Miller-Dieker syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Miller-Dieker syndrome is a condition characterized by a pattern of abnormal brain development called lissencephaly. Normally, the surface of the brain (cerebral cortex) has folds and grooves. Lissencephaly causes the surface of the brain to be abnormally smooth, with fewer folds and grooves. In people with Miller-Dieker syndrome, lissencephaly is typically associated with severe intellectual disabilities, developmental delays, weak muscle tone (hypotonia), and seizures. Seizures usually begin in the first few months of life.

People with Miller-Dieker syndrome often have distinctive facial features that include a prominent forehead; a sunken appearance in the middle of the face (midface hypoplasia); a small, upturned nose; low-set and abnormally shaped ears; a small jaw; and a thick upper lip. Some individuals with this condition also grow more slowly than their peers. Less often, affected individuals have heart problems, kidney abnormalities, or an opening in the wall of the abdomen (an omphalocele) that allows the abdominal organs to protrude through the navel. Because of these severe health issues, most individuals with Miller-Dieker syndrome do not survive beyond early childhood.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

In the majority of cases, Miller-Dieker syndrome is caused by a deletion of genetic material near the end of the short (p) arm of chromosome 17. This area of chromosome 17 is called the MDS critical region. Though the size of the deleted segment varies among affected individuals, it typically includes the PAFAH1B1 and YWHAE genes.

Researchers are working to identify all of the genes that contribute to the features of Miller-Dieker syndrome. They have determined that the loss of the PAFAH1B1 gene is responsible for the lissencephaly seen in people with this condition. The loss of the YWHAE gene is thought to increase the severity of lissencephaly in people with Miller-Dieker syndrome. The loss of additional genes in the MDS critical region likely contributes to the other features of Miller-Dieker syndrome.

In approximately 10 percent of people with the signs and symptoms of Miller-Dieker syndrome, the cause of the condition is unknown.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

In most cases, Miller-Dieker syndrome is not inherited. The chromosome 17 deletion is usually a random event that occurs during the formation of reproductive cells (eggs or sperm) or during early fetal development. Affected people typically have no history of the disorder in their family.

Some people with Miller-Dieker syndrome inherit a chromosome abnormality from an unaffected parent. In these cases, the parent carries a chromosomal rearrangement called a balanced translocation, in which no genetic material is gained or lost. Balanced translocations usually do not cause any health problems; however, they can become unbalanced when they are passed to the next generation. Children who inherit an unbalanced translocation can have a chromosomal rearrangement with extra or missing genetic material. Individuals with Miller-Dieker syndrome who inherit an unbalanced translocation are missing genetic material from the short arm of chromosome 17, which results in the health problems that are seen in people with this disorder.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Miller-Dieker syndrome appears to be a rare disorder, although its exact prevalence is unknown.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormality of upper lip · Very frequent (99-80%)

An abnormality of the upper lip.

Anteverted nares · Very frequent (99-80%)

Anteriorly-facing nostrils viewed with the head in the Frankfurt horizontal and the eyes of the observer level with the eyes of the subject. This gives the appearance of an upturned nose (upturned nasal tip).

Cerebral cortical atrophy · Very frequent (99-80%)

Atrophy of the cortex of the cerebrum.

EEG abnormality · Very frequent (99-80%)

Abnormality observed by electroencephalogram (EEG), which is used to record of the brain's spontaneous electrical activity from multiple electrodes placed on the scalp.

Epicanthus · Very frequent (99-80%)

A fold of skin starting above the medial aspect of the upper eyelid and arching downward to cover, pass in front of and lateral to the medial canthus.

Growth delay · Very frequent (99-80%)

A deficiency or slowing down of growth pre- and postnatally.

High forehead · Very frequent (99-80%)

An abnormally increased height of the forehead.

Lissencephaly · Very frequent (99-80%)

A spectrum of malformations of cortical development caused by insufficient neuronal migration that subsumes the terms agyria, pachygyria and subcortical band heterotopia. See also neuropathological definitions for 2-, 3-, and 4-layered lissencephaly.

Other findings in the same source

From: Orphanet

Additional reported features include Seizure (Very frequent (99-80%)); Short nose (Very frequent (99-80%)); Abnormality of the cardiovascular system (Frequent (79-30%)); Polyhydramnios (Frequent (79-30%)); Ataxia (Occasional (29-5%)); Clinodactyly of the 5th finger (Occasional (29-5%)); Hypoplasia of the corpus callosum (Occasional (29-5%)); Nephropathy (Occasional (29-5%)); Omphalocele (Occasional (29-5%)); Sacral dimple (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Miller-Dieker 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 Miller-Dieker 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.