MAPT and frontotemporal degeneration

What MAPT does

MAPT provides instructions for making tau, a protein that helps organize and stabilize the internal transport system of nerve cells. Tau exists in several forms that are normally kept in balance.

Pathogenic MAPT variants can change tau itself or alter how different forms of tau are produced. Abnormal tau then accumulates in nerve cells and disrupts cell function.

This is a tau-related disease, but it is not the same as Alzheimer's disease. Alzheimer's also contains abnormal tau, together with amyloid, but the molecular forms, regional pattern, and disease context differ. A MAPT result should not be interpreted as a genetic test for Alzheimer's disease.

What symptoms can look like

MAPT-related FTD often begins with progressive changes in behavior, judgment, motivation, empathy, or personality. Some people first develop language or executive difficulties.

Movement symptoms may include stiffness, slowness, tremor, falls, changes in eye movements, or a syndrome resembling parkinsonism, progressive supranuclear palsy, or corticobasal syndrome.

The gene does not determine one single clinical presentation. Symptoms and rate of change can vary, including among relatives. A neurologic examination and the pattern over time remain essential even when a pathogenic variant is known.

How MAPT is inherited

MAPT-related FTD is usually inherited in an autosomal dominant manner. Each child of a person with a pathogenic MAPT variant has a 50 percent chance of inheriting that variant.

Many MAPT pathogenic variants have high penetrance, meaning most carriers eventually develop symptoms. Penetrance and age of onset can still vary by variant and family. A positive result does not provide an exact date or a complete forecast.

A family history may include FTD, psychiatric diagnoses, parkinsonism, language disorders, progressive supranuclear palsy, corticobasal syndrome, or a nonspecific early-onset dementia. Older labels may not capture the relationship among these presentations.

What testing needs to show

The report should identify a pathogenic or likely pathogenic MAPT variant. A variant of uncertain significance does not establish MAPT-related FTD.

Testing often occurs as part of an FTD or dementia multigene panel because the clinical features overlap with GRN, C9orf72, and other causes. C9orf72 repeat analysis may need to be ordered separately if the panel's sequencing method does not detect expansions.

When possible, an affected relative should be tested first. Once a familial MAPT variant is confirmed, unaffected adult relatives can decide whether to pursue targeted predictive testing.

What a positive result can and cannot tell us

A pathogenic MAPT result can:

• establish the likely molecular cause of FTD in a symptomatic person;
• clarify an autosomal dominant pattern in the family;
• allow targeted testing for adult relatives who want it;
• support participation in some tau-focused or MAPT-focused research;
• inform reproductive and long-term planning.

It cannot reliably predict one person's exact age of onset, first symptom, or rate of progression. It also does not measure how much tau is present in the brain at a particular time.

Tau PET tracers used in Alzheimer's disease are not a stand-alone test for MAPT-related FTD. Different tau diseases can contain different forms and patterns of tau, and available tracers do not detect all of them equally.

Predictive testing requires a separate decision

For an adult relative without symptoms, predictive testing can determine whether the known familial variant was inherited. It cannot show when or how disease would appear.

The decision may affect emotional health, family relationships, planning, insurance considerations, and research choices. Genetic counseling helps a person consider these implications and decide whether this is the right time to test.

Testing children for adult-onset MAPT-related FTD is generally not recommended when the result would not change care during childhood.

Research is aimed at tau biology

MAPT families have helped scientists understand that tau can drive neurodegeneration without Alzheimer's amyloid pathology. Research is exploring ways to reduce harmful tau, alter tau processing, restore the balance of tau forms, and protect vulnerable cells and networks.

Gene-specific research remains experimental. Participation does not guarantee a therapeutic benefit, and clinical confirmation of the variant may be required.