GENETIC SPECTRUM OF NEONATAL DIABETES
Kocova M
*Corresponding Author: Mirjana Kocova, M.D., Ph.D., Medical Faculty, University Cyril and
Methodius, 50 Divizija No. 6, 1000, Skopje, Republic of Macedonia. Tel. +389-7024-2694. Fax:
+389-2317-6167. E-mail: mirjanakocova@yahoo.com
page: 5
|
|
INTRODUCTION
Most of the patients with diabetes mellitus (DM) in
childhood suffer from DM type 1 (DMT1) that is of autoimmune
etiology [1,2]. This form of diabetes appears after
the first 6 months of life, and reaches the highest incidence
in the 9-14 years age group, with the rising incidence in
the age group before 4 years of age [3]. The persisting
hyper-glycemia is due to autoimmune destruction of insulin
producing β-cells in the endocrine pancreas leading
to insulin deficiency. It is considered a polygenic disease
involving mostly DQ and DR human leukocyte antigen
(HLA) genes conferring susceptibility or resistance toward
the disease [4-8]. Diabetes mellitus type 1 accounts for
more than 95.0% of cases in childhood [7,9,10]. During the
last few decades, obesity in childhood has caused increase
of DM type 2 (DMT2) in children, which is induced by
an interplay of genetic and environmental factors. Genetic
factors involved in DMT2 are still not precisely elucidated.
A number of different gene polymorphisms affecting β-cell
function causes impaired insulin secretion or insulin resistance
[11,12]. The prevalence of DMT2 in childhood and
adolescence varies in different countries, reaching up to
30.0% of all cases with DM in regions with the highest
childhood obesity rates [1].
Monogenic diabetes (MD) caused by mutations of
a single gene is a separate form of DM with a distinct
etiology, clinical presentation, therapy and outcome. Monogenic
diabetes is a heterogenous group of sub-forms of
diabetes caused by mutations in different, highly penetrant
genes that are pivotal for pancreas development, sensing
of the level of glucose for insulin secretion, cellular metabolism,
cell membrane depolarization control, or insulin
synthesis/excretion [13-19]. Monogenic diabetes is not
common, but it does account for 1.0-6.0% of pediatric
diabetes cases [20].
Generally, based upon the detected mutation, timing
of presentation, and affected genes, MD can be classified
as follows [19]: 1) neonatal diabetes (ND) (occurring before
6 months), 2) syndromic ND associated with extra
pancreatic features, and 3) autosomal dominant familial
hyperglycemia or diabetes or maturity onset diabetes of
the young (MODY). This review will give an overview
of mutations causing diabetes in the neonatal period that
includes ND and syndromic diabetes.
Genes Involved in Monogenic Diabetes. Mutations
in about 40 different genes are recognized as a cause of
MD. These encompass genes involved in different processes
that could compromise insulin secretion and action
such as: reduction of β-cell number or pancreatic aplasia,
impaired β-cell development, glucose sensing or metabolism,
failure to depolarize cellular membrane and expulsion
of insulin in circulation, failure of insulin synthesis,
increased destruction of β-cells including immune-based destruction, increased apoptosis, and endoplasmatic reticulum
stress, as well as other mechanisms that need to be
elucidated [21-23]. Each of these steps in insulin secretion
and action is under the control of a particular gene [19,24]
(Tables 1 and 2).
Most of the recent molecular analyses in MD have
been performed by Sanger sequencing using specific primers,
or targeted next generation sequencing (NGS) of involved
exons and searching for multiple gene mutations
[25-28]. We have reviewed most of the recent guidelines
for the diagnosis and treatment of all forms of ND, as well
as numerous original articles describing characterizations
of ND caused by different mutations.
Neonatal Diabetes. Although the neonatal period
encompasses only the first 4 weeks of postnatal life, the
term ND, by convention, is used for the DM that appears
in neonates and infants up to 6 months of age, although
some forms might appear up to 9-12 months of age [20,24].
It was first described in 1852 and has been reported since
then in different countries and ethnicities around the world
[24,28-33]. If the hyperglycemia appears in the infant of
6-12 months, the distinction of the ND form early onset of
DMT1 is necessary [34]. However, most of the patients do
not display autoimmunity at this early age and belong to
the monogenic “neonatal diabetes” [35]. The MODY mutations
are present at birth, and they cause the appearance of
diabetes later in life. Neonatal diabetes is rare, it appears,
according to different authors, in one case per 100,000,
300,000 or even per 500,000 live births [19,23,36,37].
It can be classified as: transient ND mellitus (TNDM),
and permanent ND mellitus (PNDM) [19,24,34,38,41].
Aguillar-Bryan et al. [24] have collected more than 195
patients from different studies and calculated that TNDM
is more frequent, affecting 57.0% (111/ 195) of all neonates
with ND.
Transient Neonatal Diabetes Mellitus. Transient
ND mellitus appears in the first days or weeks after birth,
usually in newborns with intrauterine growth retardation
(IUGR). After introduction of low doses of insulin therapy,
it resolves, usually approximately up to 4 months of age, but its duration could be extended up to 18 months [35-
38]. However, during adolescence or in the young adult
period, relapses can occur in about 50.0% of patients, when
it resembles DMT2 [36-38]. Genes involved in TNDM are
provided in Table 1.
The genetic origin of TNDM has been established for
approximately 90.0% of patients with TNDM. The major
genetic change causing the disease is abnormal imprinting
at chromosome 6q24, which appears in approximately
70.0% of patients with TNDM [36,39,40-43]. Usually,
for this chromosome region, only alleles inherited from
the father are expressed, whereas mother’s alleles are imprinted.
Overexpression of paternal genes in this region
can happen through uniparental isodisomy or inheritance
of the duplication of the region from the father [44,45].
On the other hand, defects in maternal methylation of the
6q24 region can cause activation of the maternal alleles
[46,47]. The methylation defect might be inherited or can
appear sporadically. The 6q24 region is rich in imprinted
genes. Only a few of them have been studied in detail,
such as the ZAC and HYMA1 genes. The regulator of the
methylation of this chromosome region is the ZFP57 gene.
ZAC (zinc finger protein that regulates apoptosis and cell
cycle arrest) is a multifunctional transcription factor and
coactivator of p53 and coactivator or corepressor of some
nuclear hormone receptors [48]. ZAC has been described
as a tumor suppressor gene and its overexpression in cell
lines has shown decreased rate of cell replication, increased
apoptosis and cell mitosis G1 arrest [49]. Thus, when overexpressed,
it would reduce growth of the β-cell mass,
possibly through increase of the peroxisome proliferatoractivated
receptor γ (PPARγ) expression, which is an insulin
sensitizer, during embryogenesis and slow down the
β-cell proliferation. The function of HYMAI (hydatiform
mole-associated and imprinted also called PLAGL1) has
still to be elucidated. These methylation defects have the
following effects: decreased cell replication, increased
apoptosis, delayed maturation of pancreatic islets, and decreased β-cell mass that cause impaired insulin secretion
in utero and after birth. DNA multiple methylation
defects can also appear and they are usually caused by
mutation in the ZFP57 gene when TNDM is only a part
of the complex clinical picture [49]. Most of these facts
have been confirmed in the mouse model [50].
Approximately 30.0% of children with TNDM have
additional features such as umbilical hernia or macroglossia
[43]. Insulin therapy is necessary, however, the dose is
quickly tapered-down and not necessary after 12 weeks
[19]. The relapse is usually common during puberty, it appears
in 50.0-60.0% of patients and is presented as DMT2.
Due to some residual degree of endogenous insulin secretion,
many patients are successfully treated with sulfonylurea
[51,52]. If the cause of the disease is duplication of the
parental 6q24 region, the genetic risk for future children
should be discussed with the family.
Transient ND mellitus can also be caused by mutations
of the ABCC8 and KCNJ11 genes, and their function
will be discussed with PNDM, as these two mutations can
cause both TNDM and PNDM. Transient ND mellitus
has rarely been described in association with HNF1 β
mutations, causing pancreatic hypoplasia and associated
prenatal cystic kidney [53], autosomal recessive insulin
gene mutations [54], or homozygous glucokinase (GCK)
mutation inherited from both parents in consanguineous
families (Table 1). These genes and their mutations will
be discussed in the section on PNDM.
Permanent Neonatal Diabetes Mellitus. Permanent
ND mellitus has a very similar clinical presentation as
TNDM, and can be distinguished only on the basis of
the gene mutations, especially in hyperglycemic children
with a low birth weight [55]. This diabetes is permanent,
remission does not occur. About 10 genes are involved in
the etiology of PNDM causing abnormal pancreatic development,
increased apopotosis, reduction of β-cell mass
and β-cell dysfunction. However, the most common mutations
are in the KCNJ11 and ABCC8 genes, which account
for approximately 30.0% of all PNDM cases, INS gene
mutations accounting for 12.0%, and glucokinase (GCK
gene) mutations. All of these genes are involved in glucose
sensing and insulin secretion [19,24,55-57]. The function
of these genes has been elucidated in Table 2 (Figure 1).
Channelopathies. KCNJ11 and ABCC8 gene mutations
are responsible for approximately 40.0% of permanent
or transient hyperglycemia (NDM) cases [56,58].
Most of them (approximately 60.0%) occur de novo. They
act through increase of activity of ATP-sensitive potassium
channels located on the β-cell membrane [35,59,60].
Glucose enters the cell facilitated by the Glut1 transporter,
and the enzyme glucokinase (GCK) converts it to glucose-
6-phosphate that is then transferred into mitochondria.
There, increased metabolic activity induces an increase of
ATP/ ADP ratio that results in a closure of the membrane
KATP channel. As a result, the β-cell membrane gets depolarized,
followed by influx of Ca++ into the cell, which
triggers insulin secretion and expulsion from the β-cell
[57,59] (Figure 1). The KATP channel is a key component
of the glucose stimulated insulin secretion pathway. It
is composed of four Kir6.2 subunits that compose the
K+ conducting pore encoded by the KCNJ11 gene. Four
SUR1 regulatory subunits encoded by the ABCC8 gene
are located at the external site of the pore and regulate
the channel activity. Dominant activating mutations in
KCNJ11 or ABCC8 cause a permanently opened KATP channel,
irrespective of the glucose level, which decreases the
channel sensitivity toward ATP, disables the membrane depolarization
and prevents insulin secretion causing NDM
[57-59]. More than 205 different mutations of the KCNJ11
and 748 of the ABCC8 genes have been reported [59-65]
Many additional polymorphisms with significance to be
elucidated also have been referred [65]. Mutations in the
KCNJ11 gene are usually located at the N or C terminus
below the plasma membrane, around the inhibitory ATP
binding site, and they reduce affinity for ATP. The ABCC8
gene mutations, on the other hand, are located throughout
the entire molecule, however, the mechanism of the channel
activation is poorly understood although it has been
suggested that SUR1 acts to antagonize the Mg-dependent
stimulatory action on Kir6.2 [61,64]. Mutations could
be point mutations, e.g. missense, nonsense, frameshift,
splicing mutations and deletions [65]. Depending upon
the mutations, different numbers of permanently opened
KATP channels and their different sensitivity for flux of ATP
occurs, thus causing PNDM or TNDM. A complex interplay
between Kir6.2 and SUR1 subunits, also involving Mg++ has been described [66]. KCNJ11 and SUR1 gene
mutations occur de novo in 80.0% of patients without
family history, causing isolated PNDM. The remaining
cases are familial, and they are always dominantly transferred.
KCNJ11 gene mutations cause PNDM in 90.0% of
patients who carry it, whereas the ABCC8 gene mutations
causes PNDM in less than 40.0% of patients. The remaining
10.0% and >60.0% of mutations, respectively cause
TNDM [65]. Both KCNJ11 and ABCC8 genes are located
on chromosome 11p, 4.5 kb apart. KCNJ11 encodes for the
390-amino acid Kir6.2 protein, and ABCC8 consists of 39
exons. It encodes for the SUR1 (sulphonyl-urea receptor)
protein that consists of 1582 amino acids [65].
Permanent ND mellitus due to KCNJ11 and ABCC8
gene mutations usually have an acute clinical presentation
in neonates at the age from several days of age up to 26
weeks after birth, who are born with a lower birth weight,
but not as low as in TNDM [67]. Extreme hyperglycemia,
severe dehydration, ketoacidosis hypoinsulinemia,
and immediate insulin dependency are the common set
of symptoms [19,24,68]. However, milder forms have
been described in certain mutations [24,60]. Due to the
confirmed expression of KATP channels in muscle cells
and neurons, approximately 20.0-30.0% of patients have
associated neurological features, which are usually associated
with certain mutations such as V59M or R210
C of the KCNJ11 gene [65,69-72]. Some of the children
have PNDM, muscle weakness and hypotonia associated
with epilepsy when this is termed DEND (developmental
delay, epilepsy, ND) syndrome [71]. Others have different
level of developmental delay, lower IQ, may have
attention deficit hyperactivity disorder (ADHD), autism,
anxiety, hypotonia, muscule weakness, balance problems,
learning disabilities, and are termed iDEND (intrermediate
DEND) syndrome. The V59M mutation has mostly
been blamed for iDEND. In general, patients have lower
academic achievements [72-74]. There are some data confirming
that mutations that increase channel activity less
than 15-fold are associated with both PNDM and TNDM,
whereas, if the channel activity is more than 15-fold higher,
DEND syndrome occurs [24]. Breakthrough in the treatment
of children with PNDM occurred when sulfonylurea
was shown to be a successful therapy that normalizes the
function of the KATP channel [75,76] but also improves,
to some extent, the developmental issues if given early
enough [77]. Beyond 90.0% of patients with PNDM can
be transferred from insulin to sulfonylurea and treated
long-term with careful tapering of the doses that provides
a very stable, long-term glycemic control [76,78]. However,
in the review by Aguilar-Bryan and Bryan [24], 22
different KCNJ11 gene mutations had a good response to
sulfonylurea, whereas seven did not, whereas 20 ABCC8
gene mutations had a good response vs. three mutations
where the response did not occur. In the patients who did
not react favorably to sulfonylurea, therapy with insulin
was necessary [24]. Therefore, genetic testing is mandatory
for individualized treatment, improved outcome, and
a better quality of life (QoL) [58,79-81].
Insulin gene mutations. Dominant mutations of the
insulin gene (INS) are the second most frequent cause of
PNDM [82,83]. Mutated genes usually appear de novo in
80.0% of cases, and cause disturbances in the folding of
the proinsulin and/or insulin protein that becomes nonfunctional,
but additionally causes endoplasmic reticulum
stress due to protein accumulation inducing apoptosis of
the β-cell [56]. No other tissues or organs are affected.
A significant portion of mutations are de novo, usually
dominant, and affect the disulfide bonds in the insulin
molecule [84]. Diabetes is typically insulin-deficient, affected
newborns have a low birth weight, hyperglycemia
usually occurs during the second month of life. It can occasionally
appear after the age of 6 months, and therefore,
in all babies with negative anti β-cell antibodies, molecular
testing for insulin gene mutations is necessary. Insulin gene
mutations causing PNDM can also be recessive, causing
delayed fetal growth, low birth weight, and severe early
presentation after birth [82,83]. All newborns with a mutation
of the insulin gene require insulin therapy.
Glucokinase mutations. Glucokinase is the enzyme
that regulates adequate glucose-stimulated insulin secretion
from the β-cell, and is termed a sensor for glucose [85].
In humans, the threshold of glycemia for insulin release is
set to approximaltely 5 mmol/L. More than 200 mutations
have been detected in the GCK gene. However, most of
them being autosomal dominant mutations, if in heterozygous
form, cause MODY2, e.g. mild hyperglycemia due to
the inappropriate sensing of glucose level. They are usually
detected later in childhood or during young adult life.
However, several homozygous inactivating mutations are
described in PNDM [86,87]. Recessive mutations, when
in homozygous or compound homozygous states, cause
complete lack of insulin secretion and PNDM, especially in
consanguineous families. Parents usually have a history of
low glucose tolerance or untreated mild diabetes. This form
of diabetes accounts for only 2.0-3.0% of all patients with
PNDM [88]. These neonates have low body mass due to
insulin deficiency and are treated with insulin. Mutations of
other genes causing ND are rare, and are given in Table 1.
Syndromic Neonatal Diabetes Mellitus. Syndromic
ND mellitus (SNDM) should be considered after more
common forms (KATP channelopathies) and other more
frequent mutations are excluded. The number of genes
discovered inducing SNDM is increasing with the newer
molecular techniques. Most cases of SNDM belong to syndromes with associated extra-pancreatic features affecting
different organs or functions. All are very rare, some with
only a few patients described. All require therapy with
insulin, and other therapeutic procedures for associated
problems. Major characteristics have been presented in
Table 2. Only some will be mentioned briefly.
Eukaryotic initiation factor 2α kinase 3 (EIF2AK3)
mutations in homozygotes or compound heterozygotes
cause Wolcott-Rallison syndrome. It is the most common
form of PNDM in consanguineous families. Clinical
presentation is complex, and comprises additional features
such as multiple epiphyseal dysplasia, growth retardation,
occasionally associated with learning difficulties, epilepsy,
hepatic and/or renal dysfunction, abnormalities of the cardiovascular
system and dysfunction of the exocrine pancreas
[89,90]. The location of this gene is at chromosome
2p12 and it is involved in the regulation of protein-folding
in the endoplasmic reticulum [90,91]. If mutated, it causes
endoplasmic stress and initiates apoptosis in many tissues
including β-cells. About 20 different mutations have so
far been reported, children present with ketoacidosis and
insulin therapy is mandatory [24,91,92].
Mutations in the WFS1 gene cause Wolfram syndrome.
It is a very complex syndrome, also known as DIDMOAD,
symptoms consisting of DM, diabetes insipidus,
optic atrophy, deafness as well as neurodegeneration. It
appears in 1:160,000-1:770,000 individuals. Although, on
average it appears at 6 years of age, neonatal cases have
been described with insulin-dependence, and additional
features during childhood. The β-cell degeneration due to
irregular folding of the protein wolframin, induces endoplasmic
stress in different organs [93-95]. Mutations can be
autosomal recessive, however, several dominant mutations
have also been described [96]. Insulin therapy is mandatory,
however, it should be accompanied by a complex involvement
of ophtalmologists, nephrologists, otolaryngologists
and neurologists. Life-span is shortened [97].
Immunodysregulation polyendocrinopathy enteropathy
X-linked (IPEX) syndrome is caused by mutations of
the fork-head box protein 3 (FOXP3) gene located on the
short arm of the X chromosome (Xp11.23). It encodes
FOXP3 protein that is crucial for the function of regulatory
T-cells, thus the diabetes is of an autoimmune nature
and general disorder of immunity. More than 70 different
mutations have been described. The most common mutation
is the substitution of the Pro339 by alanine or other
amino acids [98]. Clinical presentation involves enteropathy,
autoimmune diabetes, immunodeficiency, severe
infections; 65.0% of patients survive. Treatment with immunosuppressive
agents is recommended [99].
Utility of Testing for Neonatal Diabetes. Having
in mind all previously mentioned forms of PNDM, and
many others that are extremely rare, there is a reasonable
algorithm of testing that should be performed when NDM
occurs. The first approach is to test for 6q24 abnormalities
which cause 68.0% of TNDM. If it is negative, further
testing for the KCNJ11 gene should follow (10.0% of
patients with NDM carry it), and if it is normal, tests for
ABCC8 gene mutations should be performed, as they
are the cause of ND in 9.0% of patients. Novel methods
provide simultaneous testing for many genes involved
in monogenic diabetes including both NDM and MODY.
Targeted NGS has been successfully applied [26] as well
as the combination of NGS and methylation-specific
multiplex ligation-dependent probe amplification (MSMLPA),
assay for the detection of both transient and
permanent NDM [100].
Molecular diagnosis of NDM is of the utmost importance
as it provides the appropriate selection of therapy
[77-79], which is in concordance with precision medicine
[101]. It is also economically valuable as it provides the
opportunity for transfer to oral therapy in certain patients
[102,103], improving the QoL, and decreasing the cost of
treatment [104]. On the other hand, knowing the molecular
mechanisms of hyperglycemia provides new research for
novel therapies [105], and gives insight into the mechanisms
of more common forms of diabetes [106].
Conclusions. Neonatal diabetes is monogenic, and
genetically polymorphic. Due to the severity of onset, danger
of an unfavorable outcome and uncertain future, NDM
should be genetically characterized as soon as possible
through international platforms for countries with funding
problems for genetic testing. The importance of this testing
is providing a precise diagnosis, precision medicine,
individual therapy and best possible outcome. However,
genetic diagnosis has also taught endocrinologists of many
physiological pathways in the β-cell function, genetic control
of glucose homeostasis and interplay of involved genes
in control of other organs.
Declaration of Interest. The authors report no conflicts
of interest. The authors alone are responsible for the
content and writing of this article.
|
|
|
|
 |
Number 27
VOL. 27 (2), 2024 |
Number 27
VOL. 27 (1), 2024 |
Number 26
Number 26 VOL. 26(2), 2023 All in one |
Number 26
VOL. 26(2), 2023 |
Number 26
VOL. 26, 2023 Supplement |
Number 26
VOL. 26(1), 2023 |
Number 25
VOL. 25(2), 2022 |
Number 25
VOL. 25 (1), 2022 |
Number 24
VOL. 24(2), 2021 |
Number 24
VOL. 24(1), 2021 |
Number 23
VOL. 23(2), 2020 |
Number 22
VOL. 22(2), 2019 |
Number 22
VOL. 22(1), 2019 |
Number 22
VOL. 22, 2019 Supplement |
Number 21
VOL. 21(2), 2018 |
Number 21
VOL. 21 (1), 2018 |
Number 21
VOL. 21, 2018 Supplement |
Number 20
VOL. 20 (2), 2017 |
Number 20
VOL. 20 (1), 2017 |
Number 19
VOL. 19 (2), 2016 |
Number 19
VOL. 19 (1), 2016 |
Number 18
VOL. 18 (2), 2015 |
Number 18
VOL. 18 (1), 2015 |
Number 17
VOL. 17 (2), 2014 |
Number 17
VOL. 17 (1), 2014 |
Number 16
VOL. 16 (2), 2013 |
Number 16
VOL. 16 (1), 2013 |
Number 15
VOL. 15 (2), 2012 |
Number 15
VOL. 15, 2012 Supplement |
Number 15
Vol. 15 (1), 2012 |
Number 14
14 - Vol. 14 (2), 2011 |
Number 14
The 9th Balkan Congress of Medical Genetics |
Number 14
14 - Vol. 14 (1), 2011 |
Number 13
Vol. 13 (2), 2010 |
Number 13
Vol.13 (1), 2010 |
Number 12
Vol.12 (2), 2009 |
Number 12
Vol.12 (1), 2009 |
Number 11
Vol.11 (2),2008 |
Number 11
Vol.11 (1),2008 |
Number 10
Vol.10 (2), 2007 |
Number 10
10 (1),2007 |
Number 9
1&2, 2006 |
Number 9
3&4, 2006 |
Number 8
1&2, 2005 |
Number 8
3&4, 2004 |
Number 7
1&2, 2004 |
Number 6
3&4, 2003 |
Number 6
1&2, 2003 |
Number 5
3&4, 2002 |
Number 5
1&2, 2002 |
Number 4
Vol.3 (4), 2000 |
Number 4
Vol.2 (4), 1999 |
Number 4
Vol.1 (4), 1998 |
Number 4
3&4, 2001 |
Number 4
1&2, 2001 |
Number 3
Vol.3 (3), 2000 |
Number 3
Vol.2 (3), 1999 |
Number 3
Vol.1 (3), 1998 |
Number 2
Vol.3(2), 2000 |
Number 2
Vol.1 (2), 1998 |
Number 2
Vol.2 (2), 1999 |
Number 1
Vol.3 (1), 2000 |
Number 1
Vol.2 (1), 1999 |
Number 1
Vol.1 (1), 1998 |
|
|
