Isodisomy of chromosome 6 in a newborn with methylmalonic acidemia and agenesis of pancreatic beta cells causing diabetes mellitus

Metabolic pathways at the crossroads of diabetes and inborn errors

Research over the past two decades has led to advances in our understanding of the genetic and metabolic factors that underlie the pathogenesis of type 2 diabetes mellitus (T2DM). While T2DM is defined by its hallmark metabolic symptoms, the genetic risk factors for T2DM are more immune-related than metabolism-related, and the observed metabolic disease may be secondary to chronic inflammation. Regardless, these metabolic changes are not benign, as the accumulation of some metabolic intermediates serves to further drive the inflammation and cell stress, eventually leading to insulin resistance and ultimately to T2DM. Because many of the biochemical changes observed in the pre-diabetic state (i.e., ectopic lipid storage, increased acylcarnitines, increased branched-chain amino acids) are also observed in patients with rare inborn errors of fatty acid and amino acid metabolism, an interesting question is raised regarding whether isolated metabolic gene defects can confer an increased risk for T2DM. In this review, we attempt to address this question by summarizing the literature regarding the metabolic pathways at the crossroads of diabetes and inborn errors of metabolism. Studies using cell culture and animal models have revealed that, within a given pathway, disrupting some genes can lead to insulin resistance while for others there may be no effect or even improved insulin sensitivity. This differential response to ablating a single metabolic gene appears to be dependent upon the specific metabolic intermediates that accumulate and whether these intermediates subsequently activate inflammatory pathways. This highlights the need for future studies to determine whether certain inborn errors may confer increased risk for diabetes as the patients age.

The Missing lnc(RNA) between the pancreatic β-cell and diabetes

Diabetes mellitus represents a group of complex metabolic diseases that result in impaired glucose homeostasis, which includes destruction of β-cells or the failure of these insulin-secreting cells to compensate for increased metabolic demand. Despite a strong interest in characterizing the transcriptome of the different human islet cell types to understand the molecular basis of diabetes, very little attention has been paid to the role of long non-coding RNAs (lncRNAs) and their contribution to this disease. Here we summarize the growing evidence for the potential role of these lncRNAs in β-cell function and dysregulation in diabetes, with a focus on imprinted genomic loci.

Maternal uniparental isodisomy causing autosomal recessive GM1 gangliosidosis: a clinical report

Uniparental disomy is a genetic cause of disease that may result in the inheritance of an autosomal recessive condition. A child with developmental delay and hypotonia was seen and found to have severely abnormal myelination. Lysosomal enzyme testing identified an isolated deficiency of beta-galactosidase. Subsequently, homozygous missense mutations in the galactosidase, beta 1 (GLB1) gene on chromosome 3 were found. Parental testing confirmed inheritance of two copies of the same mutated maternal GLB1 gene, and no paternal copy. SNP analysis was also done to confirm paternity. The patient was ultimately diagnosed with autosomal recessive GM1 gangliosidosis caused by maternal uniparental isodisomy. We provide a review of this patient and others in which uniparental disomy (UPD) of a non-imprinted chromosome unexpectedly caused an autosomal recessive condition. This is the first case of GM1 gangliosidosis reported in the literature to have been caused by UPD. It is important for genetic counselors and other health care providers to be aware of the possibility of autosomal recessive disease caused by UPD. UPD as a cause of autosomal recessive disease drastically changes the recurrence risk for families, and discussions surrounding UPD can be complex. Working with families to understand UPD when it occurs requires a secure and trusting counselor-family relationship.

Defect of cobalamin intracellular metabolism presenting as diabetic ketoacidosis: a rare manifestation

Hypoglycemia is the usual feature of commonly occurring organic acidemias. Organic acidemias manifesting as hyperglycemia or diabetic ketoacidosis are rare and only a few cases have been reported. We report a 13-month-old boy who presented with vomiting, dehydration, coma, hyperglycemia, high anion gap metabolic acidosis and ketosis, mimicking diabetic ketoacidosis (DKA). Treatment with parenteral fluid, electrolytes, and insulin infusion resulted in an improvement in hyperglycemia, but persistence of metabolic acidosis and lack of improvement of neurologic status led us to suspect an organic acidemia. Urinary organic acid analysis revealed increased methylmalonic acid levels. In addition, hyperhomocysteinemia and homocystinuria were also noted in presence of normal vitamin B12 levels. This confirmed the diagnosis of cobalamin metabolism defect leading to combined methylmalonic aciduria and homocystinuria. There was some improvement in neurologic status and metabolic parameters after treatment with low-protein diet, vitamin B12, folic acid, and L-carnitine, but he ultimately succumbed to polymicrobial nosocomial sepsis. The entire MMACHC gene of the patient was sequenced and no mutations were identified. This is probably the first case report of cobalamin intracellular metabolism defect (CblC/CblD/CblF/CblJ or ABCD4) presenting as diabetic ketoacidosis.

Overexpression of ZAC impairs glucose-stimulated insulin translation and secretion in clonal pancreatic beta-cells

BACKGROUND

ZAC (Zinc finger protein that regulates apoptosis and cell-cycle arrest) is a candidate gene for transient neonatal diabetes mellitus (TNDM). This condition involves severe insulin deficiency at birth that reverses over weeks or months but may relapse with diabetes recurring in later life. ZAC overexpression in transgenic mice has previously been shown to result in complex changes in both beta-cell mass and possibly function. The present study therefore aimed to examine the role of ZAC in beta-cell function in vitro, independent of the confounder of a reduced beta-cell mass at birth.

METHODS

Overexpression of ZAC was achieved through the tetracycline-regulatable system in the beta-cell line, INS-1.

RESULTS

We found that ZAC overexpression exerted no significant effect on proliferation in this transformed cell line at any of the glucose concentrations examined. By contrast, glucose-stimulated insulin secretion was impaired through a mechanism downstream of cytosolic Ca(2+) increases. Furthermore, glucose-stimulated proinsulin biosynthesis was inhibited despite an increase in insulin transcript level. Finally, we found that glucose downregulated ZAC expression in both INS-1 cells and primary mouse islets.

CONCLUSIONS

These results indicate that ZAC is a negative regulator of the acute stimulatory effects of glucose on beta-cells, and provide a possible explanation for both insulin deficiency in the neonate and the later relapse of diabetes in patients with transient neonatal diabetes mellitus cases.

Methylmalonic acidemia mimicking diabetic ketoacidosis in an infant

Methylmalonic acidemia (MMA) is an inherited organic acidemia usually present with recurrent episodes of acute illness. A typical episode is ushered in with ketonuria and vomiting, followed by acidosis, dehydration, and lethargy, leading, in the absence of aggressive treatment, to coma and death. We report an infant with MMA presented with diabetes symptoms. A 13-month-old girl complained of polydipsia, diuresis, and loss of weight. She had clinical signs of diabetic ketoacidosis such as dehydration, deep sighing respiration, smell of ketones, lethargy, and vomiting. Laboratory analysis showed hyperglycemia with acidosis and ketonuria. She was treated with parenteral fluid, electrolyte, and insulin infusion. Two days after her discharge, after having a meal rich in protein, she was brought unconscious with hepatomegaly, severe acidosis, ketonuria, and mild hyperammonemia. The absence of hyperglycemia and the presence of neurologic findings suggested organic acidemia. MMA was diagnosed because of methylmalonic aciduria and elevated C3 carnitine esters. Cranial magnetic resonance imaging (MRI) showed increased uptake of radiocontrast material in the basal ganglia bilaterally. A homozygous mutation in exon 4 of the MMAA gene was found in mutation analysis and confirmed the diagnosis of cblA-deficient MMA. Neurologic regression was improved with treatment of low-protein diet, vitamin B12, and l-carnitine. In patients born to consanguineous parents who admit during infancy with severe acidosis refractory to treatment, organic acidemias should be kept in mind, even they have high blood glucose. The definitive diagnosis is important because it may allow a specific treatment and a favorable evolution to prevent the sequelae.

Differential expression pattern of ZAC in developing mouse and human pancreas

ZAC is a transcription factor and cofactor, a strong candidate for transient neonatal diabetes mellitus (TNDM). TNDM involves impaired beta-cell development and is probably due to a double dose of ZAC, which is normally expressed only from the paternal copy. ZAC and Zac1 (its mouse orthologue) are strongly expressed in the proliferating progenitor/stem cells in many systems and also in some differentiated sites in human and mouse, suggesting a dual role in cell proliferation and differentiation control. Little is known about its expression in developing pancreas, the organ affected in TNDM. In this study, we examined ZAC/Zac1 expression in developing mouse and human pancreas by real-time PCR and dual in situ hybridization and immunofluorescence. Overall pancreatic expression drastically declined during gestation and early post-natal life in the mouse, and between the second trimester and adult in the human. Zac1 was predominantly expressed in mesenchyme in the mouse embryo, while ZAC was specifically expressed in islets of the human fetus. Thus, ZAC/Zac1 may play different roles in mouse and human pancreas development. The specific expression of ZAC in the human fetal beta-cells supports it as the gene involved in TNDM and the different expression pattern of Zac1 in mice from human may explain the much milder phenotype in the mouse model of ZAC double dose.

Transient neonatal diabetes mellitus type 1

Transient neonatal diabetes mellitus type 1 (TNDM1) is a rare but remarkable form of diabetes which presents in infancy, resolves in the first months of life, but then frequently recurs in later life. It is caused by overexpression of the imprinted genes PLAGL1 and HYMAI on human chromosome 6q24. The expression of these genes is normally restricted to the paternal allele as a result of maternal DNA methylation. TNDM1 is not associated with mutation of PLAGL1 or HYMAI, but rather with their overexpression via uniparental disomy, chromosome duplication, or relaxation of imprinting. Study of patients with TNDM1 has provided valuable insights into the causes of imprinting disorders. Over half of patients with maternal hypomethylation at the TNDM1 locus have additional hypomethylation of other maternally methylated imprinted genes throughout the genome, and the majority of these patients have mutations in the transcription factor ZFP57. TNDM1 with maternal hypomethylation has also been observed in patients conceived by assisted reproduction, and in discordant monozygotic twins. The variable clinical features of TNDM1 may be associated with variation in the nature of the underlying epigenetic and genetic mutations, and future study of this disorder is likely to yield further insights not only into the biological mechanisms of imprinting, but also into the contribution of epigenetics to diabetes.

Paternal uniparental isodisomy of chromosome 6 causing a complex syndrome including complete IFN-gamma receptor 1 deficiency

Mendelian susceptibility to mycobacterial disease (MSMD) is a rare primary immunodeficiency associated with clinical disease caused by weakly virulent mycobacterial species. Interferon gamma receptor 1 (IFN-gammaR1) deficiency is a genetic etiology of MSMD. We describe the clinical and genetic features of a 7-year-old Italian boy suffering from MSMD associated with a complex phenotype, including neonatal hyperglycemia, neuromuscular disease, and dysmorphic features. The child also developed necrotizing pneumonia caused by Rhodococcus equi. The child is homozygous for a nonsense mutation in exon 3 of IFNGR1 as a result of paternal uniparental disomy (UPD) of the entire chromosome 6. This is the first reported case of uniparental disomy resulting in a complex phenotype including MSMD.

Investigating parent of origin effects in studies of type 2 diabetes and obesity

The role of parent-of-origin effects (POE) in the etiology of complex diseases such as type 2 diabetes (T2DM) and obesity is currently of intense interest, but still largely unclear. POE are transmittable genetic effects whereby the expression of the phenotype in the offspring depends upon whether the transmission originated from the mother or father. In mammals, POE can be caused by genetic imprinting, intrauterine effects, or maternally inherited mitochondrial genes. In this paper, we describe the different mechanisms underlying POE, characterize known examples of POE in rare forms of diabetes, and review the evidence from linkage and association studies for POE in T2DM and obesity. Finally, we summarize some of the new and established statistical and experimental approaches commonly used to detect POE. Through this paper, we hope emphasizes the potentially significant importance of POE in the etiology of T2DM and obesity.

Fatal malonyl CoA decarboxylase deficiency due to maternal uniparental isodisomy of the telomeric end of chromosome 16

Malonic aciduria is a rare autosomal recessive disorder caused by deficiency of malonyl-CoA decarboxylase, encoded by the MLYCD gene. We report on a patient with clinical presentation in the neonatal period. Metabolic investigations led to a diagnosis of malonyl-CoA decarboxylase deficiency, confirmed by decreased activity in cultured fibroblasts. High doses of carnitine and a diet low in lipids led to a reduction in malonic acid excretion, and to an improvement in his clinical conditions, but at the age of 4 months he died suddenly and unexpectedly. No autopsy was performed. Molecular analysis of the MLYCD gene performed on the proband's RNA and genomic DNA identified a previously undescribed mutation (c.772-775delACTG) which was homozygous. This mutation was present in his mother but not in his father; paternity was confirmed by microsatellite analysis. A hypothesis of maternal uniparental disomy (UPD) was investigated using fourteen microsatellite markers on chromosome 16, and the results confirmed maternal UPD. Maternal isodisomy of the 16q24 region led to homozygosity for the MLYCD mutant allele, causing the patient's disease. These findings are relevant for genetic counselling of couples with a previously affected child, since the recurrence risk in future pregnancies is dramatically reduced by the finding of UPD. In addition, since the patient had none of the clinical manifestations previously associated with maternal UPD 16, this case provides no support for the existence of maternally imprinted genes on chromosome 16 with a major effect on phenotype.

Maternal microchimerism in peripheral blood in type 1 diabetes and pancreatic islet beta cell microchimerism

Maternal cells have recently been found in the circulation and tissues of mothers' immune-competent children, including in adult life, and is referred to as maternal microchimerism (MMc). Whether MMc confers benefits during development or later in life or sometimes has adverse effects is unknown. Type 1 diabetes (T1D) is an autoimmune disease that primarily affects children and young adults. To identify and quantify MMc, we developed a panel of quantitative PCR assays targeting nontransmitted, nonshared maternal-specific HLA alleles. MMc was assayed in peripheral blood from 172 individuals, 94 with T1D, 54 unaffected siblings, and 24 unrelated healthy subjects. MMc levels, expressed as the genome equivalent per 100,000 proband cells, were significantly higher in T1D patients than unaffected siblings and healthy subjects. Medians and ranges, respectively, were 0.09 (0-530), 0 (0-153), and 0 (0-7.9). Differences between groups were evident irrespective of HLA genotypes. However, for patients with the T1D-associated DQB1*0302-DRB1*04 haplotype, MMc was found more often when the haplotype was paternally (70%) rather than maternally transmitted (14%). In other studies, we looked for female islet beta cells in four male pancreases from autopsies, one from a T1D patient, employing FISH for X and Y chromosomes with concomitant CD45 and beta cell insulin staining. Female islet beta cells (presumed maternal) formed 0.39-0.96% of the total, whereas female hematopoietic cells were very rare. Thus, T1D patients have higher levels of MMc in their circulation than unaffected siblings and healthy individuals, and MMc contributes to islet beta cells in a mother's progeny.

Genetic and epigenetic defects at the 6q24 imprinted locus in a cohort of 13 patients with transient neonatal diabetes: new hypothesis raised by the finding of a unique case with hemizygotic deletion in the critical region

BACKGROUND

Transient neonatal diabetes (TND) is a rare form of diabetes usually present in the first few days after birth that resolves within 1 year but that has a tendency to recur later in life. It can be associated with chromosome 6 paternal uniparental disomy (UPD), paternal duplications or loss of maternal methylation at the 6q24 imprinted locus.

OBJECTIVE

To report on a cohort of 13 sporadic TND cases, including five with birth defects (congenital abnormalities of heart, brain and bone) and eight without.

RESULTS

The hallmarks of diabetes were similar in patients with or without 6q24 defects. The chromosome 6 abnormalities in our patients (n = 13) included 2 of 13 (approximately 15.4%) cases of paternal UPD6, 2 of 11 (approximately 18%) cases of complete and 3 of 11 (approximately 27%) cases of partial loss of the maternal methylation signature upstream of ZAC1-HYMAI imprinted genes in non-UPD cases, and 1 of 13 (approximately 7.7%) cases of hemizygotic deletion.

CONCLUSION

The deletion was found in a patient with severe congenital abnormalities. This genetic lesion was not reported previously. The hypothesis of an effect on regulatory elements critical for imprinting and tissue-specific gene expression in early development by the deletion is raised. The data presented here may contribute to the diagnosis and the understanding of imprinting in the region.

Fumarase deficiency caused by homozygous P131R mutation and paternal partial isodisomy of chromosome 1

We report on the first case of fumarase deficiency (FD) caused by uniparental isodisomy. An affected patient was found to be homozygous for the P131R mutation in the FH gene. In this nonconsanguineous family, the unaffected father was found to be heterozygous for the same mutation, and the mother was found to be homozygous wild-type. Analysis of chromosome 1 markers showed that the patient inherited both paternal alleles with complete absence of the maternal homolog. The two copies of the paternal chromosome 1 are heterodisomic for most of the chromosome except the distal 1q region which is isodisomic for the mutant alleles of the FH gene. The genotypes of other chromosome markers are consistent with the patient inheriting alleles from both parents. Although FD is an autosomal recessive disorder, the effects of uniparental disomy (UPD) should be considered in genetic counseling since the recurrence risk of an affected child is significantly reduced when the disorder is due to UPD.

Genetic and genomic systems to study methylmalonic acidemia

Methylmalonic acidemia (MMAemia) is the biochemical hallmark of a group of genetic metabolic disorders that share a common defect in the ability to convert methylmalonyl-CoA into succinyl-CoA. This disorder is due to either a mutant methylmalonyl-CoA mutase apoenzyme or impaired synthesis of adenosylcobalamin, the cofactor for this enzyme. In this article, we will provide an overview of the pathways disrupted in these disorders, discuss the known metabolic blocks with a particular focus on molecular genetics, and review the use of selected model organisms to study features of methylmalonic acidemia.

Neonatal diabetes mellitus: from understudy to center stage

PURPOSE OF REVIEW

Although neonatal diabetes mellitus is rare, its molecular basis has far-reaching implications for understanding the regulation of beta cell function, a prerequisite for understanding and treating type1 and type 2 diabetes mellitus especially by the manipulation of stem cells. The purpose of this review is to highlight the recent exciting discoveries concerning the genetic and molecular basis of the spectrum of disorders constituting neonatal diabetes mellitus.

RECENT FINDINGS

Recent reports in the literature, all in the past year, have identified activating mutations in the KATP channel that prevent its closure and hence insulin secretion as the major cause of permanent neonatal diabetes mellitus. Concurrently, a transgenic mouse model of transient neonatal diabetes mellitus due to mutations in ZAC/HYMAI provides an exquisite tool to study its human counterpart. Already, mutations in KATP and ZAC/HYMAI have been shown to be associated with type 1 and type 2 diabetes mellitus in later life; some mutations in KATP are amenable to treatment with sulfonylureas.

SUMMARY

The discoveries of the genes responsible for rarely occurring transient and permanent neonatal diabetes mellitus, and transgenic animal models to study them, are exciting milestones on the road to understanding and treating the common forms of type 1 and type 2 diabetes mellitus in children and adolescents.

Uniparental disomy (UPD) other than 15: Phenotypes and bibliography updated

Uniparental disomy (UPD) describes the inheritance of a pair of chromosomes from only one parent. The concept was introduced in Medical Genetics by Engel (1980); Am J Med Genet 6:137-143. Aside UPD 15, which is the most frequent one, up to now (February 2005) 197 cases with whole chromosome maternal UPD other than 15 (124 X heterodisomy, 59 X isodisomy, and 14 cases without information of the mode of UPD) and 68 cases with whole chromosome paternal UPD other than 15 (13 X heterdisomy, 53 X isodisomy, and 2 cases without information of the mode of UPD) have been reported. In this review we discuss briefly the problems associated with UPD and provide a comprehensive clinical summary with a bibliography for each UPD other than 15 as a guide for genetic counseling.

Neonatal diabetes, with hypoplastic pancreas, intestinal atresia and gall bladder hypoplasia: search for the aetiology of a new autosomal recessive syndrome

AIMS/HYPOTHESIS

Neonatal diabetes is a rare disease with several identified molecular aetiologies. Despite associations with other malformations, neonatal diabetes with intestinal and biliary anomalies has not been described. The current study aims to describe a new syndrome, and to examine a possible link with one of three genes known to cause neonatal diabetes.

METHODS

Five clinical cases are described. Immunohistochemical staining for pancreatic islet hormones was performed on three of the infants. DNA from one infant was analysed for abnormalities of the PLAGL-1 (ZAC), glucokinase and PDX-1 (IPF-1) genes.

RESULTS

Five infants (two sibling pairs from two families, and an isolated case) presented with neonatal diabetes, hypoplastic or annular pancreas, jejunal atresia, duodenal atresia and gall bladder aplasia or hypoaplasia. One sibling pair was born to consanguineous parents. One patient with a milder form is surviving free of insulin. Four children died in the first year of life despite aggressive medical management. Pancreatic immunohistochemistry revealed few scattered chromogranin-A-positive cell clusters but complete absence of insulin, glucagon and somatostatin. Exocrine histology was variable. In one case from the consanguineous family, molecular analysis showed no duplication or uniparental isodisomy of PLAGL-1 at 6q24, no contiguous gene deletion involving the glucokinase gene, and no mutation in the coding sequences or splice sites of PDX-1.

CONCLUSIONS/INTERPRETATION

This combination of multiple congenital abnormalities has not been previously described and probably represents a new autosomal recessive syndrome involving a genetic abnormality that interferes with normal islet development and whose aetiology is as yet unknown.

A novel gene for neonatal diabetes maps to chromosome 10p12.1-p13

We report a genomewide linkage analysis of a large consanguineous family segregating autosomal recessively inherited neonatal diabetes and the identification of a novel neonatal diabetes locus. Neonatal diabetes was characterized by low levels of circulating C-peptide with very low to undetectable levels of insulin in the presence of severe hyperglycemia unresponsive to insulin infusion. A dense genomewide linkage search of the family was undertaken using a first generation 10K single nucleotide polymorphism chip containing 10,044 markers. A region of homozygosity harboring the neonatal diabetes disease gene on chromosome 10p12.1-p13 was identified (multipoint logarithm of odds score 3.25). There is a strong history of type 2 diabetes in carriers of the disease gene. It is likely that chromosome 10p12.1-p13 may harbor a maturity-onset diabetes of the young or type 2 diabetes gene.

Transient neonatal diabetes, a disorder of imprinting

Transient neonatal diabetes (TND) is a rare but distinct type of diabetes. Classically, neonates present with growth retardation and diabetes in the first week of life. Apparent remission occurs by 3 months but there is a tendency for children to develop diabetes in later life. Evidence suggests it is the result of overexpression of an imprinted and paternally expressed gene/s within the TND critical region at 6q24. Two imprinted genes, ZAC (zinc finger protein associated with apoptosis and cell cycle arrest) and HYMAI (imprinted in hydatidiform mole) have been identified as potential candidates. Three genetic mechanisms have been shown to result in TND, paternal uniparental isodisomy of chromosome 6, paternally inherited duplication of 6q24, and a methylation defect at a CpG island overlapping exon 1 of ZAC/HYMAI.

Transient neonatal diabetes mellitus, type 4, type 1 diabetes mellitus, or MODY: which disease is it, anyway?

A 30year-old Hispanic male who presented with transient neonatal diabetes mellitus at 4 months has been intensively studied with 12 islet-cell secretagogues from 4 months to 24 years. He was both ICA- and GAD-65-negative, but at 28 years was diagnosed with hypothyroidism due to positive thyroperoxidase antibodies. The course of his disease(s) and the various presentations of hyperglycemia are documented and illustrated by the responses in islet cell hormone secretion, namely, insulin, glucagon, and C-peptide. Insulin secretion gradually fell over 24 years, glucagon secretion persisted from infancy to 24 years but was only minimal during i.v. glucose at 24 years, and C-peptide secretion remained normal, although modest, throughout the 24 years. These data suggest that, despite changing presentations of diabetes mellitus over time, the islets continued to process proinsulin, although the patient required insulin therapy.

Genome-wide linkage analysis assessing parent-of-origin effects in the inheritance of type 2 diabetes and BMI in Pima Indians

We examined the hypothesis that imprinted genes may affect the propensity to type 2 diabetes and obesity in Pima Indians. Multipoint variance component methods were used to assess linkage of BMI (kg/m(2)) and age-adjusted diabetes to loci derived from either father (LOD(FA)) or mother (LOD(MO)) in a genome-wide scan. Tentative evidence of loci where imprinted genes might be acting was found for diabetes with maternally derived alleles on chromosomes 5 (LOD(MO) = 1.5) and 14 (LOD(MO) = 1.6). Evidence of linkage of BMI to maternally derived alleles was found on chromosome 5 (LOD(MO) = 1.7) and to paternally derived alleles on chromosome 10p (LOD(FA) = 1.7). Additional analyses of sibling pairs who were affected by diabetes and younger than 25 years of age showed an increase of sharing of maternally derived alleles on chromosome 6 (LOD(MO) = 3.0). We also examined sites of a priori interest where action of imprinted genes has been proposed in diabetes or obesity. We found no evidence of parent-specific linkage (of either diabetes or BMI) on chromosome 11p, a region that contains several imprinted genes, but observed weak evidence of linkage of diabetes to paternally derived alleles (LOD(FA) = 0.9) in the region of chromosome 6q, believed to contain an exclusively paternally expressed gene or genes that cause transient neonatal diabetes mellitus. In conclusion, we determined regions of interest on chromosomes 5, 6, and 10 where imprinted genes might be affecting the risk of type 2 diabetes or obesity in Pima Indians.

Transient neonatal diabetes mellitus in a child with paternal uniparental disomy of chromosome 6

We report a male infant with transient neonatal diabetes mellitus (TNDM; MIM 601410), macroglossia, hypertelorism, umbilical hernia, inguinoscrotal hernia and onychomycosis. Diabetes mellitus was diagnosed 10 days after birth and resolved after 6.5 months of treatment. Genetic investigation indicated the presence of paternal uniparental disomy of chromosome 6 (UPD 6). The finding of paternal UPD 6 allows prediction of a transient, rather than permanent NDM, and no increased recurrence risk of TNDM in subsequent pregnancies. Therefore, finding of NDM should be a strong indicator for genetic testing.

Neonatal diabetes mellitus: patient report and review of the literature

A female infant born at 33 weeks gestation to a gestationally diabetic mother developed apnea and respiratory distress at 6 hours of age. Laboratory investigation demonstrated persistent hyperglycemia, and the patient was treated with continuous intravenous and subsequent subcutaneous insulin therapy. Detailed laboratory investigation to reveal the etiology of hyperglycemia and further endocrine evaluation were not significant. The baby's insulin requirement has continued thereafter, and she is being followed up in an outpatient clinic still under insulin therapy at 18 months of age. Neonatal diabetes mellitus should be considered in the differential diagnosis of neonatal hyperglycemia, and it may develop in newborns born to diabetic mothers, as well as neonatal hypoglycemia. Insulin treatment with close blood glucose monitoring is essential as long as hyperglycemia persists since neonatal diabetes mellitus may be either transient or permanent and it is not possible to differentiate these two outcomes before 18 months of age.

Origin of uniparental disomy 6: presentation of a new case and review on the literature

Paternal uniparental disomy (UPD) of chromosome 6 has been reported several times in patients with (transient) neonatal diabetes mellitus ((T)NDM). Here we present our short tandem repeat typing results in a new patient with NDM, revealing a paternal isodisomy (UPiD). Summarising these data with those published previously on complete paternal (n=13) and maternal (n=2) UPD6, all cases show isodisomy. In general, several modes of UPD formation have been suggested: While a meiotic origin of UPD mainly results in a uniparental heterodisomy (UPhD), UPiD is probably the result of a post-zygotic mitotic error. This mode of formation consists of a mitotic nondisjunction in a disomic zygote, followed by either a trisomic rescue or a reduplication. Endoduplication in a monosomic zygote is another possible but less probable mechanism, taking into consideration that monosomic zygotes are not viable. The exclusive finding of isodisomy in case of chromosome 6 therefore gives strong evidence that segregational errors of this chromosome are mainly influenced by postzygotic factors. This hypothesis is supported by the observation of two cases with partial paternal UPiD6 originating from mitotic recombination events. The influence of mitotic segregational errors in UPD6 formation is in agreement with the results in trisomy/UPD of other chromosomes of the C group (7 and 8), and is in remarkable contrast to the findings in studies on the origin of the frequent aneuploidies. Multiple factors ensure normal segregation and we speculate that they vary in importance for each chromosome.

Partial paternal uniparental disomy of chromosome 6 in an infant with neonatal diabetes, macroglossia, and craniofacial abnormalities

Neonatal diabetes, which can be transient or permanent, is defined as hyperglycemia that presents within the first month of life and requires insulin therapy. Transient neonatal diabetes mellitus has been associated with abnormalities of the paternally inherited copy of chromosome 6, including duplications of a portion of the long arm of chromosome 6 and uniparental disomy, implicating overexpression of an imprinted gene in this disorder. To date, all patients with transient neonatal diabetes mellitus and uniparental disomy have had complete paternal isodisomy. We describe a patient with neonatal diabetes, macroglossia, and craniofacial abnormalities, with partial paternal uniparental disomy of chromosome 6 involving the distal portion of 6q, from 6q24-qter. This observation demonstrates that mitotic recombination of chromosome 6 can also give rise to uniparental disomy and neonatal diabetes, a situation similar to that observed in Beckwith-Wiedemann syndrome, another imprinted disorder. This finding has clinical implications, since somatic mosaicism for uniparental disomy of chromosome 6 should also be considered in patients with transient neonatal diabetes mellitus.

HLA-DRB1 and DQB1 genotypes in patients with insulin-dependent neonatal diabetes mellitus. A study of 13 cases

Insulin-dependent neonatal diabetes mellitus (NDM) is a rare form of diabetes with a heterogeneous genetic background. The HLA-DRB1 and DQB1 genotypes were determined for 13 patients with NDM, from 9 unrelated families. Four patients had permanent NDM (PNDM) and 9 patients had transient NDM (TNDM). No excess of HLA susceptibility markers for type 1 diabetes (IDDM) was observed in this series of patients, whatever the forms of diabetes PNDM or TNDM. Paternal isodisomy of chromosome 6 was observed in two TNDM cases. These observations are consistent with the current hypothesis that there is a recessive susceptibility gene, at least in the transient form of the disease, unlinked to the MHC locus on chromosome 6. Although established in a short series, our results do not support an additive role of IDDM1 in the progression of the disease.

Confined placental mosaicism and genomic imprinting

The concept of confined placental mosaicism and its relationship to genomic imprinting and uniparental disomy is explained in this chapter. Clinically significant imprinting syndromes, such as Prader-Willi syndrome, Angelman syndrome, Beckwith-Wiedemann syndrome, Silver-Russell syndrome and transient neonatal diabetes mellitus, potentially associated with confined placental mosaicism are described and referenced. Non-Mendelian inheritance of recessive mutations in uniparental disomy is illustrated. Both skewed X chromosome inactivation and isolated gonadal mosaicism are outlined as newly recognized consequences of post-zygotic chromosomal mutation and confined placental mosaicism. Clinical management of pregnancies with confined placental mosaicism is proposed as well as future research directions in the field of confined placental mosaicism and its consequences.

Transient but not permanent neonatal diabetes mellitus is associated with paternal uniparental isodisomy of chromosome 6

OBJECTIVES

The factors determining the pathogenesis of transient and permanent neonatal diabetes mellitus are poorly characterized. The purpose of this study was to examine the role of chromosome 6 in the pathogenesis of neonatal diabetes mellitus and to detect differences between these 2 phenotypes.

METHODS

Microsatellite markers (D6S334, D6S286, D6S310, D6S308, D6S292, D6S311, and D6S403) and human leukocyte antigen DQ alleles were examined using polymerase chain reaction and DNA fragment electrophoresis in 3 patients with transient and 3 patients with permanent neonatal diabetes mellitus. Humoral markers of islet cell autoimmunity and clinical characteristics were analyzed in the 2 groups.

RESULTS

A patient with transient neonatal diabetes mellitus (TND) and macroglossia carrying paternal uniparental isodisomy (UPD) of chromosome 6 has been identified. The isodisomy affected the whole chromosome; no maternal chromosome 6 sequences were detected. The permanent neonatal diabetes mellitus cases and the other 2 cases with TND did not have UPD. None of the patients had high-risk type 1 diabetes human leukocyte antigen DQ alleles and most infants were negative for islet cell-specific autoantibodies indicating that none of the 2 forms of neonatal diabetes mellitus is likely to be of autoimmune origin. An association of TND and persistent granulocytopenia is described for the first time.

CONCLUSIONS

We propose that transient and permanent forms of neonatal diabetes mellitus have different genetic background and represent different disease entities. TND is associated with UPD of chromosome 6 suggesting that an imprinted gene on chromosome 6 is responsible for this phenotype. It seems that 2 copies of the paternal allele are necessary for the development of TND; therefore, it is likely that overexpression of a putative gene located on chromosome 6 alters pancreatic beta-cell maturation and insulin secretion.

Molecular cytogenetics of a de novo interstitial deletion of chromosome arm 6q in a developmentally normal girl

Using fluorescence in situ hybridization and microsatellite analysis, we have characterized a de novo interstitial deletion on the long arm of chromosome 6 [46,XX,del(6) (q23.3q24.2)] in a developmentally normal girl with very mild phenotypic abnormalities. The deletion was paternal in origin and was between markers WI-5023 and D6S1042. The size of the deletion was estimated to be approximately 4-5 Mb. The normal phenotype in this patient might be the result of imprinting of paternal copies of genes located in the segment 6q23. 3-q24.2. Alternatively, the genes located in the segment 6q23.3-q24. 2 might not be subject to dosage effects and therefore the haploinsufficiency of genes in this segment might not have phenotypic consequences.

Syndromal obesity due to paternal duplication 6(q24.3-q27)

The likelihood of a paternally expressing imprinted gene in chromosome region 6(q23-24) has been highlighted by cases of transient neonatal diabetes mellitus (TNDM) in which paternal uniparental disomy (UPD) for chromosome 6 or paternal duplication 6(q23-qter) was detected. We present the case of a 38-year-old man with moderate to severe intellectual delay, short stature, small hands and feet, eye abnormality, small mouth, and obesity (without hyperphagia) beginning in mid-childhood. The perinatal and neonatal histories were normal. The patient had a duplication within 6q. Fluorescence in situ hybrisation studies were performed with single and dual hybridisations using a chromosome 6 library probe, short and long arm subregional probes, 6q23-24, 6q25.3-6qter locus-specific probes, and a 6q telomere probe. The hybridisation results defined an inverted duplication of 6q24.3 to 6q27. DNA studies with microsatellite markers from 6p and 6q showed regular biparental inheritance of chromosome 6 and confirmed that the duplication was paternal in origin. Our patient appears to be the first one known to have paternal duplication of chromosome area 6(q24-q27) who did not have TNDM as an infant. He has remained nondiabetic, although obesity, without hyperphagia, has been a constant problem since its onset in mid-childhood.

Localisation of a gene for transient neonatal diabetes mellitus to an 18.72 cR3000 (approximately 5.4 Mb) interval on chromosome 6q

Transient neonatal diabetes mellitus (TNDM) is a rare condition which presents with intrauterine growth retardation, dehydration, and failure to thrive. The condition spontaneously resolves before 1 year of age but predisposes patients to type 2 diabetes later in life. We have previously shown that, in some cases, TNDM is associated with paternal uniparental disomy (UPD) of chromosome 6 and suggested that an imprinted gene responsible for TNDM lies within a region of chromosome 6q. By analysing three families, two with duplications (family A and patient C) and one with several affected subjects with normal karyotypes (family B), we have further defined the TNDM critical region. In patient A, polymorphic microsatellite repeat analysis identified a duplicated region of chromosome 6, flanked by markers D6S472 and D6S311. This region was identified on the Sanger Centre's chromosome 6 radiation hybrid map (http://www.sanger.ac.uk/HGP/Chr6) and spanned approximately 60 cR3000. Using markers within the region, 418 unique P1 derived artificial chromosomes (PACs) have been isolated and used to localise the distal breakpoints of the two duplications. Linkage analysis of the familial case with a normal karyotype identified a recombination within the critical region. This recombination has been identified on the radiation hybrid map and defines the proximal end of the region of interest. We therefore propose that an imprinted gene for TNDM lies within an 18.72 cR3000 (approximately 5.4 Mb) interval on chromosome 6q24.1-q24.3 between markers D6S1699 and D6S1010.

Paternal uniparental disomy of chromosome 6 and transient neonatal diabetes mellitus

Transient neonatal diabetes mellitus occurs in growth-retarded infants, has an incidence of 1 in 400000 live births and has been associated with both paternal uniparental disomy of chromosome 6 and paternal duplications of 6q. We analysed samples from our cohort of patients with transient neonatal diabetes mellitus for uniparental disomy of chromosome 6 using polymorphic microsatellite repeat analysis. We report here the fifth case of paternal uniparental disomy of chromosome 6 associated with classic transient neonatal diabetes mellitus and estimate that uniparental disomy of chromosome 6 accounts for approximately one fifth of cases of transient neonatal diabetes mellitus.

Mapping of murine diabetogenic gene mody on chromosome 7 at D7Mit258 and its involvement in pancreatic islet and beta cell development during the perinatal period

Mutation of the murine maturity-onset diabetes mellitus of the young (Mody) locus induces diabetes, but the effects of its homozygosity on the pancreas remain unknown. F2 mice were obtained by F1 (diabetic C57BL6 x normal Mus musculus castaneus) crosses. About 20% of the F2 progeny developed diabetes by 2 wk of age, 50% of the progeny were normal at 2 wk and developed diabetes between 5 and 8 wk of age, and the remaining 30% did not develop diabetes. Quantitative trait locus analysis using blood glucose levels of 118 F2 mice at 2 wk of age and 5-8 wk of age located Mody within 3 cM of D7Mit258. Histopathological investigation revealed hypoplastic islets (approximately 33% of that of wild-type mice) and a lower density of beta cells (approximately 20% of wild-type) with a reciprocal dominance of alpha cells (four times that of wild-type) in Mody homozygotes. Electron microscopic observations revealed a specific decrease in the number of insulin secretory granules and a lower density of beta cells. Ratios of insulin to glucagon contents confirmed specific decreases in insulin content: 0.01 for homozygotes, 0.54 for heterozygotes, and 1.11 for wild-type mice on day 14. These results suggest that Mody is involved in both islet growth and beta cell function.

Organisation of the human PAX4 gene and its exclusion as a candidate for the Wolcott-Rallison syndrome

Neonatal diabetes mellitus is a rare condition, the causes of which are mostly unknown. One well defined though very rare entity is the autosomal recessive Wolcott-Rallison syndrome, in which permanent neonatal diabetes, osteopenia, and epiphyseal dysplasia occur. Only five previous families have been reported, and here we describe the second in which parental consanguinity was present. The proband was born to first cousin parents and died at 2 years from the sequelae of poorly controlled diabetes. To test the hypothesis that mutation of PAX4, required in the mouse for pancreatic islet beta cell development, might cause WRS, the structure of the human PAX4 gene was deduced and DNA from two unrelated WRS patients sequenced. No PAX4 mutation was present, though the entire coding region was sequenced in both patients. It therefore appears unlikely that PAX4 is involved in the aetiology of Wolcott-Rallison syndrome, though it remains a good candidate for other forms of neonatal diabetes mellitus.

Growth effects of uniparental disomies and the conflict theory of genomic imprinting

While numerous theories have been proposed for the evolution of genomic imprinting, few have been tested. The conflict theory proposes that imprinting is an intra-individual manifestation of classical parent-offspring conflict. This theory is unique in predicting that imprinted genes expressed from the paternally derived genome should be enhancers of pre- and post-natal growth, while those expressed from the maternally derived genome should be growth suppressors. We examine this prediction by reviewing the literature on growth of human and mouse progeny that have inherited both copies (or part thereof) of a particular chromosome from only one parent. Perhaps surprisingly, we find that much of the data do not support the hypothesis.

Paternal uniparental disomy for chromosome 6 causes transient neonatal diabetes

We report an infant with intrauterine growth retardation and transient neonatal diabetes who has paternal uniparental disomy for chromosome 6. The infant was not dysmorphic and had no congenital anomalies. To our knowledge, this is the third case of paternal uniparental disomy occurring in an infant with transient neonatal diabetes, thus confirming the association.