase elimination of Abeta in AD need to consider the effects of CVD on the elimination of Abeta from the aging human brain.