OCLN-related disorder goes by several names in the literature: Band-like Calcification with Simplified Gyration and Polymicrogyria (BLC-PMG), Pseudo-TORCH Syndrome 1 (PTORCH1; OMIM #251290), and, less commonly, Baraitser-Reardon syndrome, after the clinicians who first described the phenotype in 1983. It is caused by biallelic pathogenic variants in OCLN(OMIM *602876), located on chromosome 5q13.2.
Why pseudo-TORCH?
The clinical and neuroradiological picture closely resembles the sequelae of a congenital (TORCH) infection (Toxoplasma, Rubella, Cytomegalovirus, Herpes) but without any serological or microbiological evidence of infection. This is why the disorder is grouped under the umbrella term [pseudo-TORCH syndrome].
Important distinction: three genetically distinct pseudo-TORCH syndromes
Pseudo-TORCH syndrome is not a single disease but a descriptive clinical umbrella covering at least three genetically and mechanistically distinct conditions:
• Pseudo-TORCH Syndrome 1 (PTORCH1): caused by OCLNmutations (this website). The underlying defect is structural (A disruption of the tight junction protein occludin, compromising the blood-brain barrier).
• Pseudo-TORCH Syndrome 2 (PTORCH2): caused by USP18mutations (OMIM #617397). A type I interferonopathy, often more severe with antenatal-onset hemorrhage and high early mortality.
• Pseudo-TORCH Syndrome 3 (PTORCH3): caused by STAT2mutations (OMIM #618886), also an interferonopathy, presenting with immune dysregulation and neuroinflammation from early infancy.
This distinction matters clinically: OCLN-related disease (PTORCH1) is fundamentally a tight junction/vascular integrity disorder, whereas PTORCH2 and PTORCH3 are driven by dysregulated interferon signaling.
Prevalence
OCLN-related disorder is extremely rare. Since the gene was first linked to the disease in 2010, fewer than 50 patients have been reported worldwide, across families of Egyptian, Turkish, Indian, Mexican, British, Saudi Arabian, Canadian, Qatari, and Portuguese origin. The largest single series comes from Egypt (13 patients from 10 families), reported by Abdel-Hamid, Abdel-Salam, Zaki, and colleagues in 2017.
Inheritance
OCLN-related disorder follows an autosomal recessive inheritance pattern. The great majority of reported families have been consanguineous.
Clinical characteristics
Patients present in early infancy with progressive microcephaly, intractable seizures, and global developmental arrest. The hallmark neuroimaging finding is a band-like pattern of cortical calcification together with polymicrogyria, predominantly in the frontoparietal regions.
Molecular characteristics
OCLNencodes occludin, a core structural protein of the tight junction complex. Unlike many other recessive neurodevelopmental genes, OCLNmutations are highly heterogeneous (no single mutation is responsible for most cases worldwide), although one specific deletion has been repeatedly found in Egyptian families (see Molecular Characteristics).
Genetic Counselling
As an autosomal recessive disorder, the recurrence risk for siblings of an affected proband with carrier parents is 25%. Prenatal and preimplantation genetic diagnosis are available once the familial variant has been identified.
OCLN