Compound heterozygous variants in NBAS as a cause of atypical osteogenesis imperfecta.

BACKGROUND: Osteogenesis imperfecta (OI), the commonest inherited bone fragility disorder, affects 1 in 15,000 live births resulting in frequent fractures and reduced mobility, with significant impact on quality of life. Early diagnosis is important, as therapeutic advances can lead to improved clinical outcome and patient benefit. REPORT: Whole exome sequencing in patients with OI identified, in two patients with a multi-system phenotype, compound heterozygous variants in NBAS (neuroblastoma amplified sequence). Patient 1: NBAS c.5741G>A p.(Arg1914His); c.3010C>T p.(Arg1004*) in a 10-year old boy with significant short stature, bone fragility requiring treatment with bisphosphonates, developmental delay and immunodeficiency. Patient 2: NBAS c.5741G>A p.(Arg1914His); c.2032C>T p.(Gln678*) in a 5-year old boy with similar presenting features, bone fragility, mild developmental delay, abnormal liver function tests and immunodeficiency. DISCUSSION: Homozygous missense NBAS variants cause SOPH syndrome (short stature; optic atrophy; Pelger-Huet anomaly), the same missense variant was found in our patients on one allele and a nonsense variant in the other allele. Recent literature suggests a multi-system phenotype. In this study, patient fibroblasts have shown reduced collagen expression, compared to control cells and RNAseq studies, in bone cells show that NBAS is expressed in osteoblasts and osteocytes of rodents and primates. These findings provide proof-of-concept that NBAS mutations have mechanistic effects in bone, and that NBAS variants are a novel cause of bone fragility, which is distinguishable from 'Classical' OI. CONCLUSIONS: Here we report on variants in NBAS, as a cause of bone fragility in humans, and expand the phenotypic spectrum associated with NBAS. We explore the mechanism underlying NBAS and the striking skeletal phenotype in our patients.

A combined vascular surgical and clinical genetics approach to diffuse aneurysmal disease.

We report two patients who presented with extensive aneurysmal disease, in association with minimal external physical signs. Patient 1 remained genetically undiagnosed despite multiple structural, biochemical and genetic investigations. He made a good recovery following surgery for popliteal and left axillary artery aneurysms. Patient 2 was diagnosed with vascular type Ehlers-Danlos syndrome, associated with a high degree of tissue and blood vessel fragility, and is being managed conservatively. Early multidisciplinary assessment of such patients facilitates accurate diagnosis and management.

Palmoplantar contractures in childhood: a rare complication of vascular Ehlers-Danlos syndrome.

Although catastrophic vascular complications in vascular Ehlers-Danlos Syndrome (EDS) are well recognized, other complications such as flexion contractures and tendon nodules are rarely reported and poorly characterized. We report a young man with vascular EDS, who developed flexion contractures and tendon nodules, causing considerable disability. Limited management strategies are available for these complications, which have continued to prove a challenge to management.

Identification of a novel heterozygous mutation in exon 50 of the COL1A1 gene causing osteogenesis imperfecta.

UNLABELLED: A 19-year-old woman was diagnosed with osteogenesis imperfecta (OI). She had sustained numerous low-trauma fractures throughout her childhood, including a recent pelvic fracture (superior and inferior ramus) following a low-impact fall. She had the classical blue sclerae, and dual energy X-ray absorptiometry (DEXA) bone scanning confirmed low bone mass for her age in the lumbar spine (Z-score was -2.6). However, despite these classical clinical features, the diagnosis of OI had not been entertained throughout the whole of her childhood. Sequencing of her genomic DNA revealed that she was heterozygous for the c.3880_3883dup mutation in exon 50 of the COL1A1 gene. This mutation is predicted to result in a frameshift at p.Thr1295, and truncating stop codon 3 amino acids downstream. To our knowledge, this mutation has not previously been reported in OI. LEARNING POINTS: OI is a rare but important genetic metabolic bone and connective tissue disorder that manifests a diverse clinical phenotype that includes recurrent low-impact fractures.Most mutations that underlie OI occur within exon 50 of the COL1A1 gene (coding for protein constituents of type 1 pro-collagen).The diagnosis of OI is easily missed in its mild form. Early diagnosis is important, and there is a need for improved awareness of OI among health care professionals.OI is a diagnosis of exclusion, although the key diagnostic criterion is through genetic testing for mutations within the COL1A1 gene.Effective management of OI should be instituted through a multidisciplinary team approach that includes a bone specialist (usually an endocrinologist or rheumatologist), a geneticist, an audiometrist and a genetic counsellor. Physiotherapy and orthopaedic surgery may also be required.

Commentary: What degree of hyperphenylalaninaemia requires treatment?

Despite some 50 years' experience in the treatment of phenylketonuria and numerous scientific publications on the subject there is no clear consensus as to what degree of hyperphenylalaninaemia will result in intellectual impairment. Studies of three main types, on untreated cases of moderate hyperphenylalaninaemia, on treated cases of phenylketonuria, and on the effects of current blood phenylalanine concentration on executive function, have lead to different conclusions. Overall, there appears to be a fairly strong case for limiting dietary treatment to individuals whose blood phenylalanine levels would otherwise exceed 600 µmol/L. This is now policy in some European countries but a formal large-scale study of long-term outcomes to validate the approach is urgently required.

Femoral artery dissection in vascular type Ehlers-Danlos syndrome; leave well alone?

Vascular Ehlers-Danlos Syndrome (EDS) is a rare autosomal dominant condition resulting from a defect in type III procollagen synthesis. This causes the development of severe vascular pathologies, including arterial rupture and pseudoaneurysm formation. We present a case of a young boy previously diagnosed with vascular EDS due to a Gly975Val substitution in the collagen α1(III) chain presenting with a common femoral artery dissection secondary to minimal trauma. This was managed conservatively with serial duplex scans and gentle mobilization. At follow up the patient had returned to normal activities, with MRA and duplex scans showing complete resolution of the dissection.

Newborn blood spot screening: new opportunities, old problems.

Newborn screening is evolving very rapidly. Geographical coverage is expanding, particularly for common disorders such as congenital hypothyroidism. New technologies, particularly tandem mass spectrometry and high throughput mutation analysis, have increased greatly the range of disorders which could be covered. However, these new possibilities are being exploiting at very different rates in different countries. This is due in part to the different ways in which generally-accepted screening criteria, based on the ten principles of Wilson and Jungner, are being interpreted and applied to policy. The appropriate management of some of the conditions newly-detectable by screening also remains controversial and there is a pressing need to align screening policy and clinical practice. Critical analysis and careful collection of data on an international basis are required to resolve these issues.

Qualitative urinary organic acid analysis: methodological approaches and performance.

A programme for proficiency testing of biochemical genetics laboratories undertaking urinary qualitative organic acid analysis and its results for 50 samples examined for factors contributing to poor performance are described. Urine samples from patients in whom inherited metabolic disorders have been confirmed as well as control urines were circulated to participants and the results from 94 laboratories were evaluated. Laboratories showed variability both in terms of their individual performance and on a disease-specific basis. In general, conditions including methylmalonic aciduria, propionic aciduria, isovaleric aciduria, mevalonic aciduria, Canavan disease and 3-methylcrotonyl-CoA carboxylase were readily identified. Detection was poorer for other diseases such as glutaric aciduria type II, glyceric aciduria and, in one sample, 3-methylcrotonyl-CoA carboxylase deficiency. To identify the factors that allow some laboratories to perform well on a consistent basis while others perform badly, we devised a questionnaire and compared the responses with the results for performance in the scheme. A trend towards better performance could be demonstrated for those laboratories that regularly use internal quality control (QC) samples in their sample preparation (p = 0.079) and those that participate in further external quality assurance (EQA) schemes (p = 0,040). Clinicians who depend upon these diagnostic services to identify patients with these defects and the laboratories that provide them should be aware of the potential for missed diagnoses and the factors that may lead to improved performance.

Cumulative life course and adult socioeconomic status and markers of inflammation in adulthood.

OBJECTIVE: To examine the association between cumulative life course and adult socioeconomic status (SES) and adult levels of inflammatory risk markers (fibrinogen, white blood cell count (WBC), C-reactive protein (CRP), von Willebrand factor (vWF) and an overall inflammatory score). DESIGN: Retrospective cohort study. SETTING: 12,681 white and African-American participants in the Atherosclerosis Risk in Communities (ARIC) study and two ancillary studies. METHODS: Participants provided information on SES and place of residence in childhood and young (30-40 years) and mature (45+) adulthood. Residences were linked to census data for neighbourhood SES information. Multiple imputation (MI) was used for missing data. Linear regression and adjusted geometric means were used to estimate the effects of SES on inflammatory risk marker levels. RESULTS: Graded, statistically significant associations were observed between greater cumulative life-course exposure to low education and social class and elevated levels of fibrinogen and WBC among white participants. Stronger graded, statistically significant associations were observed between low adult education, social class and neighbourhood SES and elevated inflammatory levels. Associations were weaker and less consistent in African-Americans. Covariate adjustment attenuated results but many associations remained strong. CONCLUSIONS: Our results suggest that cumulative exposure to adverse SES conditions across the life course and low adult SES are associated with an elevated systemic inflammatory burden in adulthood. Chronic systemic inflammation may be one pathway linking low life-course SES and elevated cardiovascular disease risk.

Introducing new screens: why are we all doing different things?

The disease panels covered by newborn blood spot screening vary greatly from country to country. There are different interpretations of the Wilson and Jungner principles and of underlying data in the scientific literature, and great disparities between the value judgements applied in screening and in routine clinical practice.

Population quantile-quantile plots for monitoring assay performance in newborn screening.

Immunoreactive trypsinogen (IRT) used in screening for cystic fibrosis is heterogeneous, poorly characterized, and displays marked matrix effects when incorporated into blood spots, making long-term control of assay calibration difficult. The cut-off required to select a fixed proportion of samples (0.5% for the UK protocol) for second-tier mutation analysis varies over time, partly owing to slight differences in calibration of individual lots of assay kit. To investigate this and possible inter-laboratory differences in analytical performance, we developed a monitoring system based on the distribution of measured IRT concentrations in the screened samples. Results were collected fortnightly from five UK screening laboratories in the form of numbers of samples in histogram 'bins' of IRT concentration. These data were converted to cumulative percentages and the IRT concentrations at fixed centiles then approximated by triangulation. The quantile-quantile plot of any subset (by laboratory or by kit lot) of these data using pooled results (all-laboratories all-kit-lots, approximately 270,000 samples) as the reference distribution is analogous to a calibration curve and gives a measure of bias in terms of sensitivity (slope) and baseline (y-intercept). This allows a revised 99.5th centile cut-off for each subset to be calculated directly. A similar approach has allowed inter-laboratory comparison of tandem-mass spectrometric assays for free carnitine (with emphasis on low values) and phenylalanine and has demonstrated that apparently trivial differences in instrumentation and procedures have resulted in marked variation in resultant assay performance.

International perspectives on newborn screening.

The development of electrospray tandem mass spectrometry (MS-MS) has greatly increased the number of diseases that can be detected by newborn blood-spot screening. Different countries are introducing the technology at different rates and for different disease panels. Current policies in the United Kingdom, Germany and the United States are taken as examples. In the United Kingdom, many laboratories are using MS-MS for routine screening for phenylketonuria but, except for those participating in a two-year pilot study of screening for medium-chain acyl-CoA dehydrogenase deficiency, are forbidden use MS-MS to screen for other disorders. In Germany there has been considerable experience of MS-MS screening for a wide range of diseases, but recently the Federal Ministry for Health and Social Security prescribed a much more restricted disease panel, with the instruction that any other diagnostic results are to be suppressed and not reported. By contrast, a recent report from the American College of Medical Genetics, still being debated, recommends screening procedures that will detect an extremely broad range of disorders, including some that are very rare or of unproven clinical significance. The lack of even broad concordance at the level of national policy is extremely disturbing. Though all discussion is nominally founded on the ten principles laid down by Wilson and Jungner in 1968, there seems no generally accepted way of using these principles, or derived criteria, as objective decision tools. Alternative, less categorical, approaches are needed: the disorders concerned are not homogeneous entities and there may be advantages to screening other than reducing morbidity or mortality.

Mutation and biochemical analysis in carnitine palmitoyltransferase type II (CPT II) deficiency.

Carnitine palmitoyltransferase type II (CPT II) deficiency has three basic phenotypes, late-onset muscular (mild), infantile/juvenile hepatic (intermediate) and severe neonatal. We have measured fatty acid oxidation and CPT II activity and performed mutation studies in 24 symptomatic patients representing the full clinical spectrum of disease. Severe and intermediate phenotypes show a clear correlation with biochemical indices and genetic analysis revealed causative mutations in most patients. Studies of mild phenotypes suggest a more complex interaction, with higher residual fatty acid oxidation, a wider range of CPT II activity (10-60%) but little evidence of genotype-phenotype correlation. Residual CPT II mutant protein from myopathic patients shows thermal instability at 41 degrees C. The common 'polymorphisms' V3681 and M647V are strikingly overrepresented in the myopathic patients, the implication being that they may significantly influence the manifestation of clinical disease and could therefore potentially be considered as a susceptibility variants. Among myopathic individuals, males comprised 88% of patients, suggesting increased susceptibility to clinical disease. A small number of symptomatic patients appear to have significant residual CPT II activity (42-60%) The synergistic interaction of partial deficiencies of CPT II, muscle adenosine monophosphate deaminase and possibly other enzymes of muscle energy metabolism in the aetiology of episodic myopathy deserves wider consideration.

In utero exposure to lead and cord blood total IgE. Is there a connection?

BACKGROUND: Lead exposure and total immunoglobulin E (IgE) have been shown to be positively related in animals and humans even at lead levels below those recognized as toxic. In the last decades, exposure to lead has become more frequent in urban areas of industrialized as well as of developing countries where IgE-mediated allergy prevalence has also increased. METHODS: We examined for the first time the relationship between in utero exposure to lead and cord blood total IgE in two samples of 137 and 237 mother-newborn pairs, respectively, recruited in Paris. RESULTS: Cord blood IgE was positively related to hair lead level at birth, providing an integrated measure of long-term exposure in utero, in each cohort (Spearman's coefficient r = 0.32, P < 0.001 and r = 0.19, P < 0.01, respectively) and in the combined cohort (r = 0.21; P < 0.01). The relationship appeared to be more pronounced in newborns of nonallergic mothers (r = 0.24; P < 0.01) than in those of allergic mothers (r = 0.12). This could be due to the fact that familial history of allergy, the strongest determinant of IgE development, may overshadow the influence of lead on IgE in the offspring. CONCLUSIONS: Our findings suggest a possible intervention of environmental exposure besides genetic factors in early life development of IgE production. Further studies are needed to confirm the finding.

2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency in a 23-year-old man.

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase (EC 1.1.1.178) deficiency is a recently described defect of isoleucine catabolism. The disorder is characterized by normal early development followed by a progressive loss of mental and motor skills. Deterioration may be rapid or may follow a slower decline with a possible stabilization of the disorder on a low-protein diet and appropriate medication. We report a 23-year-old man with 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency with a very mild clinical course. He had apparently normal early development and remained relatively well until the age of 6 years, when he contracted measles. Following this illness, his motor skills and school progress deteriorated. At 15 years he had significant dysarthria, and generalized rigidity with some dystonic and unusual posturing. He was then treated with a low-protein high-carbohydrate diet with a good response in terms of balance and gait. At 18 years he was given benzhexol (Artane), increased slowly from 2 mg to 6 mg daily, resulting in improvement in tremor and dystonia. At 23 years he can dress himself and works in sheltered employment but remains severely dysarthric.

Newborn mass screening versus selective investigation: benefits and costs.

Cost-benefit analysis of newborn screening has an unimpressive record and yet it is still regarded as an important decision tool. This workshop surveyed ongoing research into the costs and benefits of systematic whole-population screening, as opposed to selective investigation of symptomatic patients, for inherited metabolic disease. Much current interest is focused on newborn screening by tandem mass spectrometry, which can replace current methods for detecting phenylketonuria and cover a much wider range of diseases. Two observational studies are comparing cost-effectiveness of tandem mass spectrometry screening versus symptomatic diagnosis in either concurrent or historical control populations. A number of other studies are assessing screening performance against predetermined criteria but without any formal control group. Medium-chain acyl-CoA dehydrogenase deficiency is the most common of the additional diseases being detected and it seems that octanoylcarnitine in blood is a particularly sensitive indicator: some of the cases detected by screening have genotypes suggesting a relatively low risk of serious metabolic decompensation. Ongoing studies should provide further quantitative and qualitative data but will not in themselves define the optimum balance between screening sensitivity and specificity.

Features of carnitine palmitoyltransferase type I deficiency.

Carnitine palmitoyltransferase type I (CPT I) is unique among long-chain fatty acid oxidation enzymes in that there are two tissue-specific isoforms, 'hepatic' and 'muscle', which are encoded by two separate genes. The 'hepatic' isoform is expressed in liver, kidney and fibroblasts and at low levels in the heart, while the other isoform occurs in skeletal muscle and is the predominant form in heart. Reported patients with CPT I deficiency lack activity of the hepatic isoform and present before 30 months of age with hypoketotic hypoglycaemia, hepatomegaly with raised transaminases, seizures and coma. We discuss four new cases in three families showing, variously, renal tubular acidosis, transient hyperlipidaemia and, paradoxically, myopathy with elevated creatinine kinase or cardiac involvement in the neonatal period as additional features that deserve wider recognition.