Janet A. Thomas

Methionine Adenosyltransferase I/III Deficiency: Novel Mutationsand Clinical Variations

Methionine adenosyltransferase (MAT) I/III deficiency, caused by mutations in the MAT1A gene, is characterized by persistent hypermethioninemia without elevated homocysteine or tyrosine. Clinical manifestations are variable and poorly understood, although a number of individuals with homozygous null mutations in MAT1A have neurological problems, including brain demyelination. We analyzed MAT1A in seven hypermethioninemic individuals, to provide insight into the relationship between genotype and phenotype. We identified six novel mutations and demonstrated that mutations resulting in high plasma methionines may signal clinical difficulties. Two patients-a compound heterozygote for truncating and severely inactivating missense mutations and a homozygote for an aberrant splicing MAT1A mutation-have plasma methionine in the 1,226-1,870 microM range (normal 5-35 microM) and manifest abnormalities of the brain gray matter or signs of brain demyelination. Another compound heterozygote for truncating and inactivating missense mutations has 770-1,240 microM plasma methionine and mild cognitive impairment. Four individuals carrying either two inactivating missense mutations or the single-allelic R264H mutation have 105-467 microM plasma methionine and are clinically unaffected. Our data underscore the necessity of further studies to firmly establish the relationship between genotypes in MAT I/III deficiency and clinical phenotypes, to elucidate the molecular bases of variability in manifestations of MAT1A mutations.

Genetic and clinical characterization of patients with an interstitial duplication 15q11-q13, emphasizing behavioral phenotype and response to treatment.

The clinical significance of an interstitial duplication of (15)(q11‐q13) remains unclear and controversial. The reported phenotypes vary widely and appear to be influenced by the parent of origin of the duplication. Aside from cases of dup(15) reported with autism, the behavioral phenotype of individuals with dup(15) has not been described. We present three families, two with intrachromosomal duplication (15)(q11‐q13) ascertained because of developmental delay in a relative. Two families show clear evidence of multigenerational maternal inheritance. The individuals discussed in this paper have minor anomalies and developmental delays. In addition, we describe a behavioral phenotype which often includes attention deficit hyperactivity disorder (ADHD) and autistic spectrum disorder. Responses to medications used to manage these behaviors are also described, including a positive response to methylphenidate and a poor response to fluoxetine. The duplication in each presenting individual, and available family members, was investigated utilizing cytogenetic and molecular techniques including high resolution cytogenetics, fluorescence in situ hybridization (FISH), DNA methylation studies, and quantitative fluorescence PCR. High resolution cytogenetic techniques alone missed some cases, demonstrating the need to confirm results with other methods.

Succinyl-CoA ligase deficiency: a mitochondrial hepatoencephalomyopathy

This patient presented on the first day of life with pronounced lactic acidosis with an elevated lactate/pyruvate ratio. Urine organic acids showed Krebs cycle metabolites and mildly elevated methylmalonate and methylcitrate. The acylcarnitine profile showed elevated propionylcarnitine and succinylcarnitine. Amino acids showed elevated glutamic acid, glutamine, proline, and alanine. From the age 2 of mo on, she had elevated transaminases and intermittent episodes of liver failure. Liver biopsy showed steatosis and a decrease of mitochondrial DNA to 50% of control. She had bilateral sensorineural hearing loss. Over the course of the first 2 y of life, she developed a progressively severe myopathy with pronounced muscle weakness eventually leading to respiratory failure, Leigh disease, and recurrent hepatic failure. The hepatic symptoms and the metabolic parameters temporarily improved on treatment with aspartate, but neither muscle symptoms nor brain lesions improved. Laboratory testing revealed a deficiency of succinyl-CoA ligase enzyme activity and protein in fibroblasts because of a novel homozygous mutation in the SUCLG1 gene: c.40A>T (p.M14L). Functional analysis suggests that this methionine is more likely to function as the translation initiator methionine, explaining the pathogenic nature of the mutation. Succinyl-CoA ligase deficiency due to an SUCLG1 mutation is a new cause for mitochondrial hepatoencephalomyopathy.

Late-onset combined homocystinuria and methylmalonic aciduria (cblC) and neuropsychiatric disturbance

We report on the case of a 36‐year‐old Hispanic woman with a spinal cord infarct, who was subsequently diagnosed with methylmalonic aciduria and homocystinuria, cblC type (cblC). Mutation analysis revealed c.271dupA and c.482G > A mutations in the MMACHC gene. The patient had a past medical history significant for joint hypermobility, arthritis, bilateral cataracts, unilateral hearing loss, anemia, frequent urinary tract infections, and mental illness. There was no significant past history of mental retardation, failure to thrive, or seizure disorder as reported in classic cases of cblC. Prior to the thrombotic incident, the patient experienced increased paresthesia in the lower extremities, myelopathy, and impaired gait. Given her previous psychiatric history, she was misdiagnosed with malingering until hemiplegia and incontinence became apparent. The authors would like to emphasize the recognition of a neuropsychiatric presentation in late onset cblC. Ten other reported late onset cases with similar presentations are also reviewed.

Clinical and molecular characterization of the first adult congenital disorder of glycosylation (CDG) type Ic patient

Congenital disorder of glycosylation (CDG) type Ic, the second largest subtype of CDG, is caused by mutations in human ALG6 (hALG6). This gene encodes the α1,3‐glucosyltransferase that catalyzes transfer of the first glucose residue to the lipid‐linked oligosaccharide precursor for N‐linked glycosylation. In this report, we describe the first adult patient diagnosed with CDG‐Ic, carrying two previously unknown mutations. The first is a three base deletion (897‐899delAAT) leading to the loss of I299, the second is an intronic mutation (IVS7 + 2T > G) that causes aberrant splicing. Wildtype hALG6, delivered by a lentiviral vector into patients fibroblasts, clearly improves the biochemical phenotype, which confirms that the mutations are disease‐causing. Striking clinical findings include limb deficiencies in the fingers, resembling brachydactyly type B, a deep vein thrombosis, pseudotumor cerebri, and endocrine disturbances with pronounced hyperandrogenism and virilization. However, even in adulthood, this patient shows normal magnetic resonance imaging of the brain.

The mitochondrial 13513G>A mutation is associated with Leigh disease phenotypes independent of complex I deficiency in muscle

The mitochondrial 13513G>A (D393N) mutation in the ND5 subunit of the respiratory chain complex I was initially described in association with MELAS syndrome. Recent observations have linked this mutation to Leigh disease. We screened for the 13513G>A mutation in a cohort of 265 patients with Leigh and Leigh-like disease. The mutation was found in a total of 5 patients. An additional patient who had clinical presentation consistent with a Leigh-like phenotype but with a normal brain MRI was added to the cohort. None of an additional 88 patients meeting MELAS disease criteria, nor 56 patients with respiratory chain deficiency screened for the 13513G>A were found positive for the mutation. The most frequent clinical manifestations in our patients were hypotonia, ocular and cerebellar involvement. Low mutation heteroplasmy in the range of 20-40% was observed in all 6 patients. This observation is consistent with the previously reported low heteroplasmy of this mutation in some patients with the 13513G>A mutation and complex I deficiency. However, normal complex I activity was observed in two patients in our cohort. As most patients with Leigh-like disease and the 13513G>A mutation have been described with complex I deficiency, this report adds to the previously reported subset of patients with normal respiratory complex function. We conclude that in any patient with Leigh or Leigh-like disease, testing for the 13513G>A mutation is clinically relevant and low mutant loads in blood or muscle may be considered pathogenic, in the presence of normal respiratory chain enzyme activities.

Constitutive induction of pro-inflammatory and chemotactic cytokines in cystathionine beta-synthase deficient homocystinuria.

Cystathionine beta-synthase (CBS) deficient homocystinuria (HCU) is an inherited metabolic defect that if untreated, typically results in cognitive impairment, connective tissue disturbances, atherosclerosis and thromboembolic disease. In recent years, chronic inappropriate expression of the inflammatory response has emerged as a major driving force of both thrombosis and atherosclerotic lesion development. We report here a characterization of the abnormalities in cytokine expression induced in both a mouse model of HCU and human subjects with the disease in the presence and absence of homocysteine lowering therapy. HCU mice exhibited highly significant induction of the pro-inflammatory cytokines Il-1alpha, Il-1beta and TNF-alpha. Similarly, in untreated/poorly compliant human subjects with HCU we observed constitutive induction of multiple pro-inflammatory cytokines (IL-1alpha, IL-6, TNF-alpha, Il-17 and IL-12(p70)) and chemotactic chemokines (fractalkine, MIP-1alpha and MIP-1beta) compared to normal controls. These HCU patients also exhibited significant induction of IL-9, TGF-alpha and G-CSF. The expression levels of anti-inflammatory cytokines were unaffected in both HCU mice and human subjects with the disease. In the human subjects, homocysteine lowering therapy was associated with either normalization or significant reduction of all of the pro-inflammatory cytokines and chemokines investigated. We conclude that HCU is a disease of chronic inflammation and that aberrant cytokine expression has the potential to contribute to multiple aspects of pathogenesis. Our findings indicate that anti-inflammatory strategies could serve as a useful adjuvant therapy for this disease.

Outcome after three years of laronidase enzyme replacement therapy in a patient with Hurler syndrome

Summary Enzyme replacement therapy (ERT) with laronidase, recombinant α-l-iduronidase, for mucopolysaccharidosis type I (MPS I) has been clinically available since April 2003. Pre-approval studies were performed on patients with the more attenuated forms of MPS I, Hurler–Scheie and Scheie syndromes. The clinical efficacy of laronidase on the severe form of MPS I, Hurler syndrome, is not well known. We present a patient with Hurler syndrome who has been treated with laronidase for 3 years. Clinically, the patient demonstrated improvement in urinary glycosaminoglycan (GAG) levels and hepatomegaly, but continued to experience decline in respiratory status, musculoskeletal and spinal involvement, and developmental skills. Overall, the benefit of ERT with laronidase in advanced Hurler syndrome appeared to be minimal in this patient.

Hunter-McAlpine craniosynostosis phenotype associated with skeletal anomalies and interstitial deletion of chromosome 17q

Hunter-McAlpine syndrome is an autosomal dominant disorder consisting of variable manifestations including craniosynostosis, almond-shaped palpebral fissures, small mouth, mild acral-skeletal anomalies, short stature, and mental deficiency. We report on a 9-year-old boy with this phenotype with more severe skeletal abnormalities than previously described. Chromosomes showed del(17)(q23.1-->q24.2); the more severe phenotype may be explained by the deletion. The deletion also suggests the possibility that the gene for Hunter-McAlpine syndrome might map to that region.

Mountain States Genetics Regional Collaborative Center's Metabolic Newborn Screening Long-term Follow-up Study: a collaborative multi-site approach to newborn screening outcomes research.

Purpose: This article presents the rationale and design of the Mountain States Genetics Regional Collaborative Centers Metabolic Newborn Screening Long-Term Follow-up Study.Methods: This study is a collaboration of multi-site metabolic providers throughout the Mountain States region investigating the long-term outcomes of individuals with metabolic conditions detected by newborn screening.Results: The Mountain States Genetics Regional Collaborative Centers Metabolic Consortium developed disease-specific care plans that included baseline and follow-up datasets for all metabolic disorders detected by both standard and tandem mass spectrometry newborn screening.Conclusion: These disease-specific care plans are used at multiple metabolic clinics throughout the Mountain States region. The shared datasets consisting of both performance and outcome indicators will be used to explore questions related to the treatment and outcome of these rare metabolic disorders. They will be used to assess the impact of newborn screening by comparing those individuals detected by newborn screening with those individuals diagnosed clinically, therefore allowing the systematic investigation of factors that impact long-term outcome.