Myopathy is a prominent feature in Marinesco-Sjögren syndrome: A muscle computed tomography study

Role of the HSP70 Co-Chaperone SIL1 in Health and Disease

Cell surface and secreted proteins provide essential functions for multicellular life. They enter the endoplasmic reticulum (ER) lumen co-translationally, where they mature and fold into their complex three-dimensional structures. The ER is populated with a host of molecular chaperones, associated co-factors, and enzymes that assist and stabilize folded states. Together, they ensure that nascent proteins mature properly or, if this process fails, target them for degradation. BiP, the ER HSP70 chaperone, interacts with unfolded client proteins in a nucleotide-dependent manner, which is tightly regulated by eight DnaJ-type proteins and two nucleotide exchange factors (NEFs), SIL1 and GRP170. Loss of SIL1′s function is the leading cause of Marinesco-Sjögren syndrome (MSS), an autosomal recessive, multisystem disorder. The development of animal models has provided insights into SIL1′s functions and MSS-associated pathologies. This review provides an in-depth update on the current understanding of the molecular mechanisms underlying SIL1′s NEF activity and its role in maintaining ER homeostasis and normal physiology. A precise understanding of the underlying molecular mechanisms associated with the loss of SIL1 may allow for the development of new pharmacological approaches to treat MSS.

Marinesco-Sjögren syndrome due to SIL1 mutations with a comment on the clinical phenotype

BACKGROUND

Marinesco-Sjögren syndrome is an autosomal recessive cerebellar ataxia, characterised by cerebellar ataxia, myopathy, cataracts and intellectual disability, due to mutations in the SIL1 gene.

METHODS

The clinical features and two novel SIL1 mutations of four Dutch patients with Marinesco-Sjögren syndrome are described and compared to the literature on genetically proven Marinesco-Sjögren patients.

RESULTS

The core phenotype of this syndrome appears homogeneous, but: [1] cataract can develop later than the motor and cognitive signs; [2] myopathy is an early feature that seems progressive during the course of the disease; [3] serum creatine kinase is normal or only mildly elevated; [4] peripheral neuropathy is absent; and [5] a variable degree of intellectual disability is present in most Marinesco-Sjögren patients.

CONCLUSIONS

Because the late appearance of some hallmarks and the uncertainty as to whether incomplete phenotypes occur, SIL1 mutation analysis is helpful early in the diagnostic work-up of children with suspected inherited ataxias.

The use of muscle biopsy in the diagnosis of undefined ataxia with cerebellar atrophy in children

Childhood cerebellar ataxias, and particularly congenital ataxias, are heterogeneous disorders and several remain undefined. We performed a muscle biopsy in patients with congenital ataxia and children with later onset undefined ataxia having neuroimaging evidence of cerebellar atrophy. Significant reduced levels of Coenzyme Q10 (COQ10) were found in the skeletal muscle of 9 out of 34 patients that were consecutively screened. A mutation in the ADCK3/Coq8 gene (R347X) was identified in a female patient with ataxia, seizures and markedly reduced COQ10 levels. In a 2.5-years-old male patient with non syndromic congenital ataxia and autophagic vacuoles in the muscle biopsy we identified a homozygous nonsense mutation R111X mutation in SIL1 gene, leading to early diagnosis of Marinesco-Sjogren syndrome. We think that muscle biopsy is a valuable procedure to improve diagnostic assesement in children with congenital ataxia or other undefined forms of later onset childhood ataxia associated to cerebellar atrophy at MRI.

A case of Marinesco-Sjögren syndrome: MRI observations of skeletal muscles, bone metabolism, and treatment with testosterone and risedronate

Marinesco-Sjögren syndrome (MSS) is a rare autosomal recessive disorder characterized by cerebellar ataxia, congenital cataracts, mental retardation, primary hypogonadism, skeletal abnormalities and myopathy, and patients with MSS are considered to be at risk of falls and bone fractures. We report a patient with MSS who received testosterone replacement therapy and risedronate administration. Muscle strength and the MRI features of the skeletal muscles were not changed, but low bone mass was improved by these treatments, and improvement has continued after risedronate treatment alone. This case suggests that treatment of MSS-related low bone mass using bisphosphonates is likely beneficial.