Julian P Hamilton-Shield

Mutations in NLRP5 are associated with reproductive wastage and multilocus imprinting disorders in humans

Human-imprinting disorders are congenital disorders of growth, development and metabolism, associated with disturbance of parent of origin-specific DNA methylation at imprinted loci across the genome. Some imprinting disorders have higher than expected prevalence of monozygotic twinning, of assisted reproductive technology among parents, and of disturbance of multiple imprinted loci, for which few causative trans-acting mutations have been found. Here we report mutations in NLRP5 in five mothers of individuals affected by multilocus imprinting disturbance. Maternal-effect mutations of other human NLRP genes, NLRP7 and NLRP2, cause familial biparental hydatidiform mole and multilocus imprinting disturbance, respectively. Offspring of mothers with NLRP5 mutations have heterogenous clinical and epigenetic features, but cases include a discordant monozygotic twin pair, individuals with idiopathic developmental delay and autism, and families affected by infertility and reproductive wastage. NLRP5 mutations suggest connections between maternal reproductive fitness, early zygotic development and genomic imprinting.

The HNF4A R76W mutation causes atypical dominant Fanconi syndrome in addition to a β cell phenotype

Background Mutation specific effects in monogenic disorders are rare. We describe atypical Fanconi syndrome caused by a specific heterozygous mutation in HNF4A. Heterozygous HNF4A mutations cause a beta cell phenotype of neonatal hyperinsulinism with macrosomia and young onset diabetes. Autosomal dominant idiopathic Fanconi syndrome (a renal proximal tubulopathy) is described but no genetic cause has been defined. Methods and Results We report six patients heterozygous for the p.R76W HNF4A mutation who have Fanconi syndrome and nephrocalcinosis in addition to neonatal hyperinsulinism and macrosomia. All six displayed a novel phenotype of proximal tubulopathy, characterised by generalised aminoaciduria, low molecular weight proteinuria, glycosuria, hyperphosphaturia and hypouricaemia, and additional features not seen in Fanconi syndrome: nephrocalcinosis, renal impairment, hypercalciuria with relative hypocalcaemia, and hypermagnesaemia. This was mutation specific, with the renal phenotype not being seen in patients with other HNF4A mutations. In silico modelling shows the R76 residue is directly involved in DNA binding and the R76W mutation reduces DNA binding affinity. The target(s) selectively affected by altered DNA binding of R76W that results in Fanconi syndrome is not known. Conclusions The HNF4A R76W mutation is an unusual example of a mutation specific phenotype, with autosomal dominant atypical Fanconi syndrome in addition to the established beta cell phenotype.

A double heterozygote for familial hypercholesterolaemia and familial defective apolipoprotein B-100

Autosomal dominant hypercholesterolaemia is genetically heterogeneous, but most commonly (∼93%) caused by mutations in low-density lipoprotein receptor (LDLR), where the disease is known as familial hypercholesterolaemia (FH), or apolipoprotein B-100 (APOB) (∼5.5%), where the disease is known as familial defective APOB (FDB), while in ∼2% of patients the mutation is in the proprotein convertase subtilisin/kexin type 9 gene. Homozygous FH having inheritance of two LDLR mutations is a rare but recognized syndrome associated with an extreme hypercholesterolaemia and early-onset coronary artery disease. We present a 15-year-old girl with untreated total cholesterol levels of 8.8 mmol/L who was heterozygous for both the LDLR p.Leu479Pro and APOB p.Arg3527Gln mutation. Cascade testing confirmed the paternal origin of the LDLR mutation and revealed a maternal diagnosis of FDB. This case provides further evidence that the combined effect of an LDLR and an APOB mutation give rise to a phenotype more severe than either mutation alone and is more severe than homozygous FDB, but less severe than homozygous FH. It also highlights the need to consider the presence of additional mutations in families where relatives have varying phenotypes.

Reduced beta‐cell reserve and pancreatic volume in survivors of childhood acute lymphoblastic leukaemia treated with bone marrow transplantation and total body irradiation

Impaired glucose tolerance (IGT) and diabetes mellitus (DM) occur more frequently after bone marrow transplantation and total body irradiation (BMT/TBI), but the mechanism is unclear. This study investigates insulin sensitivity, β‐cell reserve and pancreatic volume in adult survivors of childhood acute lymphoblastic leukaemia (ALL).

Polycystic kidney disease with hyperinsulinemic hypoglycemia caused by a promoter mutation in phosphomannomutase 2

Hyperinsulinemic hypoglycemia (HI) and congenital polycystic kidney disease (PKD) are rare, genetically heterogeneous disorders. The co-occurrence of these disorders (HIPKD) in 17 children from 11 unrelated families suggested an unrecognized genetic disorder. Whole-genome linkage analysis in five informative families identified a single significant locus on chromosome 16p13.2 (logarithm of odds score 6.5). Sequencing of the coding regions of all linked genes failed to identify biallelic mutations. Instead, we found in all patients a promoter mutation (c.-167G>T) in the phosphomannomutase 2 gene (PMM2), either homozygous or in trans with PMM2 coding mutations. PMM2 encodes a key enzyme in N-glycosylation. Abnormal glycosylation has been associated with PKD, and we found that deglycosylation in cultured pancreatic β cells altered insulin secretion. Recessive coding mutations in PMM2 cause congenital disorder of glycosylation type 1a (CDG1A), a devastating multisystem disorder with prominent neurologic involvement. Yet our patients did not exhibit the typical clinical or diagnostic features of CDG1A. In vitro, the PMM2 promoter mutation associated with decreased transcriptional activity in patient kidney cells and impaired binding of the transcription factor ZNF143. In silico analysis suggested an important role of ZNF143 for the formation of a chromatin loop including PMM2 We propose that the PMM2 promoter mutation alters tissue-specific chromatin loop formation, with consequent organ-specific deficiency of PMM2 leading to the restricted phenotype of HIPKD. Our findings extend the spectrum of genetic causes for both HI and PKD and provide insights into gene regulation and PMM2 pleiotropy.

The Measurement of Ammonia in Human Breath and its Potential in Clinical Diagnostics

ABSTRACT Ammonia is an important component of metabolism and is involved in many physiological processes. During normal physiology, levels of blood ammonia are between 11 and 50 µM. Elevated blood ammonia levels are associated with a variety of pathological conditions such as liver and kidney dysfunction, Reyes syndrome and a variety of inborn errors of metabolism including urea cycle disorders (UCD), organic acidaemias and hyperinsulinism/hyperammonaemia syndrome in which ammonia may reach levels in excess of 1 mM. It is highly neurotoxic and so effective measurement is critical for assessing and monitoring disease severity and treatment. Ammonia is also a potential biomarker in exercise physiology and studies of drug metabolism. Current ammonia testing is based on blood sampling, which is inconvenient and can be subject to significant analytical errors due to the quality of the sample draw, its handling and preparation for analysis. Blood ammonia is in gaseous equilibrium with the lungs. Recent research has demonstrated the potential use of breath ammonia as a non-invasive means of measuring systemic ammonia. This requires measurement of ammonia in real breath samples with associated temperature, humidity and gas characteristics at concentrations between 50 and several thousand parts per billion. This review explores the diagnostic applications of ammonia measurement and the impact that the move from blood to breath analysis could have on how these processes and diseases are studied and managed.

High birth weight in a suburban hospital in Cameroon: an analysis of the clinical cut-off, prevalence, predictors and adverse outcomes

Background and aims High birth weight (HBW) increases the risk of maternal and fetal morbidity and mortality. Its prevalence and adverse outcomes may be reduced if risk factors are identified and managed during pregnancy. The cut-off value for HBW remains debatable. The objectives of this study were to identify the optimal cut-off value and determine the prevalence, predictors and adverse outcomes of HBW in a suburban area of Cameroon. Design A 6-year retrospective register analysis and a 3-month prospective phase. Setting A secondary care level (regional) hospital in the city of Buea (southwest region of Cameroon). Participants Women who delivered in this hospital over a 6-year period (retrospective phase) and consenting pregnant mothers and their infants (singletons, born at >28 weeks gestation) (prospective phase). Outcome measures 90th centile of birth weights; prevalence of HBW defined as birth weight above the 90th centile; sociodemographic, maternal and obstetrical factors associated with HBW; maternal and neonatal adverse outcomes of HBW. Results Of the 4941 newborns reviewed in registers, the 90th centile of birth weights was 3850 g. Using this new cut-off, we obtained a prevalence of 14.0% for HBW in the 200 newborns included in the prospective phase. This was significantly higher than the prevalence (9.5%) yielded when the traditional cut-off of 4000 g was used (p=0.003). None of the factors assessed was independently associated with HBW. Newborns with HBW were more likely to have shoulder dystocia (p<0.01), and their mothers more likely to suffer from prolonged labour (p=0.01) and postpartum haemorrhage (p<0.01). Conclusions The results of this study suggest that the cut-off for HBW in this population should be 3850 g. Thus, 3 of every 10 babies born with HBW in this hospital are likely not receiving optimal postnatal care because 4000 g is currently used to qualify for additional support.

Overweight and obesity in children aged 3–13 years in urban Cameroon: a cross-sectional study of prevalence and association with socio-economic status

BackgroundChildhood overweight/obesity is increasing rapidly in developing countries. There is a need to provide more evidence on its burden in sub-Saharan Africa, and to identify associated factors in order to set preventive measures. We aimed to determine the prevalence of overweight/obesity and assess its association with the socioeconomic status in nursery and primary school children in urban Cameroon.MethodsIn this cross-sectional study, we included by multi-staged cluster random sampling 1343 children from high (HSES, n = 673) and low (LSES, n = 670) socioeconomic status schools in Douala. Parent/child demographic data were collected, and children’s anthropometric parameters were measured using validated methods. The World Health Organization body mass index-for-age reference curves were used.ResultsThe prevalence of overweight/obesity was 12.5% (13.2% in girls, 11.8% in boys). The risk of overweight/obesity was 2.40 (95% CI 1.70, 3.40) higher in HSES children compared to LSES after adjusting for age and gender. However this association was attenuated to 1.18 (95% CI 0.59, 2.35) once adjustment had been made for a range of potential confounders.ConclusionsOverweight/obesity is relatively common in sub-Saharan African children and prevalence is associated with HSES. However, this association may be mediated by sweet drink consumption, passive means of travel to school and not doing sport at school. We suggest that these potentially modifiable behaviors may be effective targets for obesity prevention. Further studies should specifically focus on unhealthy behaviors that mediate overweight/obesity as well as other non communicable diseases in children.

Maternal variants in NLRP and other maternal effect proteins are associated with multilocus imprinting disturbance in offspring

Background Genomic imprinting results from the resistance of germline epigenetic marks to reprogramming in the early embryo for a small number of mammalian genes. Genetic, epigenetic or environmental insults that prevent imprints from evading reprogramming may result in imprinting disorders, which impact growth, development, behaviour and metabolism. We aimed to identify genetic defects causing imprinting disorders by whole-exome sequencing in families with one or more members affected by multilocus imprinting disturbance. Methods Whole-exome sequencing was performed in 38 pedigrees where probands had multilocus imprinting disturbance, in five of whom maternal variants in NLRP5 have previously been found. Results We now report 15 further pedigrees in which offspring had disturbance of imprinting, while their mothers had rare, predicted-deleterious variants in maternal effect genes, including NLRP2, NLRP7 and PADI6. As well as clinical features of well-recognised imprinting disorders, some offspring had additional features including developmental delay, behavioural problems and discordant monozygotic twinning, while some mothers had reproductive problems including pregnancy loss. Conclusion The identification of 20 putative maternal effect variants in 38 families affected by multilocus imprinting disorders adds to the evidence that maternal genetic factors affect oocyte fitness and thus offspring development. Testing for maternal-effect genetic variants should be considered in families affected by atypical imprinting disorders.

Obesity in adolescents with chronic fatigue syndrome: an observational study.

Objective Identify the prevalence of obesity in patients with chronic fatigue syndrome (CFS) compared with healthy adolescents, and those identified with CFS in a population cohort. Design Cross-sectional analysis of multiple imputed data. Setting Data from UK paediatric CFS/myalgic encephalomyelitis (CFS/ME) services compared with data collected at two time points in the Avon Longitudinal Study of Parents and Children (ALSPAC). Patients 1685 adolescents who attended a CFS/ME specialist service between 2004 and 2014 and 13 978 adolescents aged approximately 13 years and 16 years participating in the ALSPAC study. Main outcome measures Body mass index (BMI) (kg/m2), sex-specific and age-specific BMI Z-scores (relative to the International Obesity Task Force cut-offs) and prevalence of obesity (%). Results Adolescents who had attended specialist CFS/ME services had a higher prevalence of obesity (age 13 years: 9.28%; age 16 years: 16.43%) compared with both adolescents classified as CFS/ME in ALSPAC (age 13 years: 3.72%; age 16 years: 5.46%) and those non-CFS in ALSPAC (age 13 years: 4.18%; age 16 years: 4.46%). The increased odds of obesity in those who attended specialist services (relative to non-CFS in ALSPAC) was apparent at both 13 years (OR: 2.31 (1.54 to 3.48)) and 16 years, with a greater likelihood observed at 16 years (OR: 4.07 (2.04 to 8.11)). Conclusions We observed an increased prevalence of obesity in adolescents who were affected severely enough to be referred to a specialist CFS/ME service. Further longitudinal research is required in order to identify the temporal relationship between the two conditions.