Neonatal diabetes mellitus (NDM) and congenital hyperinsulinism (CH) are complementary disorders of defective insulin secretion that typically affect the newborn and young infant. The biological defect common to both conditions and causing the majority of cases is in the ATP-sensitive potassium (K_ATP) channel of the pancreatic islet beta cell. This channel is responsible for triggering insulin release in response to increased glucose levels. The ABCC8 and KCNJ11 genes encode respectively the SUR1 and Kir6.2 subunits of the channel; activating mutations in either gene can cause NDM, and inactivating mutations can cause CH. The glucokinase gene, GCK, regulates the first step of glucose metabolism and mutations in this gene may also result in either condition. In addition, mutations in the insulin gene INS have been shown to cause neonatal diabetes.

The Ambry SEQUENCE is a cost-saving pathway for diagnosing diseases that may be caused by mutations in any of several genes, such as neonatal diabetes and congenital hyperinsulinism. By starting with the most common genetic cause and reflexing through analyses of less commonly responsible genes, unnecessary testing is avoided. SEQUENCE pathways for each condition are described below. In addition, testing may be ordered for single genes or for concurrent testing of any combination of genes. Tests offered for all five genes (ABCC8, KCNJ11, INS, GCK, and IPF1) are full gene sequence analyses with mutation detection rates of approximately 99%.

Neonatal diabetes mellitus (NDM) presents in the first six months of life and is characterized by intrauterine growth restriction, failure to thrive, diabetic ketoacidosis, low levels of insulin, and the absence of diabetes antibodies. The condition is considered under-recognized, with incidence estimates ranging from 1/500,000 to 1/100,000 newborns. NDM is further classified as transient (TNDM) or permanent (PNDM). TNDM is primarily caused by abnormal expression of genes at chromosome 6q24 due to epigenetic factors rather than gene mutations.

Mutations in four genes account for a majority of PNDM cases.  Most frequently mutations are found in KCNJ11, accounting for 30-58% of cases.  Mutations in INS have been shown to cause approximately 12% of cases with ABCC8 mutations causing another 10%.  Mutations in KCNJ11 or ABCC8 may result in TNDM or DEND syndrome, which is characterized in its most severe form by developmental delay and generalized epilepsy in addition to neonatal diabetes.  Neurological deficits are not known to be associated with insulin mutations.  PNDM caused by mutations in GCK (about 4% of patients) will be insulin-dependent.  IPF1 mutations, a rare cause, result in partial or complete pancreatic agenesis which requires treatment with insulin.

Determination of the genetic etiology of neonatal diabetes matters for:

• Supervision for possible relapse in childhood or adolescence in the case of TNDM.
• Appropriate management of PNDM. Recent studies reveal up to 90% of KCNJ11- or ABCC8-related diabetes can be successfully treated with sulfonylurea oral medications rather than insulin.
• Genetic counseling for parents and family members.

Negative family history is not a good indicator of whether the patient’s diabetes is genetic as a large proprortion of KCNJ11, INS and ABCC8 mutations are spontaneous and GCK and IPF1 mutations are recessively inherited.

The Ambry SEQUENCE: Neonatal Diabetes begins with full gene analysis of KCNJ11, which is mutated in 30-58% of patients.  Patients who are negative for KCNJ11 mutations are then automatically tested for INS which yields a genetic diagnosis in another 12% of cases. If no INS mutation is detected, ABCC8 testing follows for overall molecular diagnostic confirmation in up to 80% of patients.

GCK testing may be added to the SEQUENCE at the physician’s discretion, with another 4% of cases positive for mutations.  Also, testing is available separately or in any combination for the five relevant genes KCNJ11, INS, ABCC8, GCK, and IPF1.

Congenital hyperinsulinism (CH) has been diagnosed in most ethnicities, and its frequency is approximately 1/50,000 in Europeans. Excessive insulin secretion in these patients results in hypoglycemia. Presentation varies from severe neonatal onset with seizures and hypotonia through mild episodes later in infancy or early childhood. Congenital hyperinsulinism occurs in a diffuse form, generalized throughout the pancreas, which may be treated with pancreatic resection, and a focal form, limited to a single or small number of hyperplastic areas of the pancreas which can be targeted for selective surgical removal.

Inactivating mutations of ABCC8 and KCNJ11 cause approximately 45% and 5% of CH cases respectively. In rare cases, the condition is caused by GCK mutations.

Genetic analysis in CH is useful for:

• Appropriate clinical management. Most ABCC8- and KCNJ11-related hyperinsulinism does not respond well to diazoxide treatment. However, cases caused by GCK mutations may be treatable with this type of drug.
• Genetic counseling for parents and family members.

Although this condition is also called Familial Hyperinsulinism of Infancy (FHI), family history negative for dysfunctional insulin/glucose regulation is not a good indicator of whether the patient’s congenital hyperinsulinism is genetic. The majority of KCNJ11 and ABCC8 mutations in this condition are recessively inherited and others are spontaneous.

The Ambry SEQUENCE: Congenital Hyperinsulinism begins with full gene analysis of ABCC8, which is mutated in approximately 45% of patients. Patients who are negative for ABCC8 mutations are then automatically tested for KCNJ11 which yields a genetic diagnosis in another 5% of cases for overall molecular diagnostic confirmation in up to 50% of patients.

GCK testing may be added to the SEQUENCE at the physician’s discretion. Also, testing is available separately or in any combination for the three relevant genes ABCC8, KCNJ11, and GCK.

    General Test Information
The Ambry Test: ABCC8-Related Diabetes
    (Abobe PDF document)

    General Test Information
The Ambry Test: GCK-Related Diabetes
    (Abobe PDF document)

    General Test Information
The Ambry Test: INS-Related Diabetes
    (Abobe PDF document)

    General Test Information
The Ambry Test: IPF1-Related Diabetes
    (Abobe PDF document)

    General Test Information
The Ambry Test: KCNJ11-Related Diabetes
    (Abobe PDF document)

The following CPT Codes for The Ambry Test reflect Ambry Genetics’ interpretation of CPT coding requirements based on AMA guidelines:

Ambry SEQUENCE: Neonatal Diabetes
83891, 83894, 83898, 83904, 83909, 83912

Ambry SEQUENCE: Congenital Hyperinsulinism
83891, 83894, 83898, 83904, 83909, 83912

Ambry Test: ABCC8-Related Diabetes
83891, 83894, 83898, 83904, 83909, 83912

Ambry Test: GCK-Related Diabetes
83891, 83894, 83898, 83904, 83909, 83912

Ambry Test: INS-Related Diabetes
83891, 83894, 83898, 83904, 83909, 83912

Ambry Test: IPF1-Related Diabetes
83891, 83894, 83898, 83904, 83909, 83912

Ambry Test: KCNJ11-Related Diabetes
83891, 83894, 83898, 83904, 83909, 83912

Disclaimer:

This test was developed and its performance characteristics were determined by Ambry Genetics Corporation. The laboratory is regulated under the Clinical Laboratory Improvement Amendments 2003 as qualified to perform nonwaived testing.  The Ambry Tests described above analyze the following types of mutations: nucleotide substitutions, small deletions, small insertions, and small indels.  They are not intended to analyze the following types of mutations: gross insertions, gross rearrangements, deep intronic variations, and other unknown abnormalities.  The pattern of mutation types varies with the gene tested and the Ambry Test detects a high but variable percentage of known and unknown mutants of the classes stated.  A negative result from the analysis cannot rule out the possibility that the tested individual carries a rare unexamined mutation or mutation in the undetectable group.  The Ambry Tests described above are designed and validated to be capable of detecting about ~99% of mutations in the genes listed (considering less than 1% to be the other types of mutations).  Diabetes is a complex clinical disorder, which in some cases is due to alterations in the genes listed generally detected by the Ambry Test except as noted above.  Mutations in other genes or the regions not tested by the Ambry Test, or disease processes not yet related to genetics, can also give rise to clinical conditions similar or identical to neonatal diabetes or congenital hyperinsulinism.  Although molecular tests are highly accurate, rare diagnostic errors may occur.  Possible diagnostic errors include sample mix-up, erroneous paternity identification, technical errors, clerical errors, and genotyping errors. Genotyping errors can result from trace contamination of PCR reactions, from maternal cell contamination in fetal samples, from rare genetic variants, which interfere with analysis, or from other sources.  Reports do not represent medical advice. Any questions, suggestions, or concerns regarding interpretation of results should be forwarded to a genetic counselor, medical geneticist, or physician skilled in interpretation of the relevant medical literature. References are available upon request.