The role of human demographic history in determining the distribution and frequency of transferase-deficient galactosaemia mutations.

Classical or transferase-deficient galactosaemia is an inherited metabolic disorder caused by mutation in the human Galactose-1-phosphate uridyl transferase (GALT) gene. Of some 170 causative mutations reported, fewer than 10% are observed in more than one geographic region or ethnic group. To better understand the population history of the common GALT mutations, we have established a haplotyping system for the GALT locus incorporating eight single nucleotide polymorphisms and three short tandem repeat markers. We analysed haplotypes associated with the three most frequent GALT gene mutations, Q188R, K285N and Duarte-2 (D2), and estimated their age. Haplotype diversity, in conjunction with measures of genetic diversity and of linkage disequilibrium, indicated that Q188R and K285N are European mutations. The Q188R mutation arose in central Europe within the last 20 000 years, with its observed east-west cline of increasing relative allele frequency possibly being due to population expansion during the re-colonization of Europe by Homo sapiens in the Mesolithic age. K285N was found to be a younger mutation that originated in Eastern Europe and is probably more geographically restricted as it arose after all major European population expansions. The D2 variant was found to be an ancient mutation that originated before the expansion of Homo sapiens out of Africa.

Guideline for the diagnosis and management of glutaryl-CoA dehydrogenase deficiency (glutaric aciduria type I).

Glutaryl-CoA dehydrogenase (GCDH) deficiency is an autosomal recessive disease with an estimated overall prevalence of 1 in 100 000 newborns. Biochemically, the disease is characterized by accumulation of glutaric acid, 3-hydroxyglutaric acid, glutaconic acid, and glutarylcarnitine, which can be detected by gas chromatography-mass spectrometry of organic acids or tandem mass spectrometry of acylcarnitines. Clinically, the disease course is usually determined by acute encephalopathic crises precipitated by infectious diseases, immunizations, and surgery during infancy or childhood. The characteristic neurological sequel is acute striatal injury and, subsequently, dystonia. During the last three decades attempts have been made to establish and optimize therapy for GCDH deficiency. Maintenance treatment consisting of a diet combined with oral supplementation of L: -carnitine, and an intensified emergency treatment during acute episodes of intercurrent illness have been applied to the majority of patients. This treatment strategy has significantly reduced the frequency of acute encephalopathic crises in early-diagnosed patients. Therefore, GCDH deficiency is now considered to be a treatable condition. However, significant differences exist in the diagnostic procedure and management of affected patients so that there is a wide variation of the outcome, in particular of pre-symptomatically diagnosed patients. At this time of rapid expansion of neonatal screening for GCDH deficiency, the major aim of this guideline is to re-assess the common practice and to formulate recommendations for diagnosis and management of GCDH deficiency based on the best available evidence.

Short-chain acyl-CoA dehydrogenase deficiency associated with early onset severe axonal neuropathy.

Two unusual cases of axonal neuropathy associated with short-chain acyl-CoA dehydrogenase (SCAD) deficiency are described. These two unrelated infants presented with profound generalised weakness, particularly affecting the upper limbs. Clinical examination revealed generalised peripheral hypotonia and weakness, with absent deep tendon reflexes. An axonal polyneuropathy was confirmed on electromyogram (EMG) and nerve conduction studies (NCS) and, following an extensive metabolic screen, an acylcarnitine and organic acid profile consistent with a short-chain fatty acid beta-oxidation defect was found. In both cases, SCAD deficiency was confirmed by enzyme analysis. Genetic analysis showed the presence of common gene variations in the SCAD gene. SCAD deficiency is a rare disorder with a wide clinical phenotype. SCAD deficiency associated with axonal neuropathy has not previously been reported. As highlighted in these cases, it may be necessary to include axonal neuropathy as a presenting feature of SCAD.

Emergency treatment in glutaryl-CoA dehydrogenase deficiency.

The history of glutaryl-CoA dehydrogenase deficiency is determined by acute encephalopathic crises that are precipitated by common febrile diseases, vaccinations or surgical interventions during infancy and early childhood. Such crises result in an irreversible destruction of the basal ganglia (in particular of the putamina), and consequently dystonia, dyskinesia and choreoathetosis. Secondary complications include feeding and speech problems, failure to thrive, recurrent aspiration, immobilization, severe motor deficits and early death. It is generally accepted that maintenance treatment based on dietary lysine or protein restriction and supplementation with carnitine (and riboflavin) is insufficient to prevent acute crises during intercurrent illnesses or conditions that enhance catabolic state. Consequently, outpatient and inpatient emergency therapies have been implemented. The present review describes a recommended approach to emergency therapy for this disease.

Maintenance treatment of glutaryl-CoA dehydrogenase deficiency.

This paper summarizes the published experience as well as results of the 3rd International Workshop on Glutaryl-CoA Dehydrogenase Deficiency held in October 2003 in Heidelberg, Germany, on the topic treatment of patients with glutaryl-CoA dehydrogenase (GCDH) deficiency. So far no international recommendation for treatment of GCDH deficiency exists. Such an approach is hampered by several facts, namely the lack of an in-depth understanding of the pathophysiology of the disease, the lack of prospective studies, including the evaluation of drug monotherapy, and lack of objective documentation of clinical changes (e.g. video documentation) during pharmacotherapy.

Glutaric aciduria type I: outcome in the Republic of Ireland.

Twenty-one patients have been diagnosed with glutaric aciduria type I over a 16-year period in the Republic of Ireland, 11 following clinical presentation and 10 following a high-risk screen. Nineteen have been managed with diet. Eight patients have died, of whom 7 were diagnosed clinically. Six had dystonic and one spastic cerebral palsy. Of the 11 patients who did not have cerebral palsy, 10 were diagnosed following a high-risk screen. Seven of the 11 have no abnormal neurological signs; 6 of the 7 have abnormal CT or MRI findings; and no case of striatal degeneration has occurred during the past 14 years in the high-risk screened group.

Vascular outcome in patients with homocystinuria due to cystathionine beta-synthase deficiency treated chronically: a multicenter observational study.

An inborn error of metabolism, homocystinuria due to cystathionine beta-synthase deficiency, results in markedly elevated levels of circulating homocysteine. Premature vascular events are the main life-threatening complication. Half of all untreated patients have a vascular event by 30 years of age. We performed a multicenter observational study to assess the effectiveness of long-term homocysteine-lowering treatment in reducing vascular risk in 158 patients. Vascular outcomes were analyzed and effectiveness of treatment in reducing vascular risk was evaluated by comparison of actual to predicted number of vascular events, with the use of historical controls from a landmark study of 629 untreated patients with cystathionine beta-synthase deficiency. The 158 patients had a mean (range) age of 29.4 (4.5 to 70) years; 57 (36%) were more than 30 years old, and 10 (6%) were older than 50 years. There were 2822 patient-years of treatment, with an average of 17.9 years per patient. Plasma homocysteine levels were markedly reduced from pretreatment levels but usually remained moderately elevated. There were 17 vascular events in 12 patients at a mean (range) age of 42.5 (18 to 67) years: pulmonary embolism (n=3), myocardial infarction (n=2), deep venous thrombosis (n=5), cerebrovascular accident (n=3), transient ischemic attack (n=1), sagittal sinus thrombosis (n=1), and abdominal aortic aneurysm (n=2). Without treatment, 112 vascular events would have been expected, for a relative risk of 0.09 (95% CI 0.036 to 0.228; P<0.0001). Treatment regimens designed to lower plasma homocysteine significantly reduce cardiovascular risk in cystathionine beta-synthase deficiency despite imperfect biochemical control. These findings may be relevant to the significance of mild hyperhomocysteinemia that is commonly found in patients with vascular disease.

The intellectual abilities of early-treated individuals with pyridoxine-nonresponsive homocystinuria due to cystathionine beta-synthase deficiency.

The pathological sequelae of untreated homocystinuria due to cystathionine beta-synthase deficiency include ectopia lentis, osteoporosis, thromboembolic events and mental retardation. They occur at a significantly higher rate with poorer mental capabilities (mean IQ = 57) in the untreated pyridoxine-nonresponsive individuals. The mental capabilities of 23 pyridoxine-nonresponsive individuals with 339 patient-years of treatment were assessed using age-appropriate psychometric tests and were compared to those of 10 unaffected siblings (controls). Of the 23 individuals, 19 were diagnosed through newborn screening with early treatment, two were late-detected and two were untreated at the time of assessment. Thirteen of the newborn, screened group who were compliant with treatment had no complications, while the remaining 6, who had poor compliance, developed complications. Good compliance was defined by a lifetime plasma free homocystine median < 11 micromol/L. The newborn screened, good compliance group (n = 13) with a mean age of 14.4 years (range 4.4-24.9) had mean full-scale IQ (FIQ) of 105.8 (range 84-120), while the poorly compliant group (n = 6) with a mean age of 19.9 years (range 13.8-25.5) had a mean FIQ of 80.8 (range 40-103). The control group (n = 10) with mean age of 19.4 years (range 9.7-32.9) years had a mean FIQ of 102 (range 76-116). The two late-detected patients aged 18.9 and 18.8 years had FIQ of 80 and 102, while the two untreated patients aged 22.4 and 11.7 years had FIQ of 52 and 53, respectively. There was no statistical evidence of significant differences between the compliant, early-treated individuals and their unaffected siblings (controls) except for the FIQ, which was significantly higher than that of the unaffected siblings (p = 0.0397). These data, despite the relatively small numbers, suggest that early treatment with good biochemical control (lifetime plasma free homocystine median < 11 micromol/L) seems to prevent mental retardation.

Ocular findings among patients with late-diagnosed or poorly controlled homocystinuria compared with a screened, well-controlled population.

INTRODUCTION: Untreated homocystinuria (HCU) leads to systemic and ocular complications preventable by early treatment. METHODS: This study describes the ocular features in HCU patients who had late diagnosis or were noncompliant with treatment compared with a control group of early-diagnosed and well-controlled subjects. RESULTS: Fourteen late-diagnosed HCU patients with a median age at diagnosis of 4 years (range, 1.25-28 years) were studied. Five patients were born outside of Ireland or before screening began. All 14 patients had lens subluxation or dislocation at diagnosis. Only 28.6% of eyes had 20/40 vision or better. Three patients were tested for HCU following the diagnosis in a sibling. Four patients attended ophthalmology departments for a median of 12.8 years (range, 4-23 years) prior to diagnosis of HCU; all had steadily progressive myopic astigmatism and lens subluxation. Six patients who became poorly controlled in their teens or early twenties showed significant progression of their myopia, and 3 had phacodonesis or lens subluxation develop. All eyes in this group had 20/40 vision or better. Fifteen patients who were detected in the newborn period and remained well controlled had no evidence of lens subluxation. All of the control group patients had 20/20 vision bilaterally. The difference in visual acuity between late-diagnosed patients and the control group was highly significant (P =.0002). The differences in refractive errors between the groups were also highly significant (P =.0001). CONCLUSIONS: Lens subluxation is a principal feature of untreated HCU, yet we found a median lag period of 5.5 years in 4 cases before diagnosis. Young persons with marked and progressive myopia or idiopathic lens subluxation should be screened for HCU.

Rapid detection of the R408W and I65T mutations in phenylketonuria by glycosylase mediated polymorphism detection.

Mutation detection methods based upon chemical or enzymatic cleavage of DNA offer excellent detection efficiencies coupled with high throughput and low unit cost. We describe the application of the novel technique of Glycosylase Mediated Polymorphism Detection (GMPD) to the detection of two of the most common mutations of the PAH gene in the Irish population that cause phenylketonuria (PKU), R408W and I65T, which occur at relative frequencies of 41.0% and 10.4% respectively. GMPD assays for R408W and I65T were developed permitting fluorescent detection of cleavage products on the ALFexpresstrade mark automated DNA sequencer. The method was validated by screening a panel of PKU patients whose mutant genotypes had previously been characterised by standard methods. It also proved possible to perform multiplex detection of the two mutations by co-electrophoresis of GMPD products. GMPD is a rapid and robust method for the detection of the R408W and I65T mutations, whose key advantage lies in its use of a pair of enzymes with high cleavage efficiency to detect a number of mutations as compared to the use of individual digestions with a range of specific restriction endonuclease enzymes. Hum Mutat 17:432, 2001.

Ocular findings in glutaric aciduria type 1.

PURPOSE: To determine the nature and course of ocular abnormalities in glutaric aciduria (acidemia) type 1 (GA1). METHODS: Fifteen children with GA1 have been studied in the Republic of Ireland. A retrospective review of the records of the 6 children who died during their illness and prospective clinical examination of 9 survivors were performed. RESULTS: Seven of the 15 children had abnormal eye findings. Ocular complications included intraretinal hemorrhages, cataract, gaze palsy, strabismus, ametropia, and pigmentary retinopathy. CONCLUSION: Ocular involvement is common in glutaric aciduria. Complete ophthalmologic evaluation is recommended in all patients suspected to have this rare disease. Intraretinal hemorrhages due to GA1 could be misinterpreted as resulting from child abuse, and it is important to include this disorder with the differential diagnosis of child abuse.

Vascular complications of severe hyperhomocysteinemia in patients with homocystinuria due to cystathionine beta-synthase deficiency: effects of homocysteine-lowering therapy.

Homocystinuria (HCU) due to cystathionine beta-synthase (CBS) deficiency leads to severe hyperhomocysteinemia (HHcy). Vascular events (VE) remain the major cause of morbidity and mortality in the untreated patients with HCU. The study on the natural history of untreated HCU disclosed that, at the time of maximal risk, in other words beyond 10 years old, there was one event per 25 years. Recent studies from Australia (n = 32), The Netherlands (n = 28), and Ireland (n = 24) have documented the effects of long-term treatment on the vascular outcome of a total of 84 patients with 1314 patient-years of treatment for HCU. The mean (range) age was 27.8 (2.5 to 70) years. Five VE were recorded during treatment; one pulmonary embolism, two myocardial infarctions, and two abdominal aneurysms. All five VE occurred in B6-responsive patients at a mean (range) age of 48.8 (30 to 60) years. In 1314 patient-years of treatment, 53 VE would have been expected if they remained untreated; instead only 5 were documented, relative risk = 0.091 (95% confidence interval [CI] 0.043 to 0.190; p < 0.001). Appropriate homocysteine-lowering therapy for severe HHcy significantly reduced the vascular risk in patients with HCU. VE were rare with treatment despite the fact that the post-treatment homocysteine levels were several times higher than the cutoff point for homocysteine in the normal population. The present findings may have relevance to the current concept of "mild HHcy" as a risk factor for vascular disease, with elevated plasma homocysteine levels considerably lower than that of the post-treatment levels in this group of reported patients.

Prevention of cerebral palsy in glutaric aciduria type 1 by dietary management.

AIMS: To study retrospectively the effects of treatment and the clinical outcome in 12 patients with glutaric aciduria type 1; and to compare the outcome in 6 patients diagnosed as a result of family screening with 6 patients who were diagnosed late after symptomatic presentation. SETTING: The National Centre for Inherited Metabolic Disorders, The Children's Hospital, Dublin, Ireland. RESULT: Four of the 6 children detected on screening are developmentally normal, 1 died, and the remaining 1 has mild mental handicap. All 6 of the late diagnosed symptomatic group suffered dyskinetic cerebral palsy and 5 have died. CONCLUSION: Experience of 50 patient treatment years has shown that early intensive management can alter the natural history of this rare disorder.

Genetic basis of transferase-deficient galactosaemia in Ireland and the population history of the Irish Travellers.

Transferase-deficient galactosaemia, resulting from deficient activity of galactose-1-phosphate uridyltransferase (GALT), is relatively common among the Travellers, an endogamous group of commercial/industrial nomads within the Irish population. This study has estimated the incidence of classical transferase-deficient galactosaemia in Ireland and determined the underlying GALT mutation spectrum in the Irish population and in the Traveller group. Based upon a survey of newborn screening records, the incidence of classical transferase-deficient galactosaemia was estimated to be 1 in 480 and 1 in 30,000 among the Traveller and non-Traveller communities respectively. Fifty-six classical galactosaemic patients were screened for mutation in the GALT locus by standard molecular methods. Q188R was the sole mutant allele among the Travellers and the majority mutant allele among the non-Travellers (89.1%). Of the five non-Q188R mutant alleles in the non-Traveller group, one was R333G and one F194L with three remaining uncharacterized. Anonymous population screening has shown the Q188R carrier frequency to be 0.092 or 1 in 11 among the Travellers as compared with 0.009 or 1 in 107 among the non-Travellers. The Q188R mutation was shown to be in linkage disequilibrium with a Sac I RFLP flanking exon 6 of the GALT gene. This represents the first molecular genetic description of classical transferase-deficient galactosaemia in Ireland and raises intriguing questions concerning the genetic history of the Irish Travellers.

Factor V Leiden (Arg506Gln), a confounding genetic risk factor but not mandatory for the occurrence of venous thromboembolism in homozygotes and obligate heterozygotes for cystathionine beta-synthase deficiency.

Thrombosis is the major cause of morbidity and mortality in individuals with untreated classical homocystinuria (HCU) due to cystathionine beta-synthase deficiency and characterised by severe hyperhomocysteinaemia. In addition, mild and moderate hyperhomocysteinaemia and Factor V Leiden (FVL; Arg506Gln) have recently been identified as thrombotic risk factors. FVL. which renders resistance to activated Protein C, is the most common inherited genetic risk factor for thrombosis with a high allelic frequency amongst Caucasians. As thrombophilia is a multigenic disorder, 26 individuals with HCU (median age 17.6 years, range 3.5-32.8 years) and 36 obligate heterozygotes (median age 51.5 years, range 34-74 years) were screened for FVL. All the HCU individuals received treatment, except one, within 6 weeks of birth for those who were diagnosed at birth through the national newborn screening programme (n = 20) and at the time of diagnosis for those late detected (n = 5, mean age of starting treatment 4.9 years, range 1.4-11 years). All had been free from venous thrombosis, except one HCU individual and one HCU obligate heterozygote. Neither of the two individuals with venous thrombosis carried FVL. Two independent individuals with HCU (male 14.8 years; female 18.2 years) were heterozygous for FVL (allelic frequency 3.8%) and three independent HCU obligate heterozygotes (males 40 and 45.8 years; female 45.6 years) were also heterozygous for FVL (allelic frequency 4.16%). The findings in this small group suggest that FVL is not a mandatory but a significant confounding risk factor for the occurrence of thrombosis in HCU individuals and additional contributing factors may be required for thrombosis to occur in HCU obligate heterozygotes with FVL heterozygosity. Our data also suggest that treatment of HCU not only reduces the thrombotic risk in patients with isolated HCU but also in those with the additional FVL heterozygosity.

Homocystinuria due to cystathionine beta-synthase deficiency in Ireland: 25 years' experience of a newborn screened and treated population with reference to clinical outcome and biochemical control.

Homocystinuria (HCU) due to cystathionine beta-synthase deficiency (Mudd et al 1964) was independently described by Gerritsen and colleagues (USA) and Carson and colleagues (Northern Ireland) in 1962. The worldwide frequency of HCU has been reported as 1 in 344,000, while that in Ireland is much higher at 1 in 65,000, based on newborn screening and cases detected clinically. The national newborn screening programme for HCU in Ireland was started in 1971 using the bacterial inhibition assay. A total of 1.58 million newborn infants have been screened over a 25-year period up to 1996. Twenty-five HCU cases were diagnosed, 21 of whom were identified on screening. The remaining four HCU cases were missed and presented clinically; three of these were breast-fed and one was pyridoxine responsive. Twenty-four HCU cases were pyridoxine nonresponsive. Once the status of pyridoxine responsiveness was identified, all pyridoxine nonresponsive cases, but one, were started on a low methionine, cystine-enhanced diet supplemented with pyridoxine, vitamin B12 and folate. Dietary treatment commenced within 6 weeks of birth (range 8-42 days) for those cases detected by screening, while for the late-detected cases treatment was started upon presentation and diagnosis. Biochemical control was monitored measuring deproteinized plasma methionine, free homocystine and cystine at least once a month. Review of the clinical outcome of the 25 HCU cases with 365.7 patient-years of treatment revealed no HCU-related complications in 18 screened, dietary-treated cases. Fifteen of these had lifetime medians of free homocystine < or = 11 mumol/L (range 4-11). The remaining three cases with higher lifetime medians of free homocystine (18, 18 and 48 mumol/L) have developed increasing myopia recently. Among the three screened non-dietary-compliant cases, two have ectopia lentis, one has osteoporosis and two have mental handicap. Of the four cases missed on screening, three presented with ectopia lentis after the age of 2 years. There were no thromboembolic events in any of the 25 HCU cases. The lifetime medians for methionine ranged from 47 to 134 mumol/L. The Irish HCU clinical outcome data suggest that newborn screening, early commencement of dietary treatment and a lifetime median of free homocystine of < or = 11 mumol/L had significantly reduced the probability of developing complications when it was compared to the untreated HCU data (Mudd et al 1985).

Newborn screening for homocystinuria: Irish and world experience.

Newborn screening for cystathionine beta-synthase deficiency (homocystinuria; HCU) was started in the late 1960s using a bacterial inhibition assay (BIA). At least seven countries have either national or regional screening programmes; 12 programmes are known to have discontinued. The worldwide incidence of HCU is approximately 1 in 335,000 but varies from 1:65,000 (Ireland) to 1:900,000 (Japan). Methodologies include the BIA, one-dimensional or thin-layer amino acid chromatography and, more recently, tandem mass spectrometry. The BIA diagnostic cut off concentration of blood methionine varies from 67 to 270 micromol/ (10-40 mg/l) with a median of 135 micromol/l (20 mg/l). In Ireland, 25 cases of HCU from 19 families have been identified from 1.58 million newborn infants since 1971; 21 cases were detected through the screening programme. Of the four missed cases, three were breast-fed at the time of blood collection and one was pyridoxine responsive. These findings were in broad agreement with the results from five other programmes, in which approximately one in every five cases was missed by the screening programme. Early hospital discharge, low protein intake, high blood methionine cut-off concentration and pyridoxine responsiveness were all identified as contributing to missed cases.