S-adenosylhomocysteine hydrolase deficiency in a 26-year-old man.

This paper reports the third proven human case of deficient S-adenosylhomocysteine (AdoHcy) hydrolase activity. The patient is similar to the only two previously reported cases with this disorder in having severe myopathy, developmental delay, elevated serum creatine kinase (CK) concentrations, and hypermethioninaemia. Although he has been followed from infancy, the basic enzyme deficiency was established only at age 26 years. The diagnosis was based on markedly elevated plasma concentrations of both AdoHcy and S-adenosylmethionine, some 20% of the mean control activity of AdoHcy hydrolase activity in haemolysates of his red-blood cells, and two missense mutations in his gene encoding AdoHcy hydrolase. He had low values of erythrocyte phosphatidylcholine and plasma free choline and marginally elevated excretion of guanidinoacetate, suggesting that the elevated AdoHcy may have been inhibiting methylation of phosphatidylethanolamine and guanidinoacetate. His leukocyte DNA was globally more methylated than the DNA's of his parents or the mean extent of methylation measured in age-matched control subjects.

Two adult galactosaemia females with normal ovarian function and identical GALT mutations (Q188R/R333G).

We report two unrelated cases of adult galactosaemia females with normal ovarian function and Q188R/R333G mutations. Clinical history has been followed for 40 years. Biochemical finding in one patient are consistent with the presence of small amounts of galactose-1-phosphate uridyltransferase (GALT) activity, which differs from classical galactosaemia.

Mitochondrial encephalomyopathy and complex III deficiency associated with a stop-codon mutation in the cytochrome b gene.

We have reinvestigated a young woman, originally reported by us in 1983, who presented with exercise intolerance and lactic acidosis associated with severe deficiency of complex III and who responded to therapy with menadione and ascorbate. Gradually, she developed symptoms of a mitochondrial encephalomyopathy. Immunocytochemistry of serial sections of muscle showed a mosaic of fibers that reacted poorly with antibodies to subunits of complex III but reacted normally with antibodies to subunits of complexes I, II, or IV, suggesting a mutation of mtDNA. These findings demonstrate the diagnostic value of immunocytochemistry in identifying specific respiratory-chain deficiencies and, potentially, distinguishing between nuclear- or mtDNA-encoded defects. Sequence analysis revealed a stop-codon mutation (G15242A) in the mtDNA-encoded cytochrome b gene, resulting in loss of the last 215 amino acids of cytochrome b. PCR-RFLP analysis indicated that the G15242A mutation was heteroplasmic and was present in a high percentage (87%) of affected tissue (skeletal muscle) and a low percentage (0.7%) of unaffected tissue (blood) but was not detected in controls. Analysis of microdissected muscle fibers showed a significant correlation between the immunoreactivity toward the Rieske protein of complex III and the percentage of mutant mtDNA: immunopositive fibers had a median value of 33% of the G15242A mutation, whereas immunonegative, ragged-red fibers had a median value of 89%, indicating that the stop-codon mutation was pathogenic in this patient. The G15242A mutation was also present in several other tissues, including hair roots, indicating that it must have arisen either very early in embryogenesis, before separation of the primary germ layers, or in the maternal germ line. The findings in this patient are contrasted with other recently described patients who have mutations in the cytochrome b gene.

Cardiomyopathy in childhood, mitochondrial dysfunction, and the role of L-carnitine.

Cardiomyopathy in childhood is associated with high morbidity and mortality rates. Many metabolic causes have been identified, including genetic or acquired defects in mitochondrial energy production affecting beta-oxidation, carnitine transport, and the electron transport chain. Combining conventional inotropic and antiarrhythmic therapy with metabolic interventions has improved overall outcome. L-carnitine, a natural substance involved in mitochondrial transport of fatty acids, is one such therapy and plays a central role in the regulation of the inner mitochondrial supply of free coenzyme A. Carnitine deficiency can be caused by both genetic and environmental causes with resultant signs and symptoms of metabolic disease, including cardiomyopathy. Administration of L-carnitine can result in improvement or resolution of the cardiomyopathy.

D-2-Hydroxyglutaric aciduria: biochemical marker or clinical disease entity?

D-2-Hydroxyglutaric aciduria has been observed in patients with extremely variable clinical symptoms, creating doubt about the existence of a disease entity related to the biochemical finding. An international survey of patients with D-2-hydroxyglutaric aciduria was initiated to solve this issue. The clinical history, neuroimaging, and biochemical findings of 17 patients were studied. Ten of the patients had a severe early-infantile-onset encephalopathy characterized by epilepsy, hypotonia, cerebral visual failure, and little development. Five of these patients had a cardiomyopathy. In neuroimaging, all patients had a mild ventriculomegaly, often enlarged frontal subarachnoid spaces and subdural effusions, and always signs of delayed cerebral maturation. In all patients who underwent neuroimaging before 6 months, subependymal cysts over the head or corpus of the caudate nucleus were noted. Seven patients had a much milder and variable clinical picture, most often characterized by mental retardation, hypotonia, and macrocephaly, but sometimes no related clinical problems. Neuroimaging findings in 3 patients variably showed delayed cerebral maturation, ventriculomegaly, or subependymal cysts. Biochemical findings included elevations of D-2-hydroxyglutaric acid in urine, plasma, and cerebrospinal fluid in both groups. Cerebrospinal fluid gamma-aminobutyric acid was elevated in almost all patients investigated. Urinary citric acid cycle intermediates were variably elevated. The conclusion of the study is that D-2-hydroxyglutaric aciduria is a distinct neurometabolic disorder with at least two phenotypes.

Mutations in the liver glycogen synthase gene in children with hypoglycemia due to glycogen storage disease type 0.

Glycogen storage disease type 0 (GSD-0) is a rare form of fasting hypoglycemia presenting in infancy or early childhood and accompanied by high blood ketones and low alanine and lactate concentrations. Although feeding relieves symptoms, it often results in postprandial hyperglycemia and hyperlactatemia. The glycogen synthase (GS) activity has been low or immeasurable in liver biopsies, whereas the liver glycogen content has been only moderately decreased. To investigate whether mutations in the liver GS gene (GYS2) on chromosome 12p12.2 were involved in GSD-0, we determined the exon-intron structure of the GYS2 gene and examined nine affected children from five families for linkage of GSD-0 to the GYS2 gene. Mutation screening of the 16 GYS2 exons was done by single-strand conformational polymorphism (SSCP) and direct sequencing. Liver GS deficiency was diagnosed from liver biopsies (GS activity and glycogen content). GS activity in the liver of the affected children was extremely low or nil, resulting in subnormal glycogen content. After suggestive linkage to the GYS2 gene had been established (LOD score = 2.9; P < 0.01), mutation screening revealed several different mutations in these families, including a premature stop codon in exon 5 (Arg246X), a 5'-donor splice site mutation in intron 6 (G+1T--> CT), and missense mutations Asn39Ser, Ala339Pro, His446Asp, Pro479Gln, Ser483Pro, and Met491Arg. Seven of the affected children carried mutations on both alleles. The mutations could not be found in 200 healthy persons. Expression of the mutated enzymes in COS7 cells indicated severely impaired GS activity. In conclusion, the results demonstrate that GSD-0 is caused by different mutations in the GYS2 gene.

Inborn errors of metabolism: medical and administrative "orphans".

CONTEXT: Inborn errors of metabolism are genetic conditions that affect the normal biochemical functions of the body in any organ and at any age. More than 500 metabolic diseases are known; almost all are classified as orphan diseases under the US Food and Drug Administration guidelines (incidence < 200,000 persons) and each has its own requirements for diagnosis and treatment. Management of these complex, lifelong, multisystem disorders often requires a coordinated, multidisciplinary approach involving several subspecialists and which may include complex laboratory evaluations, genetic counseling, nutritional therapy, and unusual therapeutic approaches that have been used in only a small number of cases. RESULTS: Not infrequently, inborn errors of metabolism fall outside current standard diagnostic and treatment guidelines of managed care plans. This results in delays in diagnosis and appropriate management, with increased costs to patients and to society. CONCLUSIONS: Patients with inborn errors of metabolism should not be discriminated against and all health plans should specify that access to specialists and metabolic centers are a covered benefit of the plan. The acceptance of treatment guidelines, the development of international disease classification codes for the disorders, and the performance of cost-benefit analyses would all greatly facilitate this process. However, without recognition that these disorders require such services, and steps to provide them by the insurance industry, the care of children with metabolic disorders and other chronic diseases will continue to be a source of frustration and anger among the caregivers and the families they serve.

Outcome of pyruvate dehydrogenase deficiency treated with ketogenic diets. Studies in patients with identical mutations.

Inborn errors of the pyruvate dehydrogenase complex (PDC) are associated with lactic acidosis, neuroanatomic defects, developmental delay, and early death. PDC deficiency is a clinically heterogeneous disorder, with most mutations located in the coding region of the X-linked alpha subunit of the first catalytic component, pyruvate dehydrogenase (E1). Treatment of E1 deficiency hs included cofactor replacement, activation of PDC with dichloroacetate, and ketogenic diets. In this report, we describe the outcome of ketogenic diet treatment in seven boys with E1 deficiency. These patients were divided into two groups based on their mutations (R349H, three patients; and R234G, four patients, two sibling pairs). All seven patients received ketogenic diets with varying degrees of carbohydrate restriction. Clinical outcome was compared within each group and between siblings as related to the intensity and duration of dietary intervention. Subjects who either had the diet initiated earlier in life or who were placed on greater carbohydrate restriction had increased longevity and improved mental development. Based on the improved outcomes of patients with identical mutations, it appears that a nearly carbohydrate-free diet initiated shortly after birth may be useful in the treatment of E1 deficiency.

Treatment products and approaches for phenylketonuria: improved palatability and flexibility demonstrate safety, efficacy and acceptance in US clinical trials.

A new amino acid formulation and a variety of treatment products incorporating it were evaluated for long-term safety, efficacy, and acceptance in 25 subjects with phenylketonuria over a period of 5 years. Palatability of the treatment was improved by reducing the required intake of amino acids, reformulating the mixture to have better taste, and providing vitamins and minerals as tablets. The hypotheses were that these strategies would improve compliance and metabolic control and maintain nutritional status in subjects. Compliance with treatment was determined from mean reported intakes (4-day diet records) and from mean 'received' intakes using receipts of treatment products actually shipped to individuals upon request. Mean amino acid intakes prescribed were significantly reduced from study entry to end, from 1.2 g/kg to 0.7 g/kg (p < 0.001). Reported intakes were similarly reduced from 1.3 g/kg to 0.7 g/kg (p < 0.001). While actually 'received' intakes of amino acid formula were also significantly reduced (p < 0.001), intakes by this measure were much lower than either prescribed or reported, 0.9 g/kg at entry and 0.4 g/kg at the end of the study, suggesting that acceptance of the treatment (usage of products), even when made more palatable, is below clinical expectations. In spite of these findings, mean serum proteins and minerals, height and weight were not significantly reduced during the study, supporting the safety of lowered intakes of amino acids and of nutritionally incomplete products. While the increase in mean serum phenylalanine concentration from 0.38 to 0.48 mmol/L was significant (p < 0.03), this mean rise of 0.1 mmol/L during a corresponding mean age increase of 4.2 years (from 6.9 to 11.1 years) is lower than in other recent reports from longitudinal studies of outcomes during this age range in subjects treated with traditional products. These data support the safety and efficacy of a more palatable and flexible approach to treatment.

Molecular analysis of the beta-glucuronidase gene: novel mutations in mucopolysaccharidosis type VII and heterogeneity of the polyadenylation region.

We used polymerase chain reaction (PCR)/single-strand conformation polymorphism analysis and direct sequencing of the coding region of the beta-glucuronidase cDNA and gene to detect mutations causing beta-glucuronidase enzyme deficiency in five MPS VII patients. Four patients presented with hydrops fetalis, one with an early infantile form of the disease. Genetic heterogeneity of MPS VII alleles was further confirmed in this study. Recurrent mutations were observed in patients of related origin. Previously unknown alleles detected were RII0X, F361delta9, 1270 + 1G-->A, S52F and 1480delta4. Reverse transcription/PCR analysis of the 1270 + 1G-->A messenger showed aberrant splicing: inclusion of intron 7 or skipping of exons 6-7 and 9. Messenger RNA transcribed from the R110X and 1480delta4 alleles was unstable. We detected a 2154A/G change in the 3' non-coding region of the gene, in the neighbourhood of the two consensus polyadenylation sites. 3'-Rapid amplification of cDNA ends/PCR of fibroblast cDNA revealed equal usage of two alternative polyadenylation sites. The 2154A/G substitution did not influence adenylation-site choice, nor the amount of stable messenger produced. The finding that 2 out of 30 normal controls carried the 2154G allele indicated that the 2154A/G substitution is a harmless polymorphism. The S52F and F361delta9 cDNAs were constructed in vitro and used to transfect COS cells transiently. Both mutations completely abolished enzyme activity.

Clustered inactivating mutations and benign polymorphisms of the calcium receptor gene in familial benign hypocalciuric hypercalcemia suggest receptor functional domains.

The predominant variety of familial benign hypocalciuric hypercalcemia (FBHH) is FBHH(3q), which is associated with presumed inactivating mutations of the cell surface calcium receptor (CaR) gene on chromosome 3q13.3-q21. We sought mutations of the CaR gene in FBHH by direct sequencing of PCR-amplified genomic DNA from 14 affected families: 8 mapped to 3q13, 1 mapped to chromosome 19p, and 5 unmapped. We sequenced the entire coding region of the gene (exons 2-7) in one or two affected members of each family and found six point mutations that altered one amino acid, cosegregated with hypercalcemia, and were absent in more than 100 unaffected persons. Four mutations were unique (S53P, D215G, S657Y, and P748R), and two had been reported previously (P55L and R185Q). Of four mutant CaR proteins expressed in Xenopus oocytes, three were deficient in extracellular Ca2+-induced signaling. No CaR mutations were found in eight families, including the one mapped to chromosome 19p. Three benign polymorphisms occurred in the COOH-terminal region of the CaR protein in 10%, 15%, and 30% of more than 100 unaffected persons. Thus, FBHH-causing CaR mutations were clustered in the NH2-terminal extracellular and membrane-spanning regions of the receptor protein. We suggest that these are important functional domains, probably for calcium binding and signal transduction, respectively. Finally, mutations in regulatory or intronic regions of the CaR gene may also underlie many cases of FBHH.

A microdeletion in cytochrome c oxidase (COX) subunit III associated with COX deficiency and recurrent myoglobinuria.

We have identified a 15-bp microdeletion in a highly conserved region of the mitochondrially encoded gene for cytochrome c oxidase (COX) subunit III in a patient with severe isolated COX deficiency and recurrent myoglobinuria. The mutant mitochondrial DNA (mtDNA) comprised 92% of the mtDNA in muscle and 0.7% in leukocytes. Immunoblots and immunocytochemistry suggested a lack of assembly or instability of the complex. Microdissected muscle fibres revealed significantly higher portions of mutant mtDNA in COX-negative than in COX-positive fibres. This represents the first case of isolated COX deficiency to be defined at the molecular level.

Early copper therapy in classic Menkes disease patients with a novel splicing mutation.

To correlate genotype with response to early copper histidine therapy in Menkes disease, an X-linked disorder of copper transport, we performed mutational analysis in 2 related males who began treatment at the age of 10 days and prenatally at 32 weeks' gestation, respectively. A G to T transversion at the -1 exonic position of a splice donor site was identified, predicting a glutamine to histidine substitution at codon 724 of the Menkes copper-transporting ATPase gene. The Q724H mutation disrupts proper splicing and generates five mutant transcripts that skip from one to four exons. None of these transcripts is predicted to encode a functional copper transport protein. Copper histidine treatment normalized circulating copper and ceruloplasmin levels but did not improve the baseline deficiency of dopamine-beta-hydroxylase, a copper-dependent enzyme. At the age of 36 months, the first patient was living and had neurodevelopmental abilities ranging from 10 to 15 months. The second patient also showed delayed neurodevelopment and died of pulmonary complications at the age of 5 1/2 months. We conclude that early copper histidine therapy does not normalize neurological outcome in patients with the Q724H splicing mutation, and suggest that preservation of some residual Menkes ATPase activity may be a general prerequisite for significant clinical efficacy from such treatment.

A clinical approach to inborn errors of metabolism.

Asking physicians to diagnose and treat all varieties of inborn errors or metabolism, without access to an extensive and experienced laboratory, is rather like asking a surgeon to perform his job without a scalpel. Nonetheless, astute clinicians armed with knowledge of the clinical manifestations of these disorders and using some simple algorithms can achieve considerable success although it should be said that tentative and unconfirmed diagnoses can be dangerous both for the patient and for use in genetic counseling. For these reasons it seems critical that areas of the world, such as Southeast Asia, where many of the countries have sophisticated medical systems, should develop regional services which can provide the contemporary procedures critical for accurate diagnosis of inborn errors of metabolism. In either case, the financial costs are substantial (Table 12).

A new amino acid mixture permits new approaches to the treatment of phenylketonuria.

A new amino acid mixture for incorporation into medical foods for the treatment of hyperphenylalaninemia has been tested in a regular clinic. The mix is designed to be as unobtrusive as possible, consistent with good nutrition. After more than 1 year of trial as a beverage, we have shown that it is safe and well tolerated but that plasma phenylalanine is no better controlled than with some other products. The mix can be incorporated into a large number of different foods without affecting the taste. Occult monitoring of the quantity of medical foods purchased compared with the amounts reported to be consumed in diet histories provides an excellent way to monitor dietary compliance.

A rippling muscle disease gene is localized to 1q41: evidence for multiple genes.

Rippling muscle disease (RMD) is an inherited disorder of skeletal muscle in which mechanical stimuli provoke electrically silent contractions. Patient symptoms are muscle cramps, pain, and stiffness, particularly during or following exercise. Clinical signs are balling of muscle following percussion and a characteristic lateral rolling movement of muscle occurring after contraction followed by stretching. We report a new 44-member pedigree segregating RMD as an autosomal dominant trait. A genetic linkage study in this family, using a novel approach of testing closely spaced highly polymorphic markers in affected individuals, localized the responsible gene to the distal end of the long arm of chromosome 1 with a maximum multipoint lod score of 3.56 (theta = 0). In this family, RMD is localized to a 12-cM region near D1S235. We studied two previously reported German families for linkage to the same locus, and this same area did not cosegregate with the disease, a finding that shows that different genetic defects can cause a similar clinical phenotype (genetic heterogeneity). An understanding of the defect in contraction control within the muscle fibers in this disease may lead to a better understanding of muscle force transduction, intracellular calcium homeostasis, or both.