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Last updated: 3/6/2025
Years published: 1986, 1987, 1990, 1996, 2004, 2011, 2014, 2022, 2025
NORD gratefully acknowledges Claire Murphy, MS, Ken Vittayarukskul, MS, Sarah Sturm, MS, and Jennefer Kohler, MS, CGC, Stanford University MS Program in Human Genetics and Genetic Counseling and Chaya Murali, MD, Pediatric Geneticist, Baylor College of Medicine, for assistance in the preparation of this report.
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Summary
Spondyloepiphyseal dysplasia tarda (SEDT or SEDL) is a rare, hereditary skeletal disorder. Physical characteristics include moderate short stature (sometimes called dwarfism), moderate-to-severe spinal deformities (abnormal form of the spine bones), barrel-shaped chest, short trunk compared to the limbs, and premature osteoarthritis. SEDT is caused by changes (variants) in the TRAPPC2 gene and is inherited as an X-linked recessive pattern. Typically, only males develop SEDT.
Introduction
SEDT commonly refers to the X-linked recessive form of the disorder, although rare autosomal dominant and autosomal recessive “tarda” forms have been described. X-linked SEDT is also called TRAPPC2-related X-linked spondyloepiphyseal dysplasia tarda.
Young boys with SEDT do not typically show signs of the disease and have normal height and body proportions until the age of 6 to 8 years old. Around this time, symptoms begin to develop.
At ages 6 to 8 years, the following symptoms may be seen: spine growth slows and eventually stops while the arms and legs (the limbs) continue to grow. This results in a short trunk (the part of the body containing the chest, stomach and back) compared to the limbs, as well as height below normal for age (short stature). Arm growth can result in an arm span that exceeds the child’s height by 4 to 8 inches. The chest can become rounded and protrude outwards in a bulging manner (barrel-shaped chest).
Around puberty, other symptoms may develop but some of these may develop before puberty. These symptoms include a short neck and abnormalities of the spine bones that can cause rounding of the upper back (dorsal kyphosis) or an excessive inward curvature of the lower spine (lumbar hyperlordosis). These skeletal abnormalities can also wear down the cartilage at the ends of the bones (osteoarthritis), often seen earliest in the hips but also in the joints of the back, knees, ankles and shoulders. Osteoarthritis can cause discomfort and pain. Where and when osteoarthritis develops varies between different boys and men affected with SEDT.
Regarding the face, some boys may have a flatter appearance to their face (midface retrusion), but the head shape and size is usually normal.
By adulthood, males with SEDT tend to have normal sized head, hands, feet, and limbs. They also have a barrel-shaped chest, short stature and short trunk. The final height of adults with SEDT typically ranges from 4’10” to 5’6”.
Males with SEDT meet motor and cognitive (learning and thinking) milestones on time and are expected to have a normal lifespan. While SEDT mostly affects males, rare cases of females with SEDT have been seen, though they typically have mild symptoms. Females with one abnormal copy of the affected gene may develop osteoarthritis earlier than expected.
SEDT is caused by changes (variants) in a gene on the X chromosome called TRAPPC2 (formerly called SEDL). Variants in this gene appear to only affect cartilage. The TRAPPC2 gene contains instructions for the body to make a protein called sedlin which scientists think helps transport other proteins within the cell. There are no other disorders linked to TRAPPC2.
Inheritance
SEDT is inherited in an X-linked recessive pattern. X-linked genetic disorders are conditions caused by a disease-causing gene variant on the X chromosome and mostly affect males. Females who have a disease-causing gene variant on one of their X chromosomes are carriers for that disorder. Carrier females usually do not have symptoms because females have two X chromosomes and only one carries the gene variant. Males have one X chromosome that is inherited from their mother and if a male inherits an X chromosome that contains a disease-causing gene variant, he will develop the disease.
Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease and a 25% chance to have an unaffected son.
If a male with an X-linked disorder can reproduce, he will pass the gene variant to all his daughters who will be carriers. A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male children.
SEDT affects individuals of all different ancestral groups. SEDT is estimated to occur in 1 in 150,000 to 200,000 people worldwide (https://medlineplus.gov/genetics/condition/x-linked-spondyloepiphyseal-dysplasia-tarda/#frequency).
A diagnosis of SEDT can be made through radiological (X-ray) findings and/or through genetic testing.
In radiological diagnosis of SEDT, X-ray is used to look for common skeletal abnormalities that are usually seen in late childhood but before puberty. These features include abnormal growth at the ends of bones (multiple epiphyseal dysplasia), flattened bones in the spine (platyspondyly), excessive curvature (“humping”) of the upper or lower parts of the spine bones, a sideways curvature of the spine (scoliosis), shortened bones of the thighs and structural deformities in the round ball of the hip bone (coxa vara).
By adulthood, some other radiological findings that can lead to a diagnosis of SEDT include an abnormal narrowing of the space between the spinal discs and evidence of early osteoarthritis in the skeletal system, especially in the hip joints.
For a genetic diagnosis of SEDT, a genetic test can be used to look for specific variants in the TRAPPC2 gene that are known or expected to be disease-causing (pathogenic).
Treatment
The genetic variant that causes SEDT cannot be fixed. As a result, treatment is supportive and directed towards the specific symptoms in each person. Individuals with abnormal sideways curving of the spine (scoliosis) or a rounded, hunched back (kyphoscoliosis) may need to meet with a specialist who can help assess and treat problems of the skeleton (an orthopedic surgeon). In some people, spine surgery might be recommended to help correct the spine. Some individuals may also need to have hip, knee or shoulder replacement surgeries later in life.
Genetic counseling is recommended for affected individuals and their families.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
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Some current clinical trials also are posted on the following page on the NORD website:
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For information about clinical trials sponsored by private sources, contact:
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TEXTBOOKS
Jones KL, ed. Smith’s Recognizable Patterns of Human Malformation. 7th ed. WB Saunders, Philadelphia, 2013.
Unger S, Lachman RS, Rimoin DL: Chondrodysplasias. In Rimoin DL, Connor JM, Pyeritz RE, Korf, BR (eds): Emery & Rimoin’s Principles and Practice of Medical Genetics, 5th ed. New York, Churchill Livingstone, 2007, pp 3709-3753.
Hicks J. Spondyloepiphyseal Dysplasia Tarda. In: NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:729-30.
Spranger JW et al. Spondyloepiphyseal Dysplasia Tarda, X-linked. In: Bone Dysplasias: An Atlas of Genetic Disorders of Skeletal Development, 4th ed. Oxford University Press. New York, NY. 2018:205-208.
JOURNAL ARTICLES
Kim JJ, Lipatova Z & Segev N.Trapp complexes in secretion and autophagy. Frontiers in cell and developmental biology. Front Cell Dev Biol. 2016; 4:20.
Published online 2016 Mar 30. doi: 10.3389/fcell.2016.00020
Venditti R, Scanu T, Santoro M, Di Tullio G, Spaar A, Gaibisso R, Beznoussenko GV, Mironov AA, Mironov A, Jr, Zelante L, Piemontese MR, Notarangelo A, Malhotra V, Vertel BM, Wilson C, De Matteis MA. Sedlin controls the ER export of procollagen by regulating the Sar1 cycle. Science 2012;337:1668-1672.
Jeyabalan J, Nesbit MA, Galvanovskis J, Callaghan R, Rorsman P, Thakker RV. SEDLIN forms homodimers: characterisation of SEDLIN mutations and their interactions with transcription factors MBP1, PITX1 and SF1. PLoS One 2010; 5(5):e10646.
Gedeon AK, Tiller GE, Le Merrer M, et al. The molecular basis of X-linked spondyloepiphyseal dysplasia tarda. Am J Hum Genet. 2001;68:1386-97.
Tiller GE, Hannig VL, Dozier D, et al. A recurrent RNA-splicing mutation in the SEDL gene causes X-linked spondyloepiphyseal dysplasia tarda. Am J Hum Genet. 2001;68:1398-407.
Whyte MP, Gottesman GS, Eddy MC, McAlister WH. X-linked recessive spondyloepiphyseal dysplasia tarda: clinical and radiographic evolution in a 6-generation kindred and review of the literature. Medicine 1999;78:9-25.
INTERNET
Tiller GE. X-Linked Spondyloepiphyseal Dysplasia Tarda. 2001 Nov 1 [Updated 2023 Apr 6]. In: Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1145/ Accessed Feb 26, 2025.
X-linked spondyloepiphyseal dysplasia tarda. MedlinePlus. Updated Jan 1, 2018. Available at: https://medlineplus.gov/genetics/condition/x-linked-spondyloepiphyseal-dysplasia-tarda/ Accessed February 26, 2025.
Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Spondyloepiphyseal Dysplasia Tarda, X-Linked. Entry No: 313400. Last edited 02/01/2017. Available at: https://omim.org/entry/313400?search=313400&highlight=313400 Accessed Feb 26, 2025.
Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Tracking Protein Particle Complex, Subunit 2. Entry No: 300202. Last edited 5/3/2022. Available at: https://omim.org/entry/300202 Accessed February 26, 2025.
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