What is Frontotemporal Dementia (FTD)?

Types, symptoms, genetics, and what makes FTD different from other brain diseases.

Frontotemporal dementia (FTD) is a group of brain diseases that damage the front and side parts of your brain. Those are the parts that control your personality, your behavior, and your ability to speak and understand language.

FTD is not Alzheimer’s. They are different diseases that affect different parts of the brain in different ways. This matters because the treatments, the symptoms, and the path forward are different.

Most people have never heard of FTD. Many doctors haven’t either. It often gets misdiagnosed as depression, bipolar disorder, or even a personality change. Memory loss isn’t the most common symptom, which is why many families go years before getting the right diagnosis.

FTD usually shows up earlier than other forms of dementia. Most people start showing symptoms in their late 40s to early 60s. That means it hits during the years when people are raising families, building careers, and at the center of everything.

Types of FTD

Behavioral variant FTD (bvFTD) — the most common type. It changes who a person is. A caring parent might become impulsive or cold. A careful person might start making risky decisions. These changes aren’t choices — they’re caused by the disease damaging the brain.

Primary Progressive Aphasia (PPA) — affects language. Some people slowly lose the ability to find the right words or put sentences together. Others lose the meaning of words entirely.

FTD with ALS — combines the brain changes of FTD with ALS (Lou Gehrig’s disease). ALS attacks the nerve cells controlling muscles, gradually taking away a person’s ability to move, speak, swallow, and eventually breathe.

Progressive Supranuclear Palsy (PSP) — affects balance, eye movement, and walking. People with PSP often have trouble looking up or down, fall frequently, and develop stiffness.

Corticobasal Degeneration (CBD) — typically starts with one side of the body becoming stiff, clumsy, or hard to control.

The Genetic Side of FTD

About 40% of people with FTD have a family history of it, and about 20% have a known genetic cause. The three most common genetic causes are mutations in genes called MAPT, GRN, and C9orf72. If a parent carries one of these mutations, each child has a 50% chance of inheriting it.

MAPT — Causes tau protein to build up in the brain. People with MAPT mutations typically show symptoms around age 49 on average. The disease tends to be predictable in families carrying the same mutation.

GRN — Causes TDP-43 protein buildup instead of tau. GRN mutations can show up at very different ages even within the same family — some people might start symptoms at 40, others at 70. This unpredictability makes planning difficult.

C9orf72 — The most common genetic cause of FTD. It’s also linked to ALS, and people can have features of both diseases. Like GRN, the age of symptom onset can vary widely within families.

Organizations like Cure MAPT FTD support families carrying these mutations, offering research updates, community connections, and resources.

What FTD Is Not

FTD is not a personality flaw. It’s not a midlife crisis, depression, or a choice. It’s a physical disease that damages the brain. The person you know is still there, but the disease is changing how they think, feel, and act. Understanding that it’s a disease — not a character shift — changes how families approach caregiving and how they can support each other.

The people around someone with undiagnosed FTD often see changes before the person does. A family member who was always patient and kind starts saying harsh things. A careful person takes dangerous risks. A quiet person becomes inappropriately sexual or mean-spirited. To everyone else, they’re “acting strange.” To the doctors they visit, they’re depressed or have bipolar disorder. To the family, they’re difficult or going through a phase. But to the person’s brain, something is breaking down. Getting the diagnosis right — and getting it early — means families can understand what’s really happening and get the support they actually need.