OI and Genetic Bone Disorders Panel

Posted on by Dru Leistritz

The Collagen Diagnostic Laboratory offers a comprehensive Osteogenesis Imperfecta (OI) and Genetic Bone Disorder panel of 42 genes.  The OI and Genetic Bone Disorders panel includes 4 genes associated with autosomal dominant forms of OI, COL1A1, COL1A2, IFITM5 and PLS3, and 13 genes associated with autosomal recessive forms of OI and hypophosphatasia, FKBP10, CRTAP, P3H1/LEPRE1, PPIB, SERPINH1, SP7/OSX, SERPINF1, PLOD2, ALPL, BMP1, TMEM38B, WNT1 and CREB3L1.  It also includes testing for hypophosphatasia, x-linked osteoporosis, bone mineralization disorders, and other skeletal dysplasias (see complete list on test requisition form).

This panel may be done in a tiered manner, with the dominant genes tested first and the remaining genes only tested if the dominant genes were normal (please indicate this on the test requisition form).  Over 95% of OI phenotypes result from a single dominant mutation in either COL1A1 or COL1A2, the two genes that encode the chains of type I procollagen, so this test is always recommended as a first step in testing individuals with a clinical diagnosis of OI.

When considering recessive forms of OI or other bone disorders, consultation with the laboratory genetic counselors or laboratory director is recommended as clinical and family history and x-ray review may be needed.  Occasionally new candidate genes for recessive form of OI will be included as part of the panel; there is no additional charge for testing of these genes.

For guidelines on the correct test to order and for pertinent references, consult the Osteogenesis Imperfecta Test Guide.

Comprehensive Dominant OI Panel

Posted on by Melanie Pepin

PLEASE NOTE:  As of August 1, 2017 this panel has been replaced by the OI and Genetic Bone Disorders Panel.  Please contact the laboratory (206-543-5464) to special order.

The Comprehensive Dominant OI Panel offers sequencing for non-recessive forms of OI. Causative mutations have been identified in several genes associated with autosomal dominant forms of Osteogenesis Imperfecta (OI):  most commonly in COL1A1, COL1A2 and IFITM5 but also in P4HB, LRP5, ALPL and WNT1.  Recently, mutations in a single gene associated with X-linked OI, PLS3, have been identified.

Over 95% of OI phenotypes result from a single dominant mutation in either COL1A1 or COL1A2, the two genes that encode the chains of type I procollagen.  The phenotype that results from the disease-causing variant is a consequence of the underlying mutation type and location in the a1 or a2 chain of type I procollagen.  Null mutations of COL1A1 result in OI type I and missense mutations in either COL1A1 or COL1A2 result in variable phenotypes within a spectrum of age of onset, fracture frequency, stature and deformity.

OI type V is also a dominant form of OI resulting from a mutation in IFITM5, the gene that encodes interferon induced transmembrane protein 5.  Type V has a wide range of presentation but with distinguishing clinical and radiological features that can include a propensity to hyperplastic callus formation, calcification of the forearm interosseous membrane, radiodense metaphyseal bands, and radial head dislocation.

Hemizygous mutations in PLS3 are associated with osteoporosis and bone fragility in childhood.

For guidelines on the correct test to order and for pertinent references, consult the Osteogenesis Imperfecta Test Guide.

Autosomal Dominant OI Panel

Posted on by Melanie Pepin

Causative mutations have been identified in three genes associated with autosomal dominant forms of Osteogenesis Imperfecta (OI):  COL1A1, COL1A2 and IFITM5.

 Over 95% of OI phenotypes result from a single dominant mutation in either COL1A1 or COL1A2, the two genes that encode the chains of type I procollagen.  The phenotype that results from the disease-causing variant is a consequence of the underlying mutation type and location in the a1 or a2 chain of type I procollagen.  Null mutations of COL1A1 result in OI type I and missense mutations in either COL1A1 or COL1A2 result in variable phenotypes within a spectrum of age of onset, fracture frequency, stature and deformity.

OI type V is also a dominant form of OI resulting from a mutation in IFITM5, the gene that encodes interferon induced transmembrane protein 5.  Type V has a wide range of presentation but with distinguishing clinical and radiological features that can include a propensity to hyperplastic callus formation, calcification of the forearm interosseous membrane, radiodense metaphyseal bands, and radial head dislocation.

For guidelines on the correct test to order and for pertinent references, consult the Osteogenesis Imperfecta Test Guide.

IFITM5 gDNA Testing

Posted on by Stephen Schildbach

OI type V is an autosomal dominant condition caused by a single mutation in the gene IFITM5. To date, all affected individuals have the same mutation that creates a new translation initiation site and adds 5 amino acids to the amino terminal end of the chain.  There is marked clinical heterogeneity.  In addition to increased bone fragility and fractures, the phenotypic features that define the condition include:

  • Hyperplastic callus formation following fractures or surgical intervention
  • Calcification of the interosseous membrane of forearms
  • Radial head dislocation
  • Absence of blue sclerae and dentinogenesis imperfecta

While genomic sequencing of COL1A1 and COL1A2 is the recommended first step in the laboratory evaluation of OI, the presence of these characteristic features in an individual with an OI phenotype, especially in the context of a dominant family history, may warrant that the test for OI type V by IFITM5 genomic sequence analysis be moved to the first tier.

For guidelines on the correct test to order and for pertinent references, consult the Osteogenesis Imperfecta Test Guide.