Cerebroretinal Microangiopathy With Calcifications And Cysts 1

A number sign (#) is used with this entry because of evidence that cerebroretinal microangiopathy with calcifications and cysts-1 (CRMCC1), also known as Coats plus syndrome, is caused by compound heterozygous mutation in the CTC1 gene (613129) on chromosome 17p13.

Description

Cerebroretinal microangiopathy with calcifications and cysts (CRMCC), also known as Coats plus syndrome, is an autosomal recessive pleomorphic disorder characterized primarily by intracranial calcifications, leukodystrophy, and brain cysts, resulting in spasticity, ataxia, dystonia, seizures, and cognitive decline. Patients also have retinal telangiectasia and exudates (Coats disease) as well as extraneurologic manifestations, including osteopenia with poor bone healing and a high risk of gastrointestinal bleeding and portal hypertension caused by vasculature ectasias in the stomach, small intestine, and liver. Some individuals also have hair, skin, and nail changes, as well as anemia and thrombocytopenia (summary by Anderson et al., 2012 and Polvi et al., 2012).

Leukoencephalopathy, brain calcifications, and cysts (LCC), also known as Labrune syndrome (614561), has similar central nervous system features as CRMCC in the absence of extraneurologic or systemic manifestations. Although Coats plus syndrome and Labrune syndrome were initially thought to be manifestations of the same disorder, namely CRMCC, molecular evidence has excluded mutations in the CTC1 gene in patients with Labrune syndrome, suggesting that the 2 disorders are not allelic (Anderson et al., 2012; Polvi et al., 2012).

Some features of CRMCC resemble those observed in dyskeratosis congenita (see, e.g., 127550), which is a clinically and genetically heterogeneous telomere-related genetic disorder.

Genetic Heterogeneity of Cerebroretinal Microangiopathy With Calcifications And Cysts

See also CRMCC2 (617341), caused by mutation in the STN1 gene (613128) on chromosome 10q24.

Clinical Features

Tolmie et al. (1988) reported 2 sisters of Scottish descent with bilateral retinal telangiectasia, also referred to as Coats reaction of the retina (300216), intracranial calcification, sparse hair, and dysplastic nails. The older sister had exudative vasculopathy of the retina treated with enucleation of 1 eye and laser in the other. IQ was normal. Her younger sister presented at age 7 months with febrile seizures and was later found to have strabismus and retinal exudates. She had calcifications in the cerebrum and cerebellum, as well as ataxia by age 3.5 years. The authors postulated autosomal recessive inheritance. In a follow-up report of the family reported by Tolmie et al. (1988), Crow et al. (2004) described skeletal defects, including abnormal bone marrow, osteopenia, and sclerosis with a tendency to fracture. The sisters also had a mixed cerebellar and extrapyramidal movement disorder, occasional seizures, leukodystrophy, and postnatal growth failure. The younger sister had retinal angiomas and recurrent vitreous hemorrhages, resulting in blindness by age 7 years. Intellect was normal, but the younger sister had psychologic difficulties. Briggs et al. (2008) reported follow-up of the older sister reported by Tolmie et al. (1988). She gave birth to a female without significant maternal health issues. The infant has problems related to prematurity, but no signs of Coats disease or intracranial complications at age 3 years. At age 23 years, the mother developed rectal bleeding and was found to have large telangiectatic mucosal blood vessels and esophageal varices with chronic liver disease and portal hypertension.

Crow et al. (2004) reported 2 unrelated patients with a similar phenotype, including intracranial calcifications, bilateral Coats disease, poor growth, sparse hair, dysplastic nails, leukodystrophy, and increased fractures. The girl had low-normal intelligence at age 11 years. The boy showed Coats disease, mild spastic hemiparesis at age 5 years, and progressive leukodystrophy. He later developed seizures and was found to have sclerotic and lytic bone changes.

Nagae-Poetscher et al. (2004) reported 3 unrelated patients with leukoencephalopathy and cerebral calcifications and cysts. One of the female patients was born to consanguineous parents, and the male patient had Coats disease. Clinical features included infantile or early childhood onset of dystonia, spasticity, ataxia, and hemiplegia. Biopsy of a cerebral cyst from 1 patient showed Rosenthal fibers and macrophages with iron deposits.

Linnankivi et al. (2006) reported 13 patients, including 2 sib pairs, with extensive cerebral calcifications and leukoencephalopathy. Eleven patients were small for gestational age; the other symptoms emerged from infancy to adolescence. All patients had neurologic symptoms including seizures, spasticity, dystonia, ataxia, and cognitive decline. Progressive intracerebral calcifications involved deep gray nuclei, brainstem, cerebral and cerebellar white matter, and dentate nuclei and were accompanied by diffuse white matter signal changes. Eleven patients had retinal telangiectases or angiomas, and 5 had cerebral cysts. Additional features included skeletal and hematologic abnormalities, intestinal bleeding, and poor growth. Six patients had sparse hair, but none had nail abnormalities. Neuropathologic examination showed extensive calcinosis and abnormal small vessels with thickened, hyalinized wall and reduced lumen. Linnankivi et al. (2006) concluded that Coats plus syndrome and leukoencephalopathy with calcifications and cysts (LCC) belong to the same spectrum. The authors postulated that the primary abnormality is an obliterative cerebral angiopathy involving small vessels, leading to dystrophic calcifications, slow necrosis, cyst formation, and secondary white matter abnormalities.

Briggs et al. (2008) reported 8 patients with a progressive disorder that they referred to as cerebroretinal microangiopathy with calcifications and cysts (CRMCC). Six patients had features consistent with Coats plus syndrome. Patient 7 had similar features with intrauterine growth retardation, intracranial calcification, white matter changes, and ectodermal involvement, although there were no retinal abnormalities at the age of 3 years. Patients 8 and 9 had intracerebral cysts. One patient had both an exudative retinopathy and cystic masses at the level of the midbrain and upper pons identified at autopsy. These overlapping features had been reported by Nagae-Poetscher et al. (2004) and Linnankivi et al. (2006), suggesting that Coats plus and LCC are manifestations of the same disease spectrum. Briggs et al. (2008) noted that key clinical features involved include pre- and postnatal growth retardation, bilateral retinal telangiectasia and retinal exudates, intracranial calcification, leukodystrophy, occasional parenchymal brain cysts, osteopenia and a tendency to fractures, bone marrow suppression, and gastrointestinal bleeding with cirrhosis. Less frequent features included sparse graying hair and dystrophic nails. Most patients showed progression of their neurologic disease with spasticity, dystonia, ataxia, and cognitive decline. The clinical phenotype of CRMCC is thus wide and variable, and affected individuals may present to multiple specialists. Autosomal recessive inheritance appeared most likely.

Toiviainen-Salo et al. (2011) specifically addressed the skeletal phenotype of 9 unrelated Finnish patients with CRMCC, including 8 who had been reported by Linnankivi et al. (2006) and 1 novel patient. The patients ranged in age from 4 to 31 years, and 6 had died between ages 6 and 31. Radiographic analysis showed impaired longitudinal growth pre- and postnatally, generalized osteopenia or early-onset low turnover osteoporosis with fragility fractures, and metaphyseal abnormalities that led to limb deformities such as short femoral neck or genua valga. Three patients showed low bone mineral density on scan, and bone biopsies in a fourth patient with pathologic fractures and impaired fracture healing showed low-turnover osteoporosis with reduced osteoclast and osteoblast activity. Direct sequencing of the LRP5 gene (603506) excluded pathogenic mutations in coding exons and exon-intron boundaries.

Anderson et al. (2012) reported 11 families with Coats plus syndrome, defined as intracranial calcifications, leukoencephalopathy, and early-onset retinal changes, associated with extraneurologic manifestations including early-onset bone fractures, gastrointestinal ectasia, and variable hair, nail, and skin changes, and/or anemia. Five of the families had previously been reported by Briggs et al. (2008), and 1 by Crow et al. (2004).

Clinical Variability

Keller et al. (2012) reported an 18-year-old girl who presented at age 15 years with classic features of dyskeratosis congenita (see, e.g., 127550), including bone marrow failure, abnormalities in skin pigmentation, nail dysplasia, and graying hair. She also had short stature, osteopenia, decreased pulmonary function, and blurry vision associated with sheathed vessels and microaneurysm formation in the retina. Brain MRI showed calcifications in the right thalamus, and telomeres were shortened significantly. Neurologic function was normal. Patient fibroblasts showed a defect in outgrowth as well as rapid senescence compared to controls. Genetic analysis excluded mutations in known DKC-associated genes, and identified compound heterozygous mutations in the CTC1 gene (613129.0001 and 613129.0012). Keller et al. (2012) noted that both CTC1 mutations had been reported in patients with Coats plus syndrome, suggesting that Coats plus syndrome and DKC show phenotypic and genetic overlap, consistent with a telomere-related disease.

Molecular Genetics

In affected individuals from 10 families with Coats plus syndrome, Anderson et al. (2012) identified 14 different mutations in the CTC1 gene (see, e.g., 613129.0001-613129.0005; 613129.0012-613129.0013). The first mutations were found by exome sequencing of 2 sibs. All patients were compound heterozygous for 2 mutations. Three patients were found to have shortened telomere lengths in white blood cells, and heterozygous family members had telomere lengths at the lower range of normal. Cell lines derived from 2 patients showed an increase in spontaneous H2AX histone (601772)-positive cells, indicating an ongoing DNA damage response. Noting the role of CTC1 in DNA replication, Anderson et al. (2012) concluded that mutations in the CTC1 gene may disrupt DNA metabolism and telomere integrity. One family did not have a CTC1 mutation, suggesting genetic heterogeneity. In addition, sequencing excluded mutations in the CTC1 gene in 21 probands with Labrune syndrome, defined as intracranial calcifications and leukoencephalopathy without extraneurologic features, suggesting that these 2 disorders may not be allelic, even though they show phenotypic overlap.

Polvi et al. (2012) identified compound heterozygous mutations in the CTC1 gene (see, e.g., 613129.0006-613129.0011) in 13 of 15 patients with cerebroretinal microangiopathy with calcifications and cysts. The mutations were found by whole-exome sequencing in 4 apparently unrelated Finnish patients, followed by Sanger sequencing of the CTC1 gene in 11 additional patients from 10 families. Ten of the 15 patients had previously been reported (see, e.g., Linnankivi et al., 2006 and Briggs et al., 2008). A total of 11 mutations were found, 2 of which were recurrent (V665G, 613129.0006 and 2831delC, 613129.0007). Ten of the 12 families carried a missense mutation on 1 allele and a truncating mutation on the other allele. Only 1 patient carried 2 in-frame deletions, likely resulting in a protein product with altered functional properties; this patient had few extracranial manifestations. Since no patient carried 2 truncating mutations, it appeared likely that such a combination would be lethal in utero. CTC1 mutations were found in all patients with childhood onset of the disorder and with retinal involvement. Two of 3 patients with later onset and lack of clinical retinal anomalies did not carry CTC1 mutations; these 2 patients did not have systemic findings. There were no differences in telomere lengths in patients with CTC1 mutations compared to controls, suggesting that telomere integrity is not severely compromised in this disorder.

Pathogenesis

Gu and Chang (2013) performed biochemical characterization of human CTC1 mutations involved in Coats plus telomere disease. They found that all CTC1 frameshift mutations generated truncated or unstable protein products that could not form CTC1-STN1 (613128)-TEN1 (613130) (CST) complexes on telomeres, leading to progressive telomere shortening and formation of fused chromosomes. Missense mutations resulted in proteins that could form CST complexes, but their expression levels were often repressed by the frameshift mutants. CTC1 mutations promoted telomere dysfunction by decreasing the stability of STN1 and reducing the ability of STN1 to interact with DNA polymerase-alpha (POLA; see 312040). Gu and Chang (2013) proposed that failure of STN1 to interact with POLA would make inactivating STN1 mutations incompatible with survival.