Molecular characterization of folate receptor 1 mutations delineates cerebral folate transport deficiency.

Cerebral folate transport deficiency is an inherited brain-specific folate transport defect that is caused by mutations in the folate receptor 1 gene coding for folate receptor alpha (FRα). This genetic defect gives rise to a progressive neurological disorder with late infantile onset. We screened 72 children with low 5-methyltetrahydrofolate concentrations in the cerebrospinal fluid and neurological symptoms that developed after infancy. We identified nucleotide alterations in the folate receptor 1 gene in 10 individuals who shared developmental regression, ataxia, profound cerebral hypomyelination and cerebellar atrophy. We found four novel pathogenic alleles, one splice mutation and three missense mutations. Heterologous expression of the missense mutations, including previously described mutants, revealed minor decrease in protein expression but loss of cell surface localization, mistargeting to intracellular compartments and thus absence of cellular binding of folic acid. These results explain the functional loss of folate receptor alpha for all detected folate receptor 1 mutations. Three individuals presenting a milder clinical phenotype revealed very similar biochemical and brain imaging data but partially shared pathogenic alleles with more severely affected patients. Thus, our studies suggest that different clinical severities do not necessarily correlate with residual function of folate receptor alpha mutants and indicate that additional factors contribute to the clinical phenotype in cerebral folate transport deficiency.

POLG1 manifestations in childhood.

OBJECTIVE: Mitochondrial DNA polymerase γ (POLG1) mutations in children often manifest as Alpers syndrome, whereas in adults, a common manifestation is mitochondrial recessive ataxia syndrome (MIRAS) with severe epilepsy. Because some patients with MIRAS have presented with ataxia or epilepsy already in childhood, we searched for POLG1 mutations in neurologic manifestations in childhood. METHODS: We investigated POLG1 in 136 children, all clinically suspected to have mitochondrial disease, with one or more of the following: ataxia, axonal neuropathy, severe epilepsy without known epilepsy syndrome, epileptic encephalopathy, encephalohepatopathy, or neuropathologically verified Alpers syndrome. RESULTS: Seven patients had POLG1 mutations, and all of them had severe encephalopathy with intractable epilepsy. Four patients had died after exposure to sodium valproate. Brain MRI showed parieto-occipital or thalamic hyperintense lesions, white matter abnormality, and atrophy. Muscle histology and mitochondrial biochemistry results were normal in all. CONCLUSIONS: POLG1 analysis should belong to the first-line DNA diagnostic tests for children with an encephalitis-like presentation evolving into epileptic encephalopathy with liver involvement (Alpers syndrome), even if brain MRI and morphology, respiratory chain activities, and the amount of mitochondrial DNA in the skeletal muscle are normal. POLG1 analysis should precede valproate therapy in pediatric patients with a typical phenotype. However, POLG1 is not a common cause of isolated epilepsy or ataxia in childhood.

DARS2 mutations in mitochondrial leucoencephalopathy and multiple sclerosis.

BACKGROUND: Leucoencephalopathy with brain stem and spinal cord involvement and high brain lactate (LBSL) was first defined by characteristic magnetic resonance imaging and spectroscopic findings. The clinical features include childhood or juvenile onset slowly progressive ataxia, spasticity, and dorsal column dysfunction, occasionally accompanied by learning difficulties. Mutations in DARS2, encoding mitochondrial aspartyl-tRNA synthetase, were recently shown to cause LBSL. The signs and symptoms show some overlap with the most common leucoencephalopathy of young adults, multiple sclerosis (MS). OBJECTIVE: To clarify the molecular background of LBSL patients in Finland, and to look for DARS2 mutations in a group of MS patients. METHODS: Clinical evaluation of LBSL patients, DARS2 sequencing and haplotype analysis, and carrier frequency determination in Finland. RESULTS: All eight LBSL patients were compound heterozygotes for DARS2 mutations: all carried R76SfsX5 change, seven had M134_K165del, and one had C152F change. Axonal neuropathy was found in five of the eight patients. The carrier frequencies of the R76SfsX5 and M134_K165del mutations were 1:95 and 1:380, respectively. All patients shared common European haplotypes, suggestive of common European LBSL ancestors. No enrichment of the two common DARS2 mutations was found in 321 MS patients. CONCLUSION: All LBSL patients were compound heterozygotes, which suggests that DARS2 mutation homozygosity may be lethal or manifest as a different phenotype. The authors show here that despite identical mutations the clinical picture was quite variable in the patients. Axonal neuropathy was an important feature of LBSL. DARS2 mutations cause childhood-to-adolescence onset leucoencephalopathy, but they do not seem to be associated with MS.

Hypomyelination with atrophy of the basal ganglia and cerebellum: follow-up and pathology.

BACKGROUND AND OBJECTIVE: Hypomyelination with atrophy of the basal ganglia and cerebellum is a recently defined disorder. Only a few patients have been described. We report on 11 additional patients and new MRI findings and provide histopathologic confirmation of the MRI interpretation. METHODS: We reviewed the patients' clinical history and present findings. We scored the MRI abnormalities. The histopathology of one patient was re-examined. RESULTS: The patients' early psychomotor development was normal or delayed, followed by increasing extrapyramidal movement abnormalities, ataxia, and spasticity. Mental capacities were variably affected. MRI showed hypomyelination with, on follow-up, evidence of further myelin loss and variable white matter atrophy. The putamen was small or, more often, absent; the head of the caudate nucleus was decreased in size. In contrast, the thalamus and globus pallidus remained normal. Cerebellar atrophy was invariably present. Histopathology confirmed the myelin deficiency, probably related to both lack of deposition and low-grade further loss. The degeneration of putamen was subtotal. The cerebellar cortex was affected, particularly the granular layer. CONCLUSION: Hypomyelination with atrophy of the basal ganglia and cerebellum is a syndrome diagnosed by distinctive MRI findings. Histopathology confirms hypomyelination, low-grade further myelin loss, subtotal degeneration of the putamen, and cerebellar cortical atrophy. All known patients are sporadic, and the mode of inheritance is unclear.

Mapping susceptibility gene locus for IgA deficiency at del(18)(q22.3-q23); report of familial cryptic chromosome t(18q; 10p) translocations.

This study presents a clinical report of the Finnish chromosome t(18q; 10p) translocation family with an overview of eight other selected immunoglobulin A (IgA)-deficient 18q deletion (18q-) patients from seven published articles. The family members show features common to 18q- syndrome such as mental retardation, multiple facial dysmorphism, foot/hand deformities, abnormal myelination of brain white matter, and a spectrum of immunological/infectious disorders including IgA deficiency (IgAD). Genotype-phenotype correlation study of the unbalanced t(18q-; 10p+) translocation family members and other 18q- syndrome reports led to definition of a potential susceptibility gene locus for IgAD at distal region of 18q22.3-q23 between markers D18S812-18qter. The haplo-insufficiency of the 18q22.3-q23 gene region is suggested to be a cause of the IgAD phenotype in 18q- individuals. This 7 Mb IgAD critical region shows significant association with susceptibility region for celiac disease that is frequently connected to IgAD.

Cerebroretinal microangiopathy with calcifications and cysts.

BACKGROUND: Extensive cerebral calcifications and leukoencephalopathy have been reported in two rare disorders Coats plus and leukoencephalopathy with calcifications and cysts. In the latter, a progressive formation of parenchymal brain cysts is a special feature, whereas Coats plus is characterized by intrauterine growth retardation, bilateral retinal telangiectasias and exudations (Coats disease), sparse hair, and dysplastic nails without cyst formation. METHODS: We identified 13 patients, including two pairs of siblings, with extensive cerebral calcifications and leukoencephalopathy. We reviewed clinical, ophthalmologic, radiologic and neuropathologic data of seven deceased patients and studied five patients prospectively. RESULTS: 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 and, in five patients, cerebral cysts. Eleven patients had retinal telangiectasias or angiomas. Additional features were skeletal and hematologic abnormalities, intestinal bleeding, and poor growth. Neuropathologic examination showed extensive calcinosis and abnormal small vessels with thickened, hyalinized wall and reduced lumen. CONCLUSIONS: Our data suggest that Coats plus syndrome and leukoencephalopathy with calcifications and cysts belong to the same spectrum. The primary abnormality seems to be an obliterative cerebral angiopathy involving small vessels, leading to dystrophic calcifications via slow necrosis and finally to formation of cysts and secondary white matter abnormalities.

Five new cases of a recently described leukoencephalopathy with high brain lactate.

BACKGROUND: A new leukoencephalopathy with brainstem and spinal cord involvement and high brain lactate was recently defined. The authors describe five new patients with this entity. METHODS: Brain MRI was performed in all patients and spinal MRI and proton magnetic resonance spectroscopy (1H-MRS) in four patients. Laboratory examinations ruled out classic leukodystrophies. RESULTS: MRI showed signal abnormalities in the periventricular and deep white matter, in the pyramidal tracts, mesencephalic trigeminal tracts, in the cerebellar connections, and in dorsal columns of the spinal cord. MRS showed decreased N-acetylaspartate and increased lactate in the white matter of all patients. In one patient choline-containing compounds were elevated. A slowly progressive sensory ataxia and tremor manifested at the age of 3 to 16 years and distal spasticity in adolescence. One 13-year-old patient was asymptomatic. CONCLUSIONS: A slowly progressive sensory ataxia is a typical feature in this new leukodystrophy. MRS favors a primary axonal degeneration.

A case of Salla disease with involvement of the cerebellar white matter.

Salla disease (SD) is a lysosomal disorder manifesting in infancy with hypotonia, nystagmus, ataxia and retarded motor development. MRI typically shows hypomyelination confined to the cerebral white matter. We describe a patient with two MRI studies in addition to repeated urine examinations. This case was problematic because the first urine examination did not show the elevation of free sialic acid typical of SD and MRI was also atypical, with abnormal signal intensity in cerebellar white matter. We recommend repeated urinary examinations and a search for SLC17A5 mutations in patients with cerebral signal intensity abnormalities typical of SD and emphasise that cerebellar white-matter involvement on MRI does not exclude the diagnosis.