Larsen syndrome

Larson syndrome is inherited in an autosomal dominant manner.^[1][2] A condition is autosomal dominant when having one copy of the changed (mutated) gene in each cell is enough to cause signs or symptoms of the condition. In some cases, an affected person inherits the mutation from one affected parent; in other cases, a new mutation occurs for the first time in the affected person.

While some authors have suggested autosomal recessive inheritance in families with affected siblings and unaffected parents, it was found that some of these children were affected due to germline mosaicism.^[2] This means that multiple siblings in a family inherited a disease-causing mutation from an unaffected parent who had the mutation in some or all of their egg or sperm cells only (not other body cells). This can cause a condition to appear autosomal recessive.^[3]

Also, some other conditions with autosomal recessive inheritance and symptoms that overlap with Larsen syndrome may have been misdiagnosed as Larsen syndrome.^[2][1][3]

With advanced planning and appropriate testing, it may be possible to prevent having another child with Larsen syndrome.

If the condition has been diagnosed in a child, the parents can have genetic testing to find out if one of them carries the disease-causing mutation. Parents with somatic mosaicism (when some body cells have a mutation and some do not) and germline mosaicism (when only some egg/sperm cells have a mutation) have been reported. It is also possible for a mutation to occur for the first time in the affected child, in which case neither parent would carry a mutation.^[2] When the disease-causing mutation in the family is known and future offspring are considered at risk, there are a couple of options regarding future pregnancies.

To find out whether a fetus is affected during a pregnancy, prenatal testing may be done by analyzing the DNA of fetal cells taken by amniocentesis (usually performed at 15 to 18 weeks gestation) or chorionic villus sampling (CVS), at approximately 10 to 12 weeks gestation. Ultrasound may also be able to detect some limb abnormalities associated with Larsen syndrome.^[2] If Larsen syndrome is confirmed or suspected in a fetus, pregnancy options including pregnancy termination may be discussed with a health care provider.

As an alternative to prenatal diagnosis during the pregnancy, preimplantation genetic diagnosis (PGD) before a pregnancy may be available. PGD is done after in vitro fertilization (IVF) to diagnose a genetic condition in an embryo before it is introduced into the uterus. When undergoing PGD, only embryos known to be unaffected are introduced into the uterus for a possible pregnancy.

Unfortunately, there is currently no way to alter the gene responsible for Larsen syndrome in a parent with a mutation so that it cannot be passed on to an embryo conceived naturally.

People interested in genetic testing, prenatal diagnosis, and/or preimplantation genetic diagnosis should speak with a genetics professional.

To find a medical professional who specializes in genetics, you can ask your doctor for a referral or you can search for one yourself. Online directories are provided by the American College of Medical Genetics and the National Society of Genetic Counselors. If you need additional help, contact a GARD Information Specialist. You can also learn more about genetic consultations from Genetics Home Reference.