Introduction

Danon disease is a rare genetic disorder caused by mutations in the lysosome-associated membrane protein 2 (LAMP2) gene. It is unique because it follows an X-linked dominant inheritance pattern, unlike many other X-linked disorders, which are recessive.¹ This condition leads to a characteristic triad of cardiomyopathy, skeletal myopathy, and intellectual disability, though its clinical expression differs significantly between males and females.²

People assigned male at birth (AMAB) usually develop symptoms during adolescence, often with severe and rapidly progressive heart involvement, while people assigned female at birth (AFAB) tend to present later in adulthood with a more variable course. This difference is attributed to X-chromosome inactivation, which produces a mosaic pattern of expression in people AFAB.³

Because of its inheritance pattern and variability in presentation, Danon disease raises important issues for genetic counselling. Families often struggle with understanding recurrence risks, the severity of disease in different sexes, and the reproductive choices available to them. This article examines the inheritance of Danon disease, its clinical implications for both sexes, and the strategies genetic counsellors can employ to support affected families.

What is Danon disease?

Danon disease belongs to a group of conditions called lysosomal storage disorders. Lysosomes are small “recycling centres” inside cells that help break down and clear away waste materials. 

In Danon disease, mutations in the LAMP2 gene, located on the X chromosome, stop the LAMP2 protein from working properly. Without this protein, the cell’s recycling process (autophagy) slows down, and waste products such as glycogen start to build up inside heart and muscle cells. Over time, this buildup damages the cells and affects how they function.⁴

The main features of Danon disease include:

• Cardiomyopathy (heart disease): often hypertrophic (thickened heart muscle) in people assigned male at birth (AMAB), and sometimes dilated (weakened, enlarged heart muscle) in people assigned female at birth (AFAB)
• Skeletal muscle weakness: especially in the upper legs and arms, leading to reduced exercise tolerance
• Cognitive or learning difficulties: ranging from mild problems to more significant intellectual disability

The Danon disease is thought to be underdiagnosed. Research suggests it may account for about 1–5% of cases of unexplained hypertrophic cardiomyopathy in young people.⁵ Once suspicion is raised by a family history of sudden cardiac death or unexplained heart disease, a definite diagnosis is made through genetic testing, which confirms a mutation in the LAMP2 gene.

X-linked dominant inheritance of Danon disease

Danon disease follows a pattern called X-linked dominant inheritance, which means the condition is passed down through the X chromosome.

How it is inherited depends on whether the parent carrying the mutation is a father or a mother:

• If the father has the mutation, all of his daughters will inherit it, but none of his sons will (since sons inherit their father’s Y chromosome, not the X)
• If the mother has the mutation, each child, whether assigned male at birth (AMAB) or assigned female at birth (AFAB), has a 50% chance of inheriting it

This is different from more well-known X-linked recessive conditions, such as Duchenne muscular dystrophy, where people AFAB are usually only carriers and rarely develop symptoms.⁶

In Danon disease, however, both AMAB and AFAB individuals can develop symptoms, though not in the same way.

• People AMAB: because they only have one X chromosome, the mutation shows its full effect. Symptoms often begin in teenage years, with rapidly worsening heart disease. Many will need a heart transplant before age 25
• People AFAB: because they have two X chromosomes, the body sometimes “switches off” the chromosome carrying the mutation in some cells. This process, known as X-inactivation, means their symptoms can vary significantly; some develop heart disease in their 30s or 40s, while others remain symptom-free for much of their lives

For families, understanding this inheritance pattern is very important. Daughters of affected fathers are always at risk, and children of affected mothers each have a one-in-two chance of inheriting the condition. This knowledge helps guide genetic counselling, reproductive planning, and testing of relatives who may also be affected.⁷

Clinical features by sex

The expression of Danon disease differs between males and females.

Males

• Usually develop hypertrophic cardiomyopathy in adolescence. Symptoms include shortness of breath, palpitations, and risk of sudden cardiac death
• Progressive skeletal myopathy, with difficulty climbing stairs or lifting objects
• Up to half show some degree of intellectual disability or learning difficulties
• Prognosis is poor without a transplant, with many experiencing severe heart failure in early adulthood⁸

Females

• Cardiomyopathy is common but more variable: some have hypertrophic changes, others dilated cardiomyopathy
• Symptoms begin later, often in the third or fourth decade
• Female carriers may remain asymptomatic but still transmit the disease
• Mortality is significant, with some requiring cardiac transplantation in middle age⁹
  

The striking difference between sexes underscores why accurate counselling is essential. While men typically face severe early disease, women present a wide spectrum, from mild or asymptomatic cases to severe cardiac involvement.

Why inheritance matters for counselling

Inheritance patterns strongly influence genetic counselling in Danon disease. Because it is X-linked dominant, the risk to offspring is not straightforward for families unfamiliar with genetics. Misunderstanding is common; many assume X-linked disorders only affect males or that women are only “carriers”.¹⁰

Counsellors must clarify:

• An affected father’s daughters are all at risk, even if he has no affected sons
• An affected mother has a 50% chance of passing the disease to each child, regardless of sex
• Disease severity differs between sexes, which complicates prognosis

Understanding inheritance also guides testing decisions. Siblings, daughters, and extended relatives may all need evaluation. Without clear explanations, families may underestimate risks, delay testing, or make uninformed reproductive decisions.

Challenges in genetic counselling

Genetic counselling for Danon disease presents several challenges:

1. Rarity of the condition: With few cases described in the literature, many clinicians and families have limited knowledge, contributing to diagnostic delays¹¹
2. Variable expression in females: Predicting severity is difficult due to mosaic X-inactivation. This uncertainty complicates reproductive decisions
3. Psychosocial burden: Parents may feel guilt for transmitting the mutation. Adolescents may struggle with identity and future planning once diagnosed
4. Reproductive concerns: Families may face difficult decisions about pregnancy, preimplantation testing, or the use of donor gametes
5. Ethical issues: Informing extended family members, preserving confidentiality, and balancing autonomy with the need to warn relatives can be complex¹²

These challenges require not only scientific knowledge but also strong communication and psychosocial support skills from the genetic counsellor.

Management and counselling strategies

Effective counselling for Danon disease combines medical, genetic, and psychological components.

1. Risk communication

Clear explanations of inheritance patterns are essential. Visual aids, such as pedigree charts, help families understand how the disease is passed down through generations. Counsellors must emphasise the 50% risk for children of affected mothers and the certainty of transmission from affected fathers to daughters.¹³

2. Genetic testing

• Cascade testing should be offered to at-risk relatives, including daughters of affected fathers and both sexes in maternal lineages
• Prenatal and preimplantation testing can identify affected embryos or foetuses, allowing informed reproductive choices

3. Reproductive options

Families may consider:

• Preimplantation genetic testing (PGT) with in vitro fertilisation
• Prenatal diagnosis through chorionic villus sampling or amniocentesis
• Alternatives such as donor gametes or adoption¹⁴

4. Psychosocial support

Genetic counselling should address emotional responses such as guilt, anxiety, or stigma. Referral to psychological services may help families cope with uncertainty and support open communication within families.¹⁵

5. Multidisciplinary care

The Danon disease requires collaboration between cardiologists, neurologists, and geneticists. Genetic counselling should be integrated into ongoing clinical management, especially during key life stages such as adolescence or reproductive planning.¹⁶

6. Long-term monitoring

Counsellors should encourage regular cardiac follow-up for both individuals with diagnosed conditions and those who are asymptomatic carriers. Early detection of cardiomyopathy can improve outcomes.

FAQs

What causes Danon disease?

It is caused by mutations in the LAMP2 gene on the X chromosome, leading to defective lysosomal function and glycogen buildup in heart and muscle cells.

How is it inherited?

Danon disease follows an X-linked dominant inheritance pattern. Fathers pass it to all daughters but not sons; mothers have a 50% chance of passing it to each child.

Why are males more severely affected?

Because males have only one X chromosome, they fully express the mutation. Females have two X chromosomes, so the normal copy can partly compensate, leading to milder or later-onset symptoms.

Can women be carriers without symptoms?

Yes, some women remain asymptomatic due to mosaic expression, but they can still transmit the mutation to children.

What options exist for families planning children?

Options include preimplantation genetic testing with IVF, prenatal diagnosis, or the use of donor gametes. Genetic counselling helps families explore these choices.

Summary

Danon disease is a rare but serious condition caused by the LAMP2 gene mutation and inherited in an X-linked dominant manner. Males usually get affected early and severely, while females may develop the disease later with variable severity. This inheritance pattern creates important challenges for genetic counselling, including risk communication, reproductive decision-making, and psychological support.

A comprehensive approach that combines medical management, genetic testing, reproductive counselling, and long-term psychosocial support is essential. With accurate information and multidisciplinary care, families affected by Danon disease can make informed choices and improve the quality of life.