Genitopatellar syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Genitopatellar syndrome is a rare condition characterized by genital abnormalities, missing or underdeveloped kneecaps (patellae), intellectual disability, and abnormalities affecting other parts of the body.

The genital abnormalities in affected males typically include undescended testes (cryptorchidism) and underdevelopment of the scrotum. Affected females can have an enlarged clitoris (clitoromegaly) and small labia.

Missing or underdeveloped patellae is the most common skeletal abnormality associated with genitopatellar syndrome. Affected individuals may have additional skeletal problems, including permanently short and stiff joints (contractures) involving the hips and knees or an inward- and upward-turning foot called a clubfoot. Bone abnormalities of the spine, ribs, collarbone (clavicle), and pelvis have also been reported.

Genitopatellar syndrome is also associated with delayed development and intellectual disability, which are often severe. Affected individuals may have an unusually small head (microcephaly) and structural brain abnormalities, including underdeveloped or absent tissue connecting the left and right halves of the brain (agenesis of the corpus callosum).

People with genitopatellar syndrome may have distinctive facial features such as prominent cheeks and eyes, a nose with a rounded tip or a broad bridge, an unusually small lower jaw (micrognathia) or a chin that protrudes (prognathism), and a narrowing of the head at the temples. Many affected infants have weak muscle tone (hypotonia) that leads to breathing and feeding difficulties. The condition can also be associated with abnormalities of the heart, kidneys, and teeth.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Genitopatellar syndrome is caused by mutations in the KAT6B gene. This gene provides instructions for making a type of enzyme called a histone acetyltransferase. These enzymes modify histones, which are structural proteins that attach (bind) to DNA and give chromosomes their shape. By adding a small molecule called an acetyl group to histones, histone acetyltransferases control the activity of certain genes. Little is known about the function of the histone acetyltransferase produced from the KAT6B gene. It appears to regulate genes that are important for early development, including development of the skeleton and nervous system.

The mutations that cause genitopatellar syndrome occur near the end of the KAT6B gene and lead to the production of a shortened histone acetyltransferase enzyme. Researchers suspect that the shortened enzyme may function differently than the full-length version, altering the regulation of various genes during early development. However, it is unclear how these changes lead to the specific features of genitopatellar syndrome.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition has an autosomal dominant inheritance pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. All reported cases have resulted from new mutations in the gene and have occurred in people with no history of the disorder in their family.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Genitopatellar syndrome is estimated to occur in fewer than 1 per million people. At least 18 cases have been reported in the medical literature.

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.

Arthrogryposis multiplex congenita · Very frequent (99-80%)

Multiple congenital contractures in different body areas.

Clitoral hypertrophy · Very frequent (99-80%)

Hypertrophy of the clitoris.

Coarse facial features · Very frequent (99-80%)

Absence of fine and sharp appearance of brows, nose, lips, mouth, and chin, usually because of rounded and heavy features or thickened skin with or without thickening of subcutaneous and bony tissues.

Cryptorchidism · Very frequent (99-80%)

Testis in inguinal canal. That is, absence of one or both testes from the scrotum owing to failure of the testis or testes to descend through the inguinal canal to the scrotum.

Global developmental delay · Very frequent (99-80%)

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Hip contracture · Very frequent (99-80%)

Lack of full passive range of motion (restrictions in flexion, extension, or other movements) of the hip joint resulting from structural changes of non-bony tissues, such as muscles, tendons, ligaments, joint capsules and/or skin.

Hydronephrosis · Very frequent (99-80%)

Severe distention of the kidney with dilation of the renal pelvis and calices.

Hypoplastic ilia · Very frequent (99-80%)

Underdevelopment of the ilium.

Other findings in the same source

From: Orphanet

Additional reported features include Hypoplastic ischia (Very frequent (99-80%)); Intellectual disability (Very frequent (99-80%)); Knee flexion contracture (Very frequent (99-80%)); Microcephaly (Very frequent (99-80%)); Multicystic kidney dysplasia (Very frequent (99-80%)); Patellar aplasia (Very frequent (99-80%)); Prominent nasal bridge (Very frequent (99-80%)); Prominent nose (Very frequent (99-80%)); Short palm (Very frequent (99-80%)); Small scrotum (Very frequent (99-80%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Genitopatellar 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 Genitopatellar 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.