Periventricular Nodular Heterotopia 1

A number sign (#) is used with this entry because X-linked periventricular heterotopia (PVNH1) is caused by mutation in the gene encoding filamin-A (FLNA; 300017) on chromosome Xq28.

Description

Periventricular nodular heterotopia is a disorder of neuronal migration in which neurons fail to migrate appropriately from the ventricular zone to the cortex during development, resulting in the formation of nodular brain tissue lining the ventricles. Most affected individuals with the X-linked form are female, while hemizygous males tend to die in utero. Affected females usually present with epilepsy, but have normal intelligence. Additional features include defects of the cardiovascular system, such as patent ductus arteriosus, bicuspid aortic valve, and dilation of the sinuses of Valsalva or the thoracic aorta (summary by Fox et al., 1998). Several patients with PVNH and mutations in the FLNA gene have been reported with a spectrum of connective tissue abnormalities characterized by combinations of vascular, cardiac, cutaneous, and joint-related symptoms (summary by Reinstein et al., 2013).

Genetic Heterogeneity of Periventricular Nodular Heterotopia

Periventricular nodular heterotopia is a genetically heterogeneous condition: see also PVNH2 (608097), caused by mutation in the ARFGEF2 gene (605371) on chromosome 20q13; PVNH3 (608098), associated with anomalies of 5p; PVNH5 (612881), associated with deletions of chromosome 5q; PVNH6 (615544), caused by mutation in the ERMARD gene (615532) on chromosome 6q27; PVNH7 (617201), caused by mutation in the NEDD4L gene (606384) on chromosome 18q21; and PVNH8 (618185), caused by mutation in the ARF1 gene (103180) on chromosome 1q42.

The form of PVNH that was previously designated the Ehlers-Danlos variant (PVNH4) is now considered to be the same as X-linked PVNH1.

Clinical Features

Kamuro and Tenokuchi (1993) described periventricular heterotopic nodules in a 13-year-old girl, her 34-year-old mother, and her 60-year-old grandmother. The mother had suffered from epileptic seizures since she was 15 years old, but the daughter and grandmother were seizure-free. All 3 showed multiple uncalcified nodules on the lateral ventricular walls on CT. On magnetic resonance imaging (MRI), the intensity of the nodules were the same as that of the cerebral gray matter, suggesting heterotopia, and no other cerebral abnormalities were observed. Extensive examinations failed to show signs of tuberous sclerosis (191100). Kamuro and Tenokuchi (1993) suggested that periventricular nodular heterotopia in this family represented a unique form of migration disorder inherited as a dominant. In a Japanese family, Oda et al. (1993) described a mother and 2 daughters, half sisters, in whom MRI demonstrated multiple bilateral subependymal nodules that were of the same intensity as gray matter. The mother and the younger of the 2 sisters had seizures. None of the patients showed signs of tuberous sclerosis.

The confusion of bilateral periventricular nodular heterotopia with tuberous sclerosis was indicated by the cases reported by Jardine et al. (1996). Tuberous sclerosis was the initial diagnosis in a mother and daughter. The daughter presented with partial seizures at the age of 8 months. CT showed uncalcified periventricular nodules, which on MRI were ovoid, almost contiguous, of gray matter density, and did not enhance with gadolinium. Brain imaging of the asymptomatic mother yielded similar results. Absence of severe mental retardation, extracranial hamartomas, and depigmented patches distinguishes familial bilateral periventricular nodular heterotopia from tuberous sclerosis. Jardine et al. (1996) used the symbol FNH for this disorder and suggested that it is inherited as an X-linked dominant with lethality in males. This was based on the fact that 16 females from 5 families had been reported. Partial and secondary generalized seizures were the most common presenting feature, although some affected adults were seizure free. Seizures starting in infancy had not been reported before the report by Jardine et al. (1996).

Eksioglu et al. (1996) discussed the genetics and biology of this disorder, which can be diagnosed unambiguously on MRI. The lesions form continuous bands throughout the periventricular region, and may appear as beads on a string. Histologic studies revealed that the nodules consist of highly differentiated neurons oriented in multiple directions that have failed to migrate into the developing cerebral cortex. Remarkably, most females with the disorder show normal intelligence but suffer from seizures and various extra-CNS manifestations, especially relating to the vascular system.

Puche et al. (1998) identified a family in which the mother had epilepsy and the oldest daughter had epilepsy and mental retardation. Both patients showed subcortical laminar heterotopia on MRI. The youngest son presented a severe encephalopathy with early-onset seizures, and was found to have lissencephaly on MRI.

Using PET and fMRI imaging to study a woman with genetically confirmed PVNH1, Lange et al. (2004) found that the ectopic nodular periventricular cortical tissue was functionally active and integrated into motor circuits.

Jefferies et al. (2010) reported an 18-month-old girl with periventricular nodular heterotopia who also had mild cardiac defects. Echocardiogram showed a redundant and unobstructed pulmonary valve, a cleft in the anterior leaflet of the mitral valve with mitral regurgitation, and a patent foramen ovale with mild left-to-right shunting. There was no evidence of a persistent patent ductus arteriosus. Genetic analysis identified a heterozygous truncating mutation in the FLNA gene (W2632X; 300017.0034). Jefferies et al. (2010) noted that other cardiac defects, such as patent ductus arteriosus, bicuspid aortic valve, and dilation of the sinuses of Valsalva, had been reported in patients with X-linked periventricular heterotopia, and that myxomatous valvular disease (XMVD; 314400) was also associated with FLNA mutations, but emphasized that the findings in this patient had not previously been reported.

A relationship between Ehlers-Danlos syndrome (EDS; see 130000) and periventricular heterotopia was suggested by 2 single-case reports (Cupo et al., 1981; Thomas et al., 1996). In both instances the affected females showed focal seizures, irregular collagen fibrils, and aneurysms of the sinuses of Valsalva. Agenesis of the posterior corpus callosum, enlarged cisterna magna, panacinar emphysema, and myocardial infarction were observed in either one but not both individuals. Sheen et al. (2005) pointed out that many of the same clinical and radiologic features seen in these 2 case reports can sometimes be encountered in X-linked PVNH due to FLNA mutations. For example, most individuals with known FLNA mutations are female, present with seizures, and more variably, have vascular anomalies including aortic aneurysm, patent ductus arteriosus, and bicuspid aortic valve.

Sheen et al. (2005) reported 2 familial cases and 9 sporadic cases of periventricular heterotopia with the additional features of joint hypermobility and the development of aortic dilatation in early adulthood. MRI typically demonstrated bilateral PVNH, indistinguishable from the PVNH due to FLNA mutations.

Reinstein et al. (2013) reported a cohort of 11 males and females with both hypomorphic and null mutations in the FLNA gene who manifested a wide spectrum of connective tissue and vascular anomalies that was broader than that previously described. They suggested that these anomalies are not part of a separate entity (previously designated an Ehlers-Danlos variant of PVNH) but variable expressions of PVNH1 for which all patients with this disorder should be evaluated.

Periventricular Nodular Heterotopia With Frontometaphyseal Dysplasia

In a girl with PVNH in combination with frontometaphyseal dysplasia (304120), a skeletal dysplasia of the otopalatodigital (OPD) spectrum, Zenker et al. (2004) identified a de novo 7315C-A transversion in exon 45 of the FLNA gene (300017.0014), resulting in 2 aberrant transcripts. Zenker et al. (2004) proposed that the dual phenotype was caused by 2 functionally different, aberrant filamin A proteins and therefore represented an exceptional case of allelic gain-of-function and loss-of-function phenotypes due to a single mutation event.

Affected Males

Most patients with bilateral periventricular nodular heterotopia (BPNH) are female and have epilepsy as a sole clinical manifestation of their disease. Males with PVNH are rare and may present with mental retardation and congenital anomalies in addition to epilepsy. The disorder in 3 boys with PVNH, cerebellar hypoplasia, severe mental retardation, epilepsy, and syndactyly was designated the BPNH/MR syndrome (Fink et al., 1997).

Guerrini and Dobyns (1998) described a 'new' syndrome of BPNH with frontonasal malformation and mild mental retardation in 2 unrelated boys, aged 8 and 5.5 years. Both had a broad nasal root, hypertelorism, and a widow's peak. The 5.5-year-old patient had several additional features of Aarskog syndrome (100050), including shawl scrotum and cryptorchidism. The combination of widow's peak and shawl scrotum has also been reported in autosomal dominant Teebi hypertelorism (145420), autosomal recessive Aarskog-like faciodigitogenital syndrome (227330), and X-linked Aarskog-Scott syndrome (305400). Mild mental retardation is infrequently found in frontonasal dysplasia (136760), as is micropenis, which was present in the 5.5-year-old patient of Guerrini and Dobyns (1998). In addition to their novel BPNH/frontonasal dysplasia syndrome and the previously reported BPNH/MR syndrome, Guerrini and Dobyns (1998) referred to the association of BPNH with congenital nephrosis (251300), with short gut and intestinal malrotation (Nezelof et al., 1976), and with agenesis of the corpus callosum (Vles et al. (1990, 1993)).

Guerrini et al. (2004) reported 4 families in which males were affected by PVNH caused by FLN1 mutations. In 2 families, missense mutations causing mild phenotypes were transmitted from a mother to son and from a father to daughter, respectively. Both mutations occurred in nonconserved residues. One patient was a 3-year-old boy with mildly delayed milestones, bilateral nodules, cerebellar hypoplasia, and patent ductus arteriosus. In the second family, the proband was a 49-year-old Japanese man with normal cognition who developed seizures at age 38 years. Brain MRI showed an isolated unilateral nodule, and cardiovascular examination showed aortic insufficiency. Interestingly, his affected daughter had a more severe phenotype. In a third family, an affected man was somatic mosaic for the FLN1 mutation, and in a fourth family, a truncating mutation led to early postnatal death in a boy. The man with somatic mosaicism had borderline cognition, bilateral nodules, seizures and aortic aneurysm; he did not transmit the mutation to his daughter. The findings indicated that PVNH in men caused by FLN1 mutations can occur with variable severity and results from different genetic mechanisms.

Inheritance

X-linked periventricular heterotopia is inherited in an X-linked dominant pattern. Eksioglu et al. (1996) noted that in all 4 pedigrees they studied, the disorder was inherited as a dominant trait with full penetrance in females. The male offspring of affected females were normal, but there was a shortage of male offspring and an excess of spontaneous abortions, suggesting that males with the hemizygous mutation die during early embryogenesis (Eksioglu et al., 1996).

Jardine et al. (1996) noted that there was a high frequency of spontaneous abortions in a family reported by Huttenlocher et al. (1994), which was compatible with X-linked dominant inheritance with lethality in males.

Sporadic nodular heterotopia has also been described (Raymond et al., 1994), but the sporadic form was distinguished from the presumably X-linked form by occurrence in males, later seizure onset, and fewer nodules.

Somatic Mosaicism

Parrini et al. (2004) reported 2 unrelated mildly affected PVNH patients with somatic mosaicism for mutations in the FLNA gene. The first individual was a 28-year-old woman with no family history of neurologic disorders who had generalized seizures since age 14 years and thin noncontiguous heterotopic nodules on MRI. Heart ultrasonography and clotting studies were normal. Mutation analysis identified a mutation in the FLNA gene that was present in approximately 17% of her DNA. The patient's daughter did not carry the mutation. The second individual was a 49-year-old man with no family history of neurologic disorders. At age 15 years, he developed complex partial seizures with secondary generalization that were resistant to treatment. A brain MRI prior to surgery for an aortic aneurysm showed classical bilateral PVNH and cerebellar hypoplasia. Cognitive level was borderline. Mutation analysis identified a mutation in the FLNA gene that was present in 42% of blood-derived DNA and 69% of hair-derived DNA. The patient's unaffected daughter did not inherit the mutation. Parrini et al. (2004) noted that somatic mosaicism has been reported in patients with neuronal migration disorders due to mutations in the DCX (300121) and LIS1 (601545) genes, and concluded that the mild phenotypes in these 2 cases and the phenotypic heterogeneity of PVNH in general resulted from somatic mosaicism.

Mapping

Walsh et al. (1995) mapped familial nodular heterotopia to Xq28 by linkage analysis in one family. Since the L1CAM gene (308840), a neural cell adhesion molecule, is located in the same region, Jardine et al. (1996) suggested that it is a candidate gene for nodular heterotopia. Eksioglu et al. (1996) reported that NHBP is closely linked to markers in distal Xq28; the maximum 2-point lod score was 4.7 at theta = 0 between NHBP and F8C (300841). NHBP maps to a physical region encompassing 7 Mb on Xq28. Eksioglu et al. (1996) noted that candidate genes within this region include L1CAM and the alpha-3 subunit of the gamma-aminobutyric acid receptor (305660).

Fink et al. (1997) reported that high-resolution chromosomal analysis revealed a subtle abnormality of Xq28 in 1 of 3 boys with BPNH/MR syndrome. Fluorescence in situ hybridization (FISH) with cosmids and YACs from Xq28 further characterized this abnormality as a 2.25- to 3.25-Mb inverted duplication. No abnormality of Xq28 was detected by G-binding or FISH in the other 2 boys. These data supported the linkage assignment of BPNH to Xq28 and narrowed the critical region to the distal 2.25 to 3.25 Mb of Xq28. A gene-dosage model for BPHN/MR is supported by observations in boys with the X-Y(Xq) syndrome (Lahn et al., 1994). The X-Y(Xq) syndrome results from aberrant meiotic exchange between Xq and Yq in the fathers, which produces translocation of a portion of distal Xq28 to the Y chromosome inherited by each boy. In 3 of 8 boys with the X-Y(Xq) syndrome, Lahn et al. (1994) found a large duplication of the distal 4 Mb of Xq28, including all of the loci duplicated in the BPNH patient. Fink et al. (1997) noted that the 2 syndromes share many clinical manifestations, including severe mental retardation, microcephaly, aphasia, seizures, hypotonia, and short stature, but they noted that no syndactyly or BPNH was described in the boys reported by Lahn et al. (1994).

Molecular Genetics

In patients with X-linked periventricular nodular heterotopia, Fox et al. (1998) identified heterozygous mutations in the FLNA gene (300017.0001-300017.0015). The FLNA encodes an actin-crosslinking phosphoprotein that transduces ligand-receptor binding into actin reorganization, and which is required for locomotion of many cell types. Fox et al. (1998) demonstrated a previously unrecognized high level of expression of FLN1 in the developing cortex. The findings indicated that FLN1 is required for neuronal migration to the cortex. The lethality of the mutant in males suggested that it is essential for embryogenesis and has a function in developing nonneural tissues.

Hehr et al. (2006) reported a boy with periventricular nodular heterotopia, craniofacial features, and severe constipation who carried a mutation in the FLNA gene (300017.0024). Hehr et al. (2006) noted that the initial working diagnosis made in this patient was cerebrofrontofacial syndrome (see 243310). Unger et al. (2007) suggested that the patient reported by Hehr et al. (2006) may have had FG syndrome-2 (FGS2; 300321), given his constipation and dysmorphic facial features. Unger et al. (2007) identified a FLNA mutation (300017.0028) in a patient with FGS2.

In 3 patients with periventricular heterotopia with features of EDS, Sheen et al. (2005) identified heterozygous mutations in the FLNA gene (300017.0017-300017.0019). One pedigree with no detectable exonic FLNA mutation demonstrated positive linkage to the FLNA locus on Xq28, and an affected member of this family had no detectable FLNA protein.

In 3 female patients from a 3-generation Spanish family with periventricular heterotopia, Gomez-Garre et al. (2006) identified heterozygosity for a missense mutation in the FLNA gene (300017.0021). In addition to bilateral nodular heterotopia on brain MRI, the main clinical findings in the affected females were hyperextensible skin and joint hypermobility, initially suggesting a diagnosis of EDS type III (130020). However, additional clinical findings such as scoliosis, hyperlordosis or pectum excavatum, high-arched palate, and subarachnoid hemorrhage in 1 patient and visceral hernias in 2 exceeded the typical features of EDS type III.

Genotype/Phenotype Correlations

After mutations in FLN1 were identified in periventricular heterotopia, Fox et al. (1998) reviewed clinical histories of patients and discovered a number of additional congenital anomalies common to patients with FLN1 mutations. For example, 3 of 11 affected females (showing 3 distinct mutations) were born with patent ductus arteriosus requiring surgical correction. In addition, 3 of 11 females with periventricular heterotopia suffered strokes at young ages, whereas unaffected females in the same pedigree showed none. One affected female and the male carrying the Xq28 duplication had shortened digits, with the male also showing syndactyly and clinodactyly. Other CNS malformations included decreased size of the corpus callosum and a cerebellar anomaly described as an enlarged cisterna magna or cerebellar cyst, but may represent cerebellar hypoplasia. A high incidence of patent ductus arteriosus was found in other patients in whom FLN1 mutations had not yet been determined. In the pedigree reported by Huttenlocher et al. (1994), a male offspring of an affected female who carried the disease-linked haplotype was born alive but died from severe systemic bleeding and organ failure 3 days later. On postmortem examination, there was severe arrest of myeloid and erythroid differentiation in bone marrow and lymphoid depletion of the thymus.

Moro et al. (2002) reported 7 affected females from 2 families with BPNH segregating 2 novel mutations in the FLN1 gene. Affected females in both families showed the classic clinical phenotype with mild mental retardation and epilepsy. However, affected females in the family harboring a partially functional missense mutation (300017.0008) showed a milder anatomic phenotype with few asymmetric, noncontiguous nodules on MRI, and gave birth to 5 presumably affected boys who died within a few days to several weeks or months of life. Family 2 harbored a small deletion leading to complete inactivation of the protein. Moro et al. (2002) noted that differences in the severity of the ventricular heterotopia do not strictly correspond to variations in overall clinical expression of the disorder.