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 joint deformities (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 usually 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 chin (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.
Genitopatellar syndrome is estimated to occur in fewer than 1 per million people. At least 18 cases have been reported in the medical literature.
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.
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.
Other Names for This Condition
- Absent patellae, scrotal hypoplasia, renal anomalies, facial dysmorphism, and mental retardation
Additional Information & Resources
Genetic Testing Information
Genetic and Rare Diseases Information Center
Catalog of Genes and Diseases from OMIM
Scientific Articles on PubMed
- Abdul-Rahman OA, La TH, Kwan A, Schlaubitz S, Barsh GS, Enns GM, Hudgins L. Genitopatellar syndrome: expanding the phenotype and excluding mutations in LMX1B and TBX4. Am J Med Genet A. 2006 Jul 15;140(14):1567-72. doi: 10.1002/ajmg.a.31258. Citation on PubMed
- Campeau PM, Kim JC, Lu JT, Schwartzentruber JA, Abdul-Rahman OA, Schlaubitz S, Murdock DM, Jiang MM, Lammer EJ, Enns GM, Rhead WJ, Rowland J, Robertson SP, Cormier-Daire V, Bainbridge MN, Yang XJ, Gingras MC, Gibbs RA, Rosenblatt DS, Majewski J, Lee BH. Mutations in KAT6B, encoding a histone acetyltransferase, cause Genitopatellar syndrome. Am J Hum Genet. 2012 Feb 10;90(2):282-9. doi: 10.1016/j.ajhg.2011.11.023. Epub 2012 Jan 19. Citation on PubMed or Free article on PubMed Central
- Campeau PM, Lu JT, Dawson BC, Fokkema IF, Robertson SP, Gibbs RA, Lee BH. The KAT6B-related disorders genitopatellar syndrome and Ohdo/SBBYS syndrome have distinct clinical features reflecting distinct molecular mechanisms. Hum Mutat. 2012 Nov;33(11):1520-5. doi: 10.1002/humu.22141. Epub 2012 Jul 12. Citation on PubMed or Free article on PubMed Central
- Cormier-Daire V, Chauvet ML, Lyonnet S, Briard ML, Munnich A, Le Merrer M. Genitopatellar syndrome: a new condition comprising absent patellae, scrotal hypoplasia, renal anomalies, facial dysmorphism, and mental retardation. J Med Genet. 2000 Jul;37(7):520-4. doi: 10.1136/jmg.37.7.520. Citation on PubMed or Free article on PubMed Central
- Lemire G, Campeau PM, Lee BH. KAT6B Disorders. 2012 Dec 13 [updated 2020 Jan 2]. In: Adam MP, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2023. Available from http://www.ncbi.nlm.nih.gov/books/NBK114806/ Citation on PubMed
- Simpson MA, Deshpande C, Dafou D, Vissers LE, Woollard WJ, Holder SE, Gillessen-Kaesbach G, Derks R, White SM, Cohen-Snuijf R, Kant SG, Hoefsloot LH, Reardon W, Brunner HG, Bongers EM, Trembath RC. De novo mutations of the gene encoding the histone acetyltransferase KAT6B cause Genitopatellar syndrome. Am J Hum Genet. 2012 Feb 10;90(2):290-4. doi: 10.1016/j.ajhg.2011.11.024. Epub 2012 Jan 19. Citation on PubMed or Free article on PubMed Central