Hereditary angiopathy with nephropathy, aneurysms, and muscle cramps syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Hereditary angiopathy with nephropathy, aneurysms, and muscle cramps (HANAC) syndrome is part of a group of conditions called the COL4A1-related disorders. The conditions in this group have a range of signs and symptoms that involve fragile blood vessels. HANAC syndrome is characterized by angiopathy, which is a disorder of the blood vessels. In people with HANAC syndrome, angiopathy affects several parts of the body. The blood vessels as well as thin sheet-like structures called basement membranes that separate and support cells are weakened and more susceptible to breakage.

People with HANAC syndrome develop kidney disease (nephropathy). Fragile or damaged blood vessels or basement membranes in the kidneys can lead to blood in the urine (hematuria). Cysts can also form in one or both kidneys, and the cysts may grow larger over time.

Compared to other COL4A1-related disorders, the brain is only mildly affected in HANAC syndrome. People with this condition may have a bulge in one or multiple blood vessels in the brain (intracranial aneurysms). These aneurysms have the potential to burst, causing bleeding within the brain (hemorrhagic stroke). However, in people with HANAC syndrome, these aneurysms typically do not burst. About half of people with this condition also have leukoencephalopathy, which is a change in a type of brain tissue called white matter that can be seen with magnetic resonance imaging (MRI).

Muscle cramps experienced by most people with HANAC syndrome typically begin in early childhood. Any muscle may be affected, and cramps usually last from a few seconds to a few minutes, although in some cases they can last for several hours. Muscle cramps can be spontaneous or triggered by exercise.

Individuals with HANAC syndrome also experience a variety of eye problems. All individuals with this condition have arteries that twist and turn abnormally within the light-sensitive tissue at the back of the eyes (arterial retinal tortuosity). This blood vessel abnormality can cause episodes of bleeding within the eyes following any minor trauma to the eyes, leading to temporary vision loss. Other eye problems associated with HANAC syndrome include a clouding of the lens of the eye (cataract) and an abnormality called Axenfeld-Rieger anomaly. Axenfeld-Rieger anomaly is associated with various other eye abnormalities, including underdevelopment and eventual tearing of the colored part of the eye (iris), and a pupil that is not in the center of the eye.

Rarely, affected individuals will have a condition called Raynaud phenomenon in which the blood vessels in the fingers and toes temporarily narrow, restricting blood flow to the fingertips and the ends of the toes. As a result, the skin around the affected area may turn white or blue for a brief period of time and the area may tingle or throb. Raynaud phenomenon is typically triggered by changes in temperature and usually causes no long term damage.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the COL4A1 gene cause HANAC syndrome. The COL4A1 gene provides instructions for making one component of a protein called type IV collagen. Type IV collagen molecules attach to each other to form complex protein networks. These protein networks are the main component of basement membranes, which are thin sheet-like structures that separate and support cells in many tissues. Type IV collagen networks play an important role in the basement membranes in virtually all tissues throughout the body, particularly the basement membranes surrounding the body's blood vessels (vasculature).

The COL4A1 gene mutations that cause HANAC syndrome result in the production of a protein that disrupts the structure of type IV collagen. As a result, type IV collagen molecules cannot attach to each other to form the protein networks in basement membranes. Basement membranes without these networks are unstable, leading to weakening of the tissues that they surround. In people with HANAC syndrome, the vasculature and other tissues within the kidneys, brain, muscles, eyes, and throughout the body weaken.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

HANAC syndrome is a rare condition, although the exact prevalence is unknown. At least six affected families have been described in the scientific literature.

Which doctor should you see?

The suggested department for discussing Hereditary angiopathy with nephropathy, aneurysms, and muscle cramps syndrome is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Hereditary angiopathy with nephropathy, aneurysms, and muscle cramps syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.