Diagnostic Test Directory

Molecular Genetics Laboratory

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Opitz/GBBB (MID1 Sequencing)

  • Synonyms: OPITZ-G Syndrome Type I, X-linked Opitz Syndrome, OS
  • LIS Mnemonic: MBMID1


    Collect whole blood in a purple top (EDTA) tube (preferred). Extracted DNA is also acceptable.

    Volume Required

    5 ml whole blood or 3 ug extracted DNA.

    Minimum Required

    3 ml whole blood


    Refrigerate sample until shipment. Send the sample at room temperature with overnight delivery for receipt Monday through Friday within 24 hours of collection.


    Whole blood can be refrigerated until shipment.

    Unacceptable conditions

    Heparinized specimens, severely hemolyzed specimens, frozen, clotted or possibly commingled specimens, blood in non-sterile or leaky containers, mislabeled or inappropriately labeled specimens.

    Specimen Handling

    Do not heat, freeze or centrifuge blood before shipment. Refrigerate sample until shipment.

Days Performed

Mon - Fri 9:00am to 4:00pm


3-4 weeks



Disease Information

Clinical Features:

Opitz syndrome (OS), also known as GBBB syndrome, is a multiple congenital anomaly disorder that primarily affects midline structures. OS usually presents with ocular hypertelorism, cleft lip and palate, tracheo-esophageal clefts, and hypospadias. Laryngo-tracheo-esophageal (LTE) abnormalities maybe the cause of perinatal and early infant death in affected individuals. Developmental delay and mental retardation are observed in about 50% of affected males. The prevalence of OS is estimated to be from one in 50,000 to one in 100,000 males.

Molecular Genetics:

There are two different modes of inheritance: X-linked (type I) and autosomal dominant (ADOS; type II). The gene responsible for the X-linked form of OS, MID1, has been identified at Xp22.3. Mutations in the MID1 gene (including missense, nonsense, deletions, insertions and exon duplications) have been identified in 36-100% of the families with X-linked inheritance. The pathogenetic mechanism of the disease is likely to be the loss of MID1 protein function (i.e., haploinsufficiency).

Test Methods:

We offer DNA sequence analysis of the entire coding region of the MID1 gene. PCR amplification and sequencing is performed on all coding exons including splice junctions. The patient’s gene sequence is then compared to a reference sequence. Sequence variants are classified as mutations, variants of unknown significance or benign variants unrelated to disease. Variants of unknown significance may warrant further studies in the patient and other family members. Large deletions and duplications will be detected using multiplex ligation-dependent probe amplification assay (MLPA).

Detection Rate:

Sequence analysis will detect mutations in 15-45% of males with clinically diagnosed Opitz G/BBB syndrome. The detection rate is higher in individuals with clear X-linked inheritance with mutations identified in upto 100% of families with X-linked inheritance.

Related Tests:

Known mutation analysis of the MID1 gene is available to family members for mutations previously identified by sequence analysis or deletion/duplication analysis. Prenatal Testing is available to individuals who are confirmed carriers of mutations in the MID1 gene. Please contact the laboratory director to discuss appropriate testing prior to collecting a prenatal specimen.


Test results with interpretation will be mailed and/or faxed to the referring physician following completion of the test. Additional reports will be provided as requested.


Any patient with congenital midline abnormalities of unknown origin would be a candidate for MID1 testing. Testing for mutations in the MID1 gene would aid in diagnosis, serve to differentiate between the X-linked form and the autosomal dominant form of the disease, and facilitate genetic counseling for recurrence risk.

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