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What is Maturity-onset diabetes of the young and explain in detail?
Maturity-onset diabetes of the young (MODY) refers to any of several hereditary forms of diabetes mellitus caused by mutations in an autosomal dominant gene disrupting insulin production. MODY is often referred to as monogenic diabetes to distinguish it from the more common types of diabetes (especially type 1 and type 2), which involve more complex combinations of causes involving multiple genes and environmental factors. MODY 2 and MODY 3 are the most common forms.Robert Tattersall and Stefan Fajans initially identified the phenomenon known as maturity onset diabetes of the young in a classic study published in the journal Diabetes in 1975.

Signs and symptoms
MODY is the final diagnosis in 1%–2% of people initially diagnosed with diabetes. The prevalence is 70–110 per million people. 50% of first-degree relatives will inherit the same mutation, giving them a greater than 95% lifetime risk of developing MODY themselves. For this reason, correct diagnosis of this condition is important. Typically patients present with a strong family history of diabetes (any type) and the onset of symptoms is in the second to fifth decade.
There are two general types of clinical presentation.

Some forms of MODY produce significant hyperglycemia and the typical signs and symptoms of diabetes: increased thirst and urination (polydipsia and polyuria).
In contrast, many people with MODY have no signs or symptoms and are diagnosed either by accident, when a high glucose is discovered during testing for other reasons, or screening of relatives of a person discovered to have diabetes. Discovery of mild hyperglycemia during a routine glucose tolerance test for pregnancy is particularly characteristic.MODY cases may make up as many as 5% of presumed type 1 and type 2 diabetes cases in a large clinic population. While the goals of diabetes management are the same no matter what type, there are two primary advantages of confirming a diagnosis of MODY.

Insulin may not be necessary and it may be possible to switch a person from insulin injections to oral agents without loss of glycemic control.
It may prompt screening of relatives and so help identify other cases in family members.As it occurs infrequently, many cases of MODY are initially assumed to be more common forms of diabetes: type 1 if the patient is young and not overweight, type 2 if the patient is overweight, or gestational diabetes if the patient is pregnant. Standard diabetes treatments (insulin for type 1 and gestational diabetes, and oral hypoglycemic agents for type 2) are often initiated before the doctor suspects a more unusual form of diabetes.

Genetics
Some sources make a distinction between two forms of monogenetic diabetes: MODY and neonatal diabetes. However, they have much in common and are often studied together.

Heterozygous
MODY is inherited in an autosomal dominant fashion, and most patients therefore have other members of the family with diabetes; penetrance differs between the types (from 40% to 90%).

Homozygous
By definition, the forms of MODY are autosomal dominant, requiring only one abnormal gene to produce the disease; the severity of the disease is moderated by the presence of a second, normal allele which presumably functions normally. However, conditions involving people carrying two abnormal alleles have been identified. Unsurprisingly, combined (homozygous) defects of these genes are much rarer and much more severe in their effects.

MODY2: Homozygous glucokinase deficiency causes severe congenital insulin deficiency resulting in persistent neonatal diabetes mellitus. About 6 cases have been reported worldwide. All have required insulin treatment from shortly after birth. The condition does not seem to improve with age.
MODY4: Homozygous IPF1 results in failure of the pancreas to form. Congenital absence of the pancreas, termed pancreatic agenesis, involves deficiency of both endocrine and exocrine functions of the pancreas.Homozygous mutations in the other forms have not yet been described. Those mutations for which a homozygous form has not been described may be extremely rare, may result in clinical problems not yet recognized as connected to the monogenic disorder, or may be lethal for a fetus and not result in a viable child.

Pathophysiology
The recognised forms of MODY are all due to ineffective insulin production or release by pancreatic beta cells. Several of the defects are mutations of transcription factor genes. One form is due to mutations of the glucokinase gene. For each form of MODY, multiple specific mutations involving different amino acid substitutions have been discovered. In some cases, there are significant differences in the activity of the mutant gene product that contribute to variations in the clinical features of the diabetes (such as degree of insulin deficiency or age of onset).

Diagnosis
The following characteristics suggest the possibility of a diagnosis of MODY in hyperglycemic and diabetic patients:
Mild to moderate hyperglycemia (typically 130–250 mg/dL, or 7–14 mmol/L) discovered before 30 years of age. However, anyone under 50 can develop MODY.
A first-degree relative with a similar degree of diabetes.
Absence of positive antibodies or other autoimmunity (e.g., thyroiditis) in patient and family. However, Urbanova et al. found that about one quarter of Central European MODY patients are positive for islet cell autoantibodies (GABA and IA2A). Their expression is transient but highly prevalent. The autoantibodies were found in patients with delayed diabetes onset, and in times of insufficient diabetes control. The islet cell autoantibodies are absent in MODY in at least some populations (Japanese, Britons).
Persistence of a low insulin requirement (e.g., less than 0.5 u/kg/day) past the usual "honeymoon" period.
Absence of obesity (although overweight or obese people can get MODY) or other problems associated with type 2 diabetes or metabolic syndrome (e.g., hypertension, hyperlipidemia, polycystic ovary syndrome).
Insulin resistance very rarely happens.
Cystic kidney disease in patient or close relatives.
Non-transient neonatal diabetes, or apparent type 1 diabetes with onset before six months of age.
Liver adenoma or hepatocellular carcinoma in MODY type 3
Renal cysts, rudimentary or bicornuate uterus, vaginal aplasia, absence of the vas deferens, epidymal cysts in MODY type 5The diagnosis of MODY is confirmed by specific gene testing available through commercial laboratories.

Classification
Common or well-established forms of MODY (1% of MODY or greater) - HNF1A-(MODY3), HNF4A-(MODY1) and GCK-(MODY2), HNF1B-(MODY5), ABCC8-(MODY12), KCNJ11-(MODY13), INS-(MODY10)
Rare forms of MODY (Few families described but reasonable generic evidence for causing MODY) - NEUROD1-(MODY6), IPF1/PDX1-(MODY4), CEL-(MODY8), WSF1 and RFX6
Genes reported as causal for MODY but evidence not compelling - BLK-(MODY11), PAX4-(MODY9) and KLF11-(MODY7), APPL1-(MODY14), NKX6-1

Treatment
In some forms of MODY, standard treatment is appropriate, though exceptions occur:

In MODY2, oral agents are relatively ineffective, however most patients are managed conservatively through diet and exercise.
In MODY1 and MODY3, sulfonylureas are usually very effective, delaying the need for insulin treatment.
Sulfonylureas are effective in the KATP channel forms of neonatal-onset diabetes. The mouse model of MODY diabetes suggested that the reduced clearance of sulfonylureas stands behind their therapeutic success in human MODY patients, but Urbanova et al