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Genitopatellar syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Genitopatellar syndrome

Genitopatellar syndrome is a rare genetic disorder characterized by genital abnormalities, missing or underdeveloped kneecaps, severe intellectual disability, and distinct skeletal and facial features.

Overview

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.

Symptoms

The signs and symptoms of genitopatellar syndrome vary and can affect multiple systems of the body:

Genital Abnormalities

  • In males: Undescended testes (cryptorchidism) and underdevelopment of the scrotum.
  • In females: An enlarged clitoris (clitoromegaly) and small labia.

Skeletal and Joint Abnormalities

  • Missing or underdeveloped kneecaps (patellae), which is the most common skeletal abnormality.
  • Joint deformities (contractures) involving the hips and knees.
  • An inward- and upward-turning foot (clubfoot).
  • Bone abnormalities of the spine, ribs, collarbone (clavicle), and pelvis.

Developmental and Brain Features

  • Delayed development and intellectual disability, which are often severe.
  • An unusually small head (microcephaly).
  • Structural brain abnormalities, including underdeveloped or absent tissue connecting the left and right halves of the brain (agenesis of the corpus callosum).

Facial and Other Features

  • Distinctive facial features, which may include a nose with a rounded tip or a broad bridge, an unusually small chin (micrognathia) or a protruding chin (prognathism), and low-set ears.
  • Weak muscle tone (hypotonia) in infants, leading to breathing and feeding difficulties.
  • Abnormalities of the heart, kidneys, and teeth.

Frequency

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

Causes

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. The histone acetyltransferase produced from the KAT6B gene 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.

Associated Genes

  • KAT6B

Inheritance

This condition has an autosomal dominant 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.

Other Names for This Condition

  • Absent patellae, scrotal hypoplasia, renal anomalies, facial dysmorphism, and mental retardation
  • GPS

Frequently Asked Questions

Early intervention focuses on physical, occupational, and speech therapies tailored to the child's specific delays. Physical therapy can improve muscle tone and joint mobility, while occupational therapy addresses feeding, fine motor skills, and daily living activities. Speech therapy helps with communication and swallowing safety. Consistent participation often leads to better motor coordination, improved feeding efficiency, and enhanced communication abilities, even if milestones are reached later than typical.
Most cases result from a new mutation in the KAT6B gene, but inherited cases do occur. If a mutation is identified in a child, parents can be tested to see if they carry the same variant. A carrier status in a parent indicates a 50 % chance of passing the mutation to future children. Genetic counseling is recommended to discuss reproductive options and the availability of prenatal or pre‑implantation genetic diagnosis.===
Infants with low muscle tone may have difficulty maintaining airway clearance and coordinating suck-swallow-breathe. Feeding strategies include thickened liquids, small frequent feeds, and positioning with the head elevated. Respiratory support may involve suctioning, use of a high‑flow nasal cannula, or, in severe cases, mechanical ventilation during sleep. Working with a multidisciplinary team—pediatric pulmonologist, nutritionist, and speech‑language pathologist—helps develop a safe feeding plan and monitor for respiratory complications.
definitive diagnosis is made by sequencing the KAT6B gene to identify pathogenic variants. Families should discuss with their genetic counselor the possibility of a trio test (child and both parents) to determine if the mutation is inherited or de novo. Blood samples are usually taken in the morning after an overnight fast; no special preparation is needed beyond the standard fasting instructions for blood draws. The results will indicate whether the mutation is present and its predicted impact on protein function, guiding further evaluation for associated organ involvement.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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