Recessive spastic paraparesis associated with complex I deficiency due to MTHFR mutations

Variable neurological phenotypes of homocystinuria caused by biallelic methylenetetrahydrofolate reductase variants

Inherited methylenetetrahydrofolate reductase (MTHFR) deficiency is associated with a wide spectrum of disorders including homocystinuria. This study aims to describe the neurological phenotypes and molecular profiles of patients with homocystinuria caused by biallelic variants in MTHFR. We report six subjects with MTHFR deficiency who presented with variable neurological phenotypes which could be viewed as a continuous spectrum. Fatal infantile encephalopathy was observed in one family, whereas another patient presented at 27 years with acute leukoencephalopathy and recovered within 3 months. Intermediate forms presenting as complicated hereditary spastic paraparesis of variable severity were observed in four subjects. Clinical and molecular information of the 207 cases reported in literature were also retrieved and analyzed. We categorized all subjects into three categories - severe, intermediate and mild forms according to the clinical presentation. In addition, a total of 286 disease-causing variations reported to date were analyzed. These included seven disease-causing variants reported in this study of which one is novel. Some genotype-phenotype correlation could be seen which corroborated with previous observations. However, inter- and intrafamilial variability was also noted. Treatment with betaine, B12 and folic acid was started in four subjects with variable outcomes.

Clinical and molecular characterization of adult patients with late-onset MTHFR deficiency

5,10-Methylenetetrahydrofolate reductase (MTHFR) deficiency usually presents as a severe neonatal disease. This study aimed to characterize natural history, biological and molecular data, and response to treatment of patients with late-onset MTHFR deficiency. The patients were identified through the European Network and Registry for Homocystinuria and Methylation Defects and the Adult group of the French Society for Inherited Metabolic Diseases; data were retrospectively colleted. To identify juvenile to adult-onset forms of the disease, we included patients with a diagnosis established after the age of 10 years. We included 14 patients (median age at diagnosis: 32 years; range: 11-54). At onset (median age: 20 years; range 9-38), they presented with walking difficulties (n = 8), cognitive decline (n = 3) and/or seizures (n = 3), sometimes associated with mild mental retardation (n = 6). During the disease course, symptoms were almost exclusively neurological with cognitive dysfunction (93%), gait disorders (86%), epilepsy (71%), psychiatric symptoms (57%), polyneuropathy (43%), and visual deficit (43%). Mean diagnostic delay was 14 years. Vascular events were observed in 28% and obesity in 36% of the patients. One patient remained asymptomatic at the age of 55 years. Upon treatment, median total homocysteine decreased (from 183 μmol/L, range 69-266, to 90 μmol/L, range 20-142) and symptoms improved (n = 9) or stabilized (n = 4). Missense pathogenic variants in the C-terminal regulatory domain of the protein were over-represented compared to early-onset cases. Residual MTHFR enzymatic activity in skin fibroblasts (n = 4) was rather high (17%-58%). This series of patients with late-onset MTHFR deficiency underlines the still unmet need of a prompt diagnosis of this treatable disease.

Rapidly Progressive Spastic Paraplegia Due to Hyperhomocysteinemia in Child with MTHFR Gene Mutation and Mitochondrial Complex I Deficiency: A Rare Association

MTHFR enzyme deficiency is an autosomal-recessive inborn error of folate metabolism. The deficiency cause defect in the remethylation of homocysteine to methionine leading to increased blood levels of homocysteine. Hyperhomocysteinemia in infants cause seizures, hypotonia, apnoea, microcephaly, progressing to coma and death if untreated whereas in childhood onset it causes developmental delay, seizures, psychiatric disturbances, spastic gait, and ataxia. We report a 10-year-old girl with rapidly progressive spastic paraplegia requiring wheelchair ambulation within 3 months of symptom onset with behavioral disturbances. Plasma homocysteine and plasma lactate were high with normal vitamin B12 levels. Clinical exome sequencing showed homozygous missense mutation in MTHFR gene which was likely pathogenic variant. Respiratory chain complex assay from muscle sample showed reduced complex 1 deficiency (<20%).

Clinical, biochemical, radiological, and genetic profile of patients with homocysteine remethylation pathway defect and spastic paraplegia

Objectives:

The objective of this study is to describe the clinical, biochemical, radiological, and genetic profile of patients presenting with progressive spastic paraparesis due to homocysteine remethylation pathway defect.

Methods:

This was a retrospective study conducted by reviewing the medical records of patients with serum homocysteine levels >50 μmol/L between January 2015 and January 2019 at our hospital. We included patients presenting with progressive spastic paraparesis, having serum homocysteine >50 μmol/L with low or normal blood methionine suggesting disorders of homocysteine remethylation. Demographic details, clinical manifestations, biochemical abnormalities, neuroimaging findings, and genetic profile were analyzed.

Results:

A total of seven patients (M: F = 5:2) fulfilled the study eligibility criteria. The mean age at onset of the disease was 13.4 ± 2.4 years (range: 9–17 years). Spastic paraparesis was the presenting manifestation in 4/7 (57.1%) patients. Other manifestations included cognitive decline, poor scholastic performance, behavioral disturbances, seizures, and spastic bladder. Severe hyperhomocysteinemia (>100 μmol/L) was noted in 6/7 (85.7%) patients with median levels of serum homocysteine being 185.7 μmol/L (range: 85.78–338.5 μmol/L). Neuroimaging showed parieto-occipital predominant leukoencephalopathy in 5/7 (71.4%) and diffuse cerebral atrophy in 1/7 (14.2%). Genetic analysis in three patients revealed pathogenic missense variants c.459C >G (p.Ile153Met), c.973C >T (p.Arg325Cys), and c.1031G >T (p.Arg344Met) in MTHFR gene. All the patients received vitamin B12 (injection and oral), folic acid, and pyridoxine and two patients received betaine. At the last follow-up of a median duration of 12 months, there was a good clinical and biochemical response with reduction in the median value of serum homocysteine by 77.5 μmol/L.

Conclusion:

Evaluation of serum homocysteine and blood methionine in adolescents presenting with progressive spastic paraparesis gives clue to a treatable homocysteine remethylation disorders.

Adult-onset methylenetetrahydrofolate reductase deficiency

Severe hyperhomocysteinemia (>100 µmol/L) is often associated with inborn errors of homocysteine metabolism. It manifests typically in neonatal period with developmental delay, hypotonia, feeding problems or failure to thrive. Adult-onset forms are rare and include less severe manifestations. Early diagnosis is crucial because effective treatment is available. A 23-year-old man presented with a 3-week history of speech and gait impairment, and numbness in lower limbs. Neurological examination revealed dysarthria, decreased vibratory sensation in both legs and appendicular and gait ataxia. Brain MRI revealed T2-hyperintense symmetric white matter lesions and cortical atrophy. He had folate and vitamin B₁₂ deficiency, a markedly elevated serum homocysteine and low methionine. Despite vitamin supplementation homocysteine levels remained elevated. Molecular studies of 5,10-methylenetetrahydrofolate reductase (MTHFR) gene revealed a new pathogenic mutation (c.1003C>T (p.Arg335Cys)) and a polymorphism (C677T (p.Ala222Val)) associated with hyperhomocysteinemia, both in homozygosity. The patient started betaine with clinical and biochemical improvement.

Mutations in MTHFR and POLG impaired activity of the mitochondrial respiratory chain in 46-year-old twins with spastic paraparesis

Hereditary spastic paraplegias (HSPs) are characterized by lower extremity spasticity and weakness. HSP is often caused by mutations in SPG genes, but it may also be produced by inborn errors of metabolism. We performed next-generation sequencing of 4813 genes in one adult twin pair with HSP and severe muscular weakness occurring at the same age. We found two pathogenic compound heterozygous variants in MTHFR, including a variant not referenced in international databases, c.197C>T (p.Pro66Leu) and a known variant, c.470G>A (p.Arg157Gln), and two heterozygous pathogenic variants in POLG, c.1760C>T (p.Pro587Leu) and c.752C>T (p.Thr251Ile). MTHFR and POLG mutations were consistent with the severe muscle weakness and the metabolic changes, including hyperhomocysteinemia and decreased activity of both N(5,10)methylenetetrahydrofolate reductase (MTHFR) and complexes I and II of the mitochondrial respiratory chain. These data suggest the potential role of MTHFR and POLG mutations through consequences on mitochondrial dysfunction in the occurrence of spastic paraparesis phenotype with combined metabolic, muscular, and neurological components.

Clinical pattern, mutations and in vitro residual activity in 33 patients with severe 5, 10 methylenetetrahydrofolate reductase (MTHFR) deficiency

BACKGROUND

Severe methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare inborn defect disturbing the remethylation of homocysteine to methionine (<200 reported cases). This retrospective study evaluates clinical, biochemical genetic and in vitro enzymatic data in a cohort of 33 patients.

METHODS

Clinical, biochemical and treatment data was obtained from physicians by using a questionnaire. MTHFR activity was measured in primary fibroblasts; genomic DNA was extracted from cultured fibroblasts.

RESULTS

Thirty-three patients (mean age at follow-up 11.4 years; four deceased; median age at first presentation 5 weeks; 17 females) were included. Patients with very low (<1.5%) mean control values of enzyme activity (n = 14) presented earlier and with a pattern of feeding problems, encephalopathy, muscular hypotonia, neurocognitive impairment, apnoea, hydrocephalus, microcephaly and epilepsy. Patients with higher (>1.7-34.8%) residual enzyme activity had mainly psychiatric symptoms, mental retardation, myelopathy, ataxia and spasticity. Treatment with various combinations of betaine, methionine, folate and cobalamin improved the biochemical and clinical phenotype. During the disease course, patients with very low enzyme activity showed a progression of feeding problems, neurological symptoms, mental retardation, and psychiatric disease while in patients with higher residual enzyme activity, myelopathy, ataxia and spasticity increased. All other symptoms remained stable or improved in both groups upon treatment as did brain imaging in some cases. No clear genotype-phenotype correlation was obvious.

DISCUSSION

MTHFR deficiency is a severe disease primarily affecting the central nervous system. Age at presentation and clinical pattern are correlated with residual enzyme activity. Treatment alleviates biochemical abnormalities and clinical symptoms partially.