A new genetic disorder in mitochondrial fatty acid beta-oxidation: ACAD9 deficiency

The acyl-CoA dehydrogenases are a family of multimeric flavoenzymes that catalyze the alpha,beta -dehydrogenation of acyl-CoA esters in fatty acid beta -oxidation and amino acid catabolism. Genetic defects have been identified in most of the acyl-CoA dehydrogenases in humans. Acyl-CoA dehydrogenase 9 (ACAD9) is a recently identified acyl-CoA dehydrogenase that demonstrates maximum activity with unsaturated long-chain acyl-CoAs. We now report three cases of ACAD9 deficiency. Patient 1 was a 14-year-old, previously healthy boy who died of a Reye-like episode and cerebellar stroke triggered by a mild viral illness and ingestion of aspirin. Patient 2 was a 10-year-old girl who first presented at age 4 mo with recurrent episodes of acute liver dysfunction and hypoglycemia, with otherwise minor illnesses. Patient 3 was a 4.5-year-old girl who died of cardiomyopathy and whose sibling also died of cardiomyopathy at age 21 mo. Mild chronic neurologic dysfunction was reported in all three patients. Defects in ACAD9 mRNA were identified in the first two patients, and all patients manifested marked defects in ACAD9 protein. Despite a significant overlap of substrate specificity, it appears that ACAD9 and very-long-chain acyl-CoA dehydrogenase are unable to compensate for each other in patients with either deficiency. Studies of the tissue distribution and gene regulation of ACAD9 and very-long-chain acyl-CoA dehydrogenase identify the presence of two independently regulated functional pathways for long-chain fat metabolism, indicating that these two enzymes are likely to be involved in different physiological functions.

Case report: liver glycogen synthase deficiency--a cause of ketotic hypoglycemia

Glycogen synthase deficiency is a rare inborn error of metabolism, characterized by fasting hypoglycemia, hypoglycemic seizures, and ketonuria. Only 7 families with 14 affected children have been reported. Here, we report an additional patient with this deficiency. Findings in this patient were clinically and biochemically consistent with those reported in patients with ketotic hypoglycemia and may alert the clinician to consider glycogen synthase deficiency.

Acute hydrocephalus in nonketotic hyperglycinemia

We present four patients with typical neonatal onset non-ketotic hyperglycinemia (NKH) who developed hydrocephalus requiring shunting in early infancy. Brain imaging revealed acute hydrocephalus, a megacisterna magna or posterior fossa cyst, pronounced atrophy of the white matter, and an extremely thin corpus callosum in all. The three older patients had profound developmental disabilities. This suggests that the development of hydrocephalus in NKH is an additional poor prognostic sign.

Molecular and clinical studies in SCA-7 define a broad clinical spectrum and the infantile phenotype

OBJECTIVE

To screen for the SCA-7 mutation in autosomal dominant cerebellar ataxia (ADCA) families and study genotype/phenotype correlations.

BACKGROUND

The association of cerebellar ataxia and progressive pigmentary macular dystrophy clinically defines a distinct form of ADCA classified as SCA-7. SCA-7 is caused by expansion of a highly unstable CAG repeat that lies in the coding region of a novel gene on chromosome 3p12-13.

METHODS

We screened 51 ADCA kindreds, in which SCA-1, SCA-2, SCA-3, and SCA6 mutations had been excluded, for the SCA-7 mutation using primers that specifically amplify the SCA-7 CAG repeat.

RESULTS

The SCA-7 mutation was identified in 10 independent families. Normal alleles ranged from 7 to 16 repeats; expanded alleles ranged from 41 to 306 repeats. One allele with 36 repeats was found in an asymptomatic individual carrying an at-risk haplotype. SCA-7 presents a wide spectrum of clinical features including visual loss, dementia, hypoacusia, severe hypotonia, and auditory hallucinations. Juvenile SCA-7 occurs on maternal and paternal transmission of the mutation, whereas the infantile form occurs only on paternal transmission. An infant of African American descent carried the largest SCA-7 expansion (306 CAG repeats) and had severe hypotonia, congestive heart failure, patent ductus arteriosus, cerebral and cerebellar atrophy, and visual loss.

CONCLUSION

These data show a wide spectrum of phenotypic abnormalities in SCA-7 and define an infantile phenotype caused by the largest CAG repeat expansion described to date.

Rasmussen syndrome and long-term response to gamma globulin

Rasmussen syndrome (RS) is a severe and progressive focal epilepsy of unknown etiology that leads to deterioration of motor and cognitive function. We report a 14-year-old girl who developed epilepsia partialis continua involving the left hand, mild hemiparesis, and secondarily generalized seizures. RS was confirmed by brain biopsy. The patient has been treated with intravenous gamma globulin every 4 months for 46 months. The clinical course throughout this time has been distinctly atypical for RS, with no progression in motor or cognitive deficits and rare secondarily generalized seizures. Although the mechanism for action for gamma globulin in RS is not known, an immunomodulatory role has been postulated. Evidence of an immunologically mediated process in RS and clinical experience with a growing number of patients who benefit from immunomodulatory therapy suggest that a systematic study of the efficacy of gamma globulin in comparison with other forms of medical therapy is warranted.

Chromosome 1p terminal deletion: report of new findings and confirmation of two characteristic phenotypes

We report three unrelated patients with small terminal deletions involving 1p36.22-->pter that occurred de novo and compare our patients to the 10 previously reported cases. Although our patients have an identical cytogenetic deletion, patients 1 and 2 share similar clinical features that differ substantially from patient 3. Our patients confirm the existence of two characteristic phenotypes in 1p36.22-->pter deletion. Both phenotypes share some dysmorphic features, but are differentiated by characteristics of growth failure versus macrosomia. In addition, we report the new finding of cardiomyopathy and hydrocephalus in the phenotype associated with growth failure. It is possible that different phenotypic subgroups may exist because of differences in the parental origins of the deleted chromosome or of variations in undetectable amounts of genetic material.

SPECT abnormalities in generalized dystonia

A patient with severe, generalized dystonia and 6 age range-matched controls were studied with the regional cerebral blood flow tracer technetium-99m hexamethylpropyleneamine oxime by single-photon emission computed tomography to test the hypothesis that cerebellar function is abnormal in dystonia. Analysis was performed by drawing regions of interest around the caudate head nuclei, hemithalami, deep cerebellar nuclei, and cerebellar hemicortices. The counts in each region of interest were normalized to whole brain cerebral blood flow in an identical manner for each subject. The dystonic patient had a difference in regional cerebral blood flow between the right and left deep cerebellar nuclei, increased regional cerebral blood flow in subcortical motor structures, and an abnormal relationship between right cerebellar cortical and right deep cerebellar nuclear regional cerebral blood flow. The findings in this patient provide evidence that the cerebellum may play a role in the pathophysiology of motor signs in some patients with dystonia.

Retinal degeneration characterizes a spinocerebellar ataxia mapping to chromosome 3p

A heterogeneous group of neurological disorders known as the spinocerebellar ataxias (SCA) are characterized by degeneration of the cerebellum, spinal cord and brainstem. We describe linkage analysis in four unusual SCA families revealing a distinct disease locus on chromosome 3p14-21.1. The disease in these families is distinguished from other forms of SCA by concomitant retinal degeneration. Initial visual problems leading to blindness, disabling ataxia and anticipation are seen in all kindreds. The anticipation in these families suggests a dynamic mutation at this locus. Eventual molecular characterization of this disease may provide valuable insights into the processes of both neural and retinal degeneration.

3-Hydroxyisovalerylcarnitine in 3-methylcrotonyl-CoA carboxylase deficiency

A new acylcarnitine was observed in the plasma and urine of a patient with isolated 3-methylcrotonyl-CoA carboxylase deficiency. Analysis by tandem mass spectrometry of the methyl ester and butyl ester and their fragment ion spectra identified it as a 3-hydroxy-C5-acylcarnitine. Fibroblasts from a second patient were incubated with deuterium-labelled leucine. Incorporation of label in the new acylcarnitine identified its origin from leucine, and thus confirmed the structure as 3-hydroxyisovalerylcarnitine. The presence of elevated amounts of this metabolite, plus a small amount of 3-methylcrotonylcarnitine in plasma, was diagnostic for isolated 3-methylcrotonyl-CoA carboxylase deficiency. Other conditions in which a hydroxy-C5-acylcarnitine was present were readily differentiated by the abnormal elevation of other acylcarnitines.

Glycine and L-carnitine therapy in 3-methylcrotonyl-CoA carboxylase deficiency

Genetic deficiency of 3-methylcrotonyl-CoA carboxylase (3-MCC) is a rare inborn error of leucine metabolism producing an organic acidaemia. With accumulation of 3-methylcrotonyl-CoA, there is increased production of 3-hydroxyisovaleric acid, the glycine conjugate (3-methylcrotonylglycine), and the carnitine conjugate (3-hydroxyisovalerylcarnitine). The conjugates represent endogenous detoxification products. We studied excretion rates of these conjugates at baseline and with glycine and carnitine therapy in an 8-year-old girl with 3-MCC deficiency. Her preadmission diet was continued. Plasma and urine samples were obtained after 24 h of each of the following: L-carnitine 100 mg/kg per day and glycine 100, 175 and 250 mg/kg per day. Plasma and urinary carnitine levels were reduced by 80% and 50%, respectively with abnormal urinary excretion patterns. These normalized with carnitine therapy. Acylcarnitine excretion increased with carnitine therapy. The glycine conjugate, 3-methylcrotonylglycine (3-MCG), was the major metabolite excreted at all times and its excretion increased with glycine therapy. Clearly, in 3-MCC deficiency the available glycine and carnitine pools are not sufficient to meet the potential for conjugation of accumulated metabolites, suggesting a possible therapeutic role for glycine and carnitine therapy in this disorder.

Tubulointerstitial nephritis in methylmalonic acidemia

We report two patients with methylmalonic acidemia (MMA) in whom renal biopsy demonstrated interstitial nephritis, bringing the total of such reported cases to four. In addition, hypertension, observed in one of our patients, has not been previously reported as the presentation of renal disease in MMA. The etiology of interstitial nephritis in MMA did not appear to be due to urate nephropathy. To date, 15 patients with MMA have been reported with renal complications, including chronic renal failure, making it imperative that children with MMA have their renal status evaluated.

Molecular basis of inherited medium-chain acyl-CoA dehydrogenase deficiency causing sudden child death

Deficiency of medium-chain acyl-CoA dehydrogenase (MCAD) is an important cause of sudden death in children. The majority of surviving individuals with MCAD deficiency studied to date are homozygous for a single point mutation at bp 985 of the MCAD mRNA (A985G). We have now identified a four-base-pair deletion in exon 11 of one allele of the MCAD gene in an American child who died of MCAD deficiency. The deletion mutation results in a frameshift and premature termination codon in the mutant MCAD mRNA. The second mutant allele contained the common point mutation A985G, and thus the proband was a compound heterozygote. Protein immunoblot analysis of the child's liver proteins revealed that the mutant MCAD proteins were barely detectable. Allele-specific oligonucleotide hybridization analysis performed on amplified exon 11 of the child's MCAD gene clearly identified both mutations. MCAD RFLP analysis of the patient's DNA revealed heterozygosity at the Taq I MCAD RFLP site, thus, the two mutations are associated with different haplotypes. Therefore, we have identified a new mutation in the MCAD gene and have developed a nucleic-acid-based screening approach which allows the post mortem identification of MCAD deficiency.

Heteroplasmy in chronic external ophthalmoplegia: clinical and molecular observations

Chronic progressive external ophthalmoplegia (CPEO) describes a recognizable clinical syndrome frequently associated with variable dysfunction in other organ systems. Histochemical and biochemical studies suggested primary dysfunction of oxidative phosphorylation. This has recently been confirmed by demonstration of partially deleted as well as normal mitochondrial DNA--heteroplasmy--in some of these patients, most of them sporadic. In the six heteroplasmic CPEO patients that we have examined to date, the partially deleted species has been detected in all tissues tested, albeit in vastly different proportions. We report here detection of physiologically significant proportions of partially deleted mitochondrial DNA in several organs taken at autopsy from a CPEO patient with severe multisystem disease. We discuss the relationship of CPEO to several other clinical phenotypes associated with mitochondrial dysfunction, and discuss the possible implications of heteroplasmy for the development of variable phenotypes.

Directly repeated sequences associated with pathogenic mitochondrial DNA deletions

We determined the nucleotide sequences of junctional regions associated with large deletions of mitochondrial DNA found in four unrelated individuals with a phenotype of chronic progressive external ophthalmoplegia. In each patient, the deletion breakpoint occurred within a directly repeated sequence of 13-18 base pairs, present in different regions of the normal mitochondrial genome-separated by 4.5-7.7 kilobases. In two patients, the deletions were identical. When all four repeated sequences are compared, a consensus sequence of 11 nucleotides emerges, similar to putative recombination signals, suggesting the involvement of a recombinational event. Partially deleted and normal mitochondrial DNAs were found in all tissues examined, but in very different proportions, indicating that these mutations originated before the primary cell layers diverged.

Pyruvate carboxylase deficiency: acute exacerbation after ACTH treatment of infantile spasms

Pyruvate carboxylase deficiency results in congenital lactic acidosis. We report the significant finding in a child with infantile spasms controlled with adrenocorticotrophin hormone (ACTH) but who then developed severe lactic acidosis; pyruvate carboxylase deficiency was subsequently diagnosed. Blood lactate, pyruvate, and alanine levels were elevated, as well as cerebrospinal fluid alanine. Plasma alanine concentration was doubled by ACTH therapy. Fibroblasts contained extremely low pyruvate carboxylase activity. The patient died at 12 weeks of age after recurrent episodes of profound acidosis. At autopsy, the brain manifested cystic degeneration and demyelination. Pyruvate carboxylase deficiency is associated with neonatal onset of acidosis, delayed development, seizures, hypotonia, recurrent profound acidosis, and early death. The dramatic rise in plasma alanine content coincident with ACTH therapy suggest that ACTH played a role in precipitating the catastrophic metabolic acidosis.

Brain tumors presenting as a seizure disorder in infants

Seizures occur in 25% to 40% of children with supratentorial tumors and are the presenting complaint in 10% to 15%. However, when divided by age, only 2% of children with seizures as the presenting complaint of brain tumors were less than 1 year of age. Three children, ranging in age from 20 days to 7 months and seen within the past 2 years, form the basis of this report. The presenting complaint in all children was seizures. Computed tomographic (CT) scan was indicated in all children because of intractability to anticonvulsant drug therapy (one patient) and focal electroencephalographic (EEG) abnormality with clinical evidence of complex partial seizure activity (two patients). CT scan showed a contrast-enhancing mass in the medial temporal lobe in all patients. At surgery, a temporal lobe tumor was found and resected in all children. Histopathologic examination revealed a ganglioglioma, a fibrillary astrocytoma, and an anaplastic astrocytoma. All children did well postoperatively and are seizure free to date. Our experience suggests that supratentorial tumors should be considered as a cause of intractable and/or focal seizures in children under 1 year of age, and that such tumors should be attacked aggressively neurosurgically. Our experience is also in agreement with that of Tadmor et al, who have suggested that with the advent of CT scanning supratentorial tumors in this age group have been found to be more common than previously realized.

Neurologic complications of immunizations

Although there does appear to be at least a temporal relationship between pertussis immunization and serious acute neurologic illness, data to suggest that children with stable preexisting neurologic disease or positive family history of neurologic disease are at increased risk for complications of pertussis immunizations are inconclusive. Furthermore, there are no firm statistical data concerning the incidence of pertussis vaccine-related encephalopathy. Rather, the literature on pertussis vaccine complications is replete with anecdotal reports and retrospective studies with a number of questionable conclusions drawn from this inadequate data base. Unfortunately, these conclusions have been sensationalized and exploited with litigious fervor to the point that the practice of pertussis immunization is being questioned in the United States. A number of points should be reiterated: pertussis is a dangerous and deadly disease, as seen in the epidemic in Great Britain; pertussis immunization is effective in protecting against the disease; and there is no conclusive proof that the incidence of complications from pertussis vaccination of children with seizure disorders or other preexisting stable neurologic abnormalities is higher, because appropriate studies have not been done to define such a risk. We would do well to keep these facts in mind in order to avoid a disaster similar to the pertussis epidemic in Great Britain. Pertussis vaccination should be given to all children except those with allergic hypersensitivity, a progressive neurologic disorder, or an adverse reaction to a previous pertussis dose.