Diabetes Mellitus (Type 1)

Summary / Overview

Autoimmune destruction of pancreatic β-cells → absolute insulin deficiency.
Occurs mainly in children & adolescents but can appear at any age (LADA in adults).
• Caused by immune-mediated attack against β-cells (HLA-linked).
• Progressive loss of insulin production → hyperglycemia, ketosis, weight loss.
• Often presents acutely with polyuria, polydipsia, dehydration, and fatigue.
• Requires lifelong insulin therapy for survival.

Etiology

Type 1 diabetes is an autoimmune destruction of pancreatic β-cells leading to absolute insulin deficiency.
• Peak onset in childhood and adolescence, but can occur at any age.
• Autoimmune process mediated mainly by T-cells → gradual β-cell loss before symptoms appear.
• Genetic susceptibility strongly associated with HLA-DR3, DR4, DQ2, DQ8.
• Environmental triggers (viral infections, dietary factors) initiate autoimmune cascade.
• Symptoms appear when ~80–90% of β-cells are destroyed.
• Presents acutely with hyperglycemia, polyuria, polydipsia, weight loss, fatigue.
• High risk of diabetic ketoacidosis (DKA) at presentation.
• Autoimmune markers: GAD65, IA-2, ZnT8, IAA positive in majority.

Pathogenesis

Autoimmune destruction of pancreatic β-cells
• Strong association with HLA-DR3, DR4, DQ2, DQ8.
• Risk increases if a first-degree relative is affected.
Molecular mechanism
• Autoantibodies form against β-cell antigens → serve as markers of ongoing immune destruction.
• Anti-GAD (glutamic acid decarboxylase).

Symptoms

Blurred vision
Nocturia
Recurrent infections
Symptoms of ketoacidosis
• Abdominal pain.
• Nausea/vomiting.

Signs

Classic triad: polydipsia, polyuria, weight loss
• Dehydration (dry mucous membranes, poor skin turgor)
• Tachycardia
• Hypotension (in moderate–severe cases)
• Smell of ketones on breath (fruity odor)
• Kussmaul breathing (deep, rapid respiration)
• Reduced subcutaneous fat and muscle wasting
• Abdominal tenderness (may suggest DKA)
• Signs of associated autoimmune disease (vitiligo, thyroid enlargement)

Clinical Features

Polydipsia – excessive thirst due to hyperosmolar serum.
Polyuria – osmotic diuresis from glucosuria.
Polyphagia – cellular starvation despite hyperglycemia.
Unintentional weight loss – fat and muscle catabolism due to insulin deficiency.
• Fatigue and malaise
• Blurred vision
• Nocturia
• Recurrent infections (skin, urinary, candida)

Investigations

Diagnosis requires confirmation of hyperglycemia + autoimmune markers.
• Fasting plasma glucose ≥126 mg/dL on two occasions.
• Random plasma glucose ≥200 mg/dL with classic symptoms (polyuria, polydipsia, weight loss).
• Oral Glucose Tolerance Test (OGTT): 2-hour value ≥200 mg/dL.
• HbA1c ≥6.5% → supports diagnosis (if lab-standardized).
• Urine ketones → positive in most newly diagnosed patients.
• Autoantibody panel (confirm autoimmune destruction):
– GAD65 antibodies
• Celiac disease screening (tTG-IgA) → common autoimmune comorbidity.

Differential Diagnosis

No key-points marked yet. Add lines like *Important point* in this section.

Complications

Diabetic Ketoacidosis (DKA) — acute, life-threatening insulin deficiency → hyperglycemia, ketonemia, acidosis.
• Severe dehydration due to osmotic diuresis
• Kussmaul breathing
Acute complications
• Hypoglycemia (due to excess insulin, missed meals, exercise mismatch)
• Hyperglycemia / ketosis in illness or insulin omission
Chronic microvascular complications
• Diabetic retinopathy → non-proliferative → proliferative
• Diabetic nephropathy → microalbuminuria → proteinuria → renal failure
• Diabetic neuropathy → distal symmetric polyneuropathy, autonomic neuropathy

Treatment

Lifelong insulin therapy (mandatory)
• Absolute insulin deficiency → patient cannot survive without insulin.
• Multiple daily injections (MDI) OR insulin pump therapy.
• Basal insulin: long-acting (glargine, detemir, degludec).
• Bolus insulin: rapid-acting before meals (aspart, lispro, glulisine).
• Dose based on carbohydrate counting ± correction factor.
Insulin pump therapy improves glycemic control
• Delivers continuous basal infusion + meal boluses.
• Useful for children, adolescents, and patients with hypoglycemia unawareness.
Continuous Glucose Monitoring (CGM)

Prevention

Primary autoimmune prevention is currently not possible
Teplizumab (anti-CD3) can delay progression in high-risk individuals
Managing co-existing autoimmune triggers may delay β-cell loss
Environmental factor modification remains theoretical
Once T1DM develops, prevent further β-cell loss
Long-term prevention focuses on complications

Serotypes / Subtypes

No key-points marked yet. Add lines like *Important point* in this section.

Pathology

Autoimmune destruction of pancreatic β-cells is the core pathology.
• Chronic immune-mediated injury directed against insulin-producing β-cells.
• CD4+ and CD8+ T-cell infiltration of pancreatic islets → “insulitis.”
• Progressive loss of β-cell mass leads to absolute insulin deficiency.
• Early phase: patchy inflammation; late phase: near-total β-cell depletion.
• α-cells (glucagon-producing) are relatively preserved.
• Residual β-cells may persist temporarily (“honeymoon period”).
• Autoantibodies indicate immune activity, not direct destruction.
• Marked reduction in islet size and number on histology.
• Hyperglycemia → osmotic diuresis, dehydration, electrolyte imbalance.

Notes / Teaching points

Why is Type 1 DM called “autoimmune β-cell destruction”?
Which antibodies are typically present in early Type 1 DM?
Why do children present suddenly with polyuria and weight loss?
Why do some patients present with DKA first?
Why is C-peptide low in Type 1 DM?
Can Type 1 DM be prevented?
Why honeymoon phase occurs?
What differentiates LADA from classic Type 1 DM?
Why insulin is lifelong necessity?
What is the most dangerous complication?

Other

Early prevention (on going development)
Type 1 Diabetes is driven by autoimmune destruction of pancreatic β-cells, mainly mediated by:
• Autoantibodies (GAD65, IA-2, ZnT8, IAA)
• Autoreactive CD4+ and CD8+ T-cells (dominant mechanism)
So the core pathology is T-cell–driven, not primarily antibody driven.
However, research and some approved treatments can slow progression, especially in early stages (Stage 1 & 2 T1D).
Teplizumab (Anti-CD3 monoclonal antibody)(FDA)

Diabetic Ketoacidosis (DKA) — acute, life-threatening insulin deficiency → hyperglycemia, ketonemia, acidosis.

• Severe dehydration due to osmotic diuresis

• Kussmaul breathing

• Abdominal pain, vomiting

• Altered sensorium in severe cases

Acute complications

• Hypoglycemia (due to excess insulin, missed meals, exercise mismatch)

• Hyperglycemia / ketosis in illness or insulin omission

Chronic microvascular complications

• Diabetic retinopathy → non-proliferative → proliferative

• Diabetic nephropathy → microalbuminuria → proteinuria → renal failure

• Diabetic neuropathy → distal symmetric polyneuropathy, autonomic neuropathy

• Diabetic foot ulcers due to neuropathy + ischemia

Chronic macrovascular complications

• Coronary artery disease

• Stroke (CVA)

• Peripheral arterial disease

Autonomic dysfunction

• Gastroparesis

• Orthostatic hypotension

• Bladder dysfunction

• Erectile dysfunction

*Skeletal & growth effects in children*Dr

• Poor growth and delayed puberty if glycemic control is poor

Infections

• Increased susceptibility to skin, urinary, and fungal infections

Complications from poor control

• Weight loss, muscle wasting

• Electrolyte abnormalities

• Recurrent hospitalizations

• Type 2 diabetes mellitus (T2DM) — gradual onset, obesity, insulin resistance predominant

• Latent autoimmune diabetes in adults (LADA) — adult onset, slower β-cell loss, positive antibodies

• Maturity-onset diabetes of the young (MODY) — non-ketotic, strong family history, monogenic

• Secondary diabetes (pancreatic destruction) — chronic pancreatitis, pancreatic surgery, cystic fibrosis

• Steroid-induced diabetes

• Stress hyperglycemia (acute illness, sepsis, trauma)

• Ketosis-prone type 2 diabetes (“Flatbush diabetes”)

• Hyperthyroidism with hyperglycemia

• Cushing syndrome / acromegaly / pheochromocytoma

• Drug-induced hyperglycemia (thiazides, antipsychotics, tacrolimus)

• Classic DKA presenting from other causes:

– Alcoholic ketoacidosis

– Starvation ketoacidosis

– Euglycemic DKA (SGLT2 inhibitors)

Type 1 diabetes is an autoimmune destruction of pancreatic β-cells leading to absolute insulin deficiency.

• Peak onset in childhood and adolescence, but can occur at any age.

• Autoimmune process mediated mainly by T-cells → gradual β-cell loss before symptoms appear.

• Genetic susceptibility strongly associated with HLA-DR3, DR4, DQ2, DQ8.

• Environmental triggers (viral infections, dietary factors) initiate autoimmune cascade.

• Symptoms appear when ~80–90% of β-cells are destroyed.

• Presents acutely with hyperglycemia, polyuria, polydipsia, weight loss, fatigue.

• High risk of diabetic ketoacidosis (DKA) at presentation.

• Lifelong dependence on exogenous insulin for survival.

• Not associated with insulin resistance (unlike Type 2).

• Autoimmune markers: GAD65, IA-2, ZnT8, IAA positive in majority.

• Usually lean body habitus at presentation.

• Rapid progression compared to type 2 diabetes.

Autoimmune destruction of pancreatic β-cells

Type 1 DM results from immune-mediated destruction of insulin-producing β-cells of the pancreas → absolute insulin deficiency.

• T-cell–mediated autoimmune attack on β-cells (main driver).

• Presence of islet autoantibodies: GAD65, IA-2, ZnT8, ICA.

• Loss of β-cells progresses silently for months to years before symptoms.

Genetic susceptibility

• Strong HLA association (HLA-DR3, DR4, DQ2, DQ8).

• Family history increases risk but most patients have no affected relatives.

Environmental triggers

• Viral infections (coxsackievirus B, CMV, enteroviruses).

• Early cow’s milk exposure, low vitamin D (possible links).

• Childhood stressors or immune dysregulation.

Bimodal onset pattern

• Peaks in childhood (4–7 years) and adolescence (10–14 years).

Absolute insulin deficiency

• Clinical presentation occurs only after >80–90% β-cell destruction.

Diagnosis requires confirmation of hyperglycemia + autoimmune markers.

• Fasting plasma glucose ≥126 mg/dL on two occasions.

• Random plasma glucose ≥200 mg/dL with classic symptoms (polyuria, polydipsia, weight loss).

• Oral Glucose Tolerance Test (OGTT): 2-hour value ≥200 mg/dL.

• HbA1c ≥6.5% → supports diagnosis (if lab-standardized).

Hyperglycemia with ketosis in a young patient strongly supports T1DM.

• Urine ketones → positive in most newly diagnosed patients.

• Serum ketones (β-hydroxybutyrate) → elevated in DKA.

• Arterial/venous blood gas → metabolic acidosis assessment.

Early testing prevents progression to diabetic ketoacidosis (DKA).

• Autoantibody panel (confirm autoimmune destruction):

– GAD65 antibodies

*– IA-2 antibodies*

*– ZnT8 antibodies*

*– Islet cell antibodies (ICA)*

Positive autoantibodies differentiate Type-1 from Type-2 diabetes.

• C-peptide level → low or absent.

Low C-peptide = low endogenous insulin production.

• Electrolytes (Na⁺, K⁺, Cl⁻, HCO₃⁻) → for DKA evaluation.

• Renal function test (creatinine, BUN).

• Serum osmolality (if severe hyperglycemia).

• Complete blood count (rule out infection triggering DKA).

• Thyroid function tests (TSH, T4) → due to high association with autoimmune thyroid disease.

• Celiac disease screening (tTG-IgA) → common autoimmune comorbidity.

Why is Type 1 DM called “autoimmune β-cell destruction”?

Because autoreactive T-cells target pancreatic β-cells → progressive loss of insulin production → absolute insulin deficiency.

Which antibodies are typically present in early Type 1 DM?

• GAD65 antibodies

• IA-2 antibodies

• ZnT8 antibodies

• Insulin autoantibodies (IAA)

Their presence predicts β-cell failure but does not always cause symptoms immediately.

Why do children present suddenly with polyuria and weight loss?

Insulin deficiency develops slowly, but symptoms appear only when ~80–90% β-cells are destroyed → sudden unmasking of hyperglycemia.

Why do some patients present with DKA first?

Absolute insulin deficiency → unchecked lipolysis → ketone overproduction → metabolic acidosis.

Why is C-peptide low in Type 1 DM?

Because endogenous insulin production is minimal; injected insulin does not contain C-peptide.

Can Type 1 DM be prevented?

Currently no proven therapy prevents autoimmune β-cell destruction.

Trials with anti-CD3, anti-CD20, and oral insulin show partial delay but not full prevention.

Why honeymoon phase occurs?

After insulin initiation, glucose toxicity decreases → remaining β-cells regain temporary function → short period of low insulin requirement.

What differentiates LADA from classic Type 1 DM?

LADA presents in adults, slower β-cell destruction, still antibody-positive, but no acute DKA at onset.

Why insulin is lifelong necessity?

Because pancreatic β-cells are permanently destroyed and cannot regenerate sufficiently.

What is the most dangerous complication?

Diabetic ketoacidosis (DKA) → risk increases during infections, missed insulin doses, or dehydration.

Early prevention (on going development)

Type 1 Diabetes is driven by autoimmune destruction of pancreatic β-cells, mainly mediated by:

• Autoantibodies (GAD65, IA-2, ZnT8, IAA)

• Autoreactive CD4+ and CD8+ T-cells (dominant mechanism)

So the core pathology is T-cell–driven, not primarily antibody driven.

However, research and some approved treatments can slow progression, especially in early stages (Stage 1 & 2 T1D).

Teplizumab (Anti-CD3 monoclonal antibody)(FDA)

• First and only drug that delays onset of clinical Type 1 diabetes by ~2–3 years.

• Works by modifying autoreactive T-cells, inducing regulatory T-cells.

• Effective only in early presymptomatic stage (Stage 2).

✔ Can preserve remaining β-cell function temporarily

✔ Does not stop the autoimmune process permanently

✖ Not a cure

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Rituximab (Anti-CD20 monoclonal antibody – targets B-cells)

• Has shown benefit in slowing early β-cell loss.

• Removes B-cells that present autoantigens to T-cells.

• Effect is temporary, β-cell decline continues after 2–3 years.

Used in trials; not yet standard therapy for T1D.

------------

Abatacept (CTLA-4 fusion protein)

• Blocks T-cell co-stimulation.

• Trials show:

• Slowed C-peptide decline in newly diagnosed T1D.

• Partial preservation of β-cell function.

Still investigational.

-------

Low-dose anti-thymocyte globulin (ATG)

• Reduces autoreactive T-cell clones.

• Trials show partial β-cell preservation in new-onset T1D.

-----------

mmunomodulation in children with autoantibodies (research phase)

Strategies under study:

• Oral insulin (immune tolerance induction)

• GAD65 alum vaccine

• Low-dose IL-2 (boosts regulatory T-cells)

• Vitamin D + omega-3 anti-inflammatory protocols

Effect: Modest, not currently disease-modifying.

----------------

🔬 1. Antigen-specific tolerance therapy

Targeted suppression of the anti-GAD, anti-IA-2, anti-ZnT8 responses.

🔬 2. Regulatory T-cell (Treg) therapy

Expand or infuse patient’s own Tregs to silence the autoimmune attack.

🔬 3. β-cell regeneration + immunoprotection

Regenerating β-cells alone is useless unless the immune attack is fixed.

🔬 4. Encapsulated islet transplantation

Islet cells in an immunoprotective capsule → no rejection, no autoimmune attack.

Autoimmune destruction of pancreatic β-cells

• T-cell–mediated immune attack against insulin-producing β-cells.

• Leads to absolute insulin deficiency.

Role of genetic susceptibility

• Strong association with HLA-DR3, DR4, DQ2, DQ8.

• Risk increases if a first-degree relative is affected.

Environmental triggers

• Viral infections (enteroviruses, Coxsackie B).

• Early exposure to cow-milk proteins (possible weak association).

• Childhood stressors / immune activation.

Molecular mechanism

• Autoantibodies form against β-cell antigens → serve as markers of ongoing immune destruction.

• Progressive β-cell apoptosis occurs before symptoms begin.

Major autoantibodies

• Anti-GAD (glutamic acid decarboxylase).

• Anti-IA2 (insulinoma-associated antigen).

• Anti-ZnT8 (zinc transporter).

• Anti-insulin antibodies (IAA).

“Honeymoon phase”

• Shortly after diagnosis, some residual β-cells temporarily produce insulin.

• Leads to transient partial remission → then complete failure.

Ketoacidosis pathway

• Absolute insulin deficiency → uninhibited lipolysis → excess ketone production → metabolic acidosis.

Primary autoimmune prevention is currently not possible

The autoimmune destruction of β-cells cannot be reliably prevented at population level.

• Genetic risk cannot be modified (HLA-DR3, DR4, DQ2, DQ8 increase susceptibility).

• Avoidance of cow’s milk early in infancy **does not** prevent T1DM (large trials negative).

• Vitamin D supplementation shows association but **not proven** to prevent disease.

Teplizumab (anti-CD3) can delay progression in high-risk individuals

Used in relatives with abnormal autoantibodies + dysglycemia → delays onset by ~2 years.

• Screening of first-degree relatives for islet autoantibodies (research settings).

• Early detection of stage 2 (autoantibodies + glucose abnormality) may allow immunotherapy.

Managing co-existing autoimmune triggers may delay β-cell loss

• Treat autoimmune thyroiditis, celiac disease early.

• Reduce chronic inflammatory burden where possible.

Environmental factor modification remains theoretical

• Viral trigger reduction (enterovirus vaccines under research).

• Gut microbiome modulation (no proven recommendations yet).

Once T1DM develops, prevent further β-cell loss

• Early intensive insulin therapy preserves “honeymoon phase.”

• Maintain near-normal glucose → reduces glucotoxicity on remaining β-cell function.

Long-term prevention focuses on complications

• Tight glycemic control.

• BP control, lipid control.

• Annual eye, kidney, nerve screening.

• Lifestyle: diet, exercise, avoid smoking.

Type-1 DM has several immunological and clinical subtypes based on autoimmunity, β-cell destruction speed, and genetic features.

• Type 1A — Autoimmune-mediated β-cell destruction

– Most common form.

– Presence of islet autoantibodies (GAD65, IA-2, ZnT8, IAA).

– Strong HLA association (DR3, DR4, DQ2, DQ8).

• Type 1B — Idiopathic (antibody-negative)

– No detectable autoantibodies.

– Episodic ketoacidosis.

– More common in African and Asian populations.

• Fulminant Type-1 Diabetes

– Very rapid β-cell destruction.

– Severe DKA at presentation despite short symptom duration.

– Often associated with viral triggers.

• Latent Autoimmune Diabetes in Adults (LADA) — “slow-onset type 1”

– Adults >30 years.

– Positive for GAD or other antibodies.

– Initially insulin-independent, later progresses to insulin requirement.

– Often misdiagnosed as type 2 DM.

• MODY vs Type-1 DM — NOT a subtype but an important distinction

– Monogenic diabetes with preserved β-cell function.

– No autoimmunity.

– Helps avoid misclassification.

• INS-gene mutation / monogenic autoimmunity-related diabetes

– Very rare.

– Leads to neonatal or early infantile diabetes.

– Not true type-1, but clinically important to separate.

• Stages of Autoimmune Type-1 DM (useful subclassification)

Stage 1: Normoglycemia + islet autoantibodies

Stage 2: Dysglycemia + antibodies

Stage 3: Symptomatic hyperglycemia (clinical diabetes)

Classic symptom triad

• Polyuria — excessive urination due to osmotic diuresis.

• Polydipsia — intense thirst.

• Polyphagia — increased hunger despite weight loss.

Unintentional weight loss

• Occurs because the body cannot utilize glucose → breaks down fat & muscle.

Fatigue and weakness

• Due to cellular glucose starvation and dehydration.

Blurred vision

• High glucose changes lens shape → transient refractive error.

Nocturia

• Night-time urination due to glucosuria-induced diuresis.

Recurrent infections

• Oral thrush, skin infections, urinary infections more common.

Symptoms of ketoacidosis

• Abdominal pain.

• Nausea/vomiting.

• Deep rapid breathing (Kussmaul respiration).

• Fruity odor on breath (acetone).

• Altered sensorium in severe cases.

Sudden onset in children & adolescents

• Symptoms develop over days–weeks, often dramatic presentation.

Lifelong insulin therapy (mandatory)

• Absolute insulin deficiency → patient cannot survive without insulin.

• Multiple daily injections (MDI) OR insulin pump therapy.

Basal–bolus regimen is the standard of care

• Basal insulin: long-acting (glargine, detemir, degludec).

• Bolus insulin: rapid-acting before meals (aspart, lispro, glulisine).

• Dose based on carbohydrate counting ± correction factor.

Insulin pump therapy improves glycemic control

• Delivers continuous basal infusion + meal boluses.

• Useful for children, adolescents, and patients with hypoglycemia unawareness.

Continuous Glucose Monitoring (CGM)

• Essential for optimizing control.

• Helps detect nocturnal hypoglycemia and glycemic excursions.

• Monitor blood glucose 4–8 times/day if CGM unavailable.

• Target HbA1c <7% (individualized).

• Education on carbohydrate counting.

• Matching insulin dose to carbohydrate intake improves post-meal control.

• Sick-day rules: never stop insulin; monitor glucose + ketones frequently.

• Early detection of diabetic ketoacidosis (DKA).

DKA management is life-saving

• IV fluids, IV insulin infusion, electrolyte correction.

• Identify and treat precipitating factors.

• Annual screening for complications: eyes, kidneys, nerves.

• Foot care education.

• Vaccinations up-to-date.