Keywords
epilepsy - GATOR complex -
DEPDC5 gene - everolimus - hypopigmentation
Introduction
The mammalian target of rapamycin (mTOR) signaling pathway serves as a central regulator
of cell metabolism, growth, proliferation, and survival. Its regulation is quite complex;
in addition to the tuberous sclerosis complex (TSC), the GTPase-activating protein
activity toward Rags1 (GATOR) complex also has an inhibitory effect.[1] Although TSC is the classic example of mTORopathies, in recent years the GATORopathies,
as a functional subclass, have drawn attention. Mutations in genes encoding GATOR
complex protein are among the most common abnormalities in focal epilepsies. Within
these mutations, the mutations affecting the DEP domain containing 5 (DEPDC5) gene have been associated with different autosomal dominantly inherited epilepsy
types. Hyperactivation of the mTOR pathway has been implicated in TSC and other mTORopathies.[2]
[3] Recently published clinical trials of mTOR inhibitors in TSC have shown that these
drugs are effective at decreasing seizure frequency.[4] Rapamycin and structural analogs, like everolimus, directly inhibit mTOR.[5] The clinicoradiological phenotypes associated with DEPDC5 mutations share features with TSC, raising the possibility of therapies targeting
this pathway. Due to the limited data available on mTOR inhibitor therapy in non-TSC
epileptic patients,[6]
[7] we present the clinical management of a patient with intractable epilepsy with skin
hypopigmentation and a DEPDC5 variant.
Patient and Methods
The patient is an 18-year-old female, who was born from the first, by in vitro fertilization
conceived, dizygotic twin pregnancy of the mother as the second newborn. Her sister
is healthy with normal intelligence and there is no data of epilepsy or other neurological
diseases in the family ([Fig. 1]). Her postnatal adaptation and early psychomotor development were normal, so she
started the elementary school. The first epileptic seizure occurred at the age of
7 and since then a clinical picture of developmental and epileptic encephalopathy
has developed with therapy resistance and a continuous regression. She lost her ability
to walk and speak and developed urinary and fecal incontinence. Apart from the spastic
tetraparesis, the severe scoliosis with thorax deformity, an extended linear and whorled
pattern hypopigmentation along Blaschko's lines with a left dominance could be observed
by physical examination. She was extremely malnourished, her weight was 30 kg (<<3
percentile), her height was 156 cm (3–10 percentile), and her head circumference was
51 cm (<3 percentile), and she had no dysmorphic signs. She experienced several tonic
seizures during the day, while at night hypermotor seizures were more characteristic.
Generalized tonic–clonic seizures were rarely seen, as well. Interictal electroencephalography
(EEG) corresponds to epileptic encephalopathy and electrical status epilepticus, with
continuous bilateral synchronic irregular spike-wave pattern. The seizures always
originated from the left frontocentral area. The serial brain magnetic resonance imaging
showed no brain malformation. None of the antiepileptic drugs alone or in combination
were able to control, even partially, the seizures. The etiology of her epilepsy has
not been clarified with extensive clinical examinations. Therefore, whole-exome sequencing
with copy number variants analysis (WES Plus) was performed.
Fig. 1 The pedigree of the family. The arrow indicates the patient. II./2 member of the
family died in a car accident at a younger age. I./1., I./2., and I./4 members of
the family died at an advanced age due to unknown causes.
Results
A heterozygous missense c.2763A > T (p.Leu921Phe) variant in the DEPDC5 gene (NM_001242896.1) was detected by WES Plus, which was classified as a variant
of uncertain significance (VUS) by the laboratory. The patient's phenotype was compatible
with a non-lesional DEPDC5-related epileptic encephalopathy. Considering the limited therapeutic alternatives,
we hypothesized that everolimus could be a therapeutic option as observed in studies
of TSC patients with intractable seizures.[4] We initiated compassionate, off-label 10 mg/day everolimus (Votubia, Novartis Europharm
Ltd, Dublin, Ireland) treatment. The therapy was well tolerated, a definite reduction
in seizure frequency could be observed. In the 12th week of administration, severe
pneumonia with hydrothorax occurred. A combined antibiotic treatment and thoracic
drainage were done, and the patient recovered in a relatively short period. Everolimus
therapy was temporarily discontinued, and resumed at 5 mg/day doses after 4 weeks.
During the therapeutic break, the patient's epileptic seizures became more frequent,
and her general condition also deteriorated. Receiving the lower dose, the blood level
of rapamycin was almost always in the therapeutic range (4.3–9.5 µg/L), as previously
reported in TSC patients.[4] Follow-up examination after 18 months showed a 90% reduction of seizure frequency
with moderate improvement in attention function and nutritional status. According
to parental opinion, a significant improvement in quality of life was observed. Unfortunately,
there was no significant improvement on the encephalopathic EEG. The targeted genetic
examination of the healthy mother and sister were carried out in our laboratory and
both of them proved to be carriers regarding the DEPDC5 variant.
Discussion
Although the variant has been classified as VUS and is also carried by the healthy
mother and sister, this variant could be responsible for the patient's phenotype.
The DEPDC5 gene-associated disorders are known to be inherited in an autosomal dominant manner.
Penetrance of the disease is incomplete and may be as low as 60%; asymptomatic heterozygotes
are common in families with DEPDC5-related epilepsy.[8] Several authors hypothesize that a possible somatic mutation in the brain serves
as a second-hit and it may play an important role in the development of focal cortical
dysplasias and related-epilepsies.[9]
[10] Furthermore, the role of a second mosaic mutation in the ectodermal cell-line is
also supported by the patient's phenotypic overlap with the mTOR-related hypomelanosis
of Ito. It is a recognizable neurocutaneous phenotype of patterned dyspigmentation,
epilepsy, intellectual deficiency, and brain overgrowth. In a recently published study,
Carmignac et al detected pathogenic mosaic MTOR variants in the DNA samples from hypopigmented skin only, absent from blood-derived
DNA in half of their cohort. Their findings are also consistent with upregulation
of mTORC1, resulting in hypopigmentation due to partial suppression of melanogenesis,
similar to hypochromic patches in TSC.[11] The clinical history of our patient supports this second-hit hypothesis. It is also
confirmed by the significant reduction in the frequency of epileptic seizures as a
result of the applied mTOR inhibitor therapy. The limitation of our study is not to
prove the existence of the second somatic mutation. We are planning to do a skin biopsy
from the hypopigmented area of the patient and do an in-depth exome sequencing on
it. This case also supports the theory that both assisted reproduction technology
and twin pregnancies and the complications associated with them, have an increased
risk of neurological disease and epilepsy (“Early Neuroimpaired Twin Entity”). Even
in case of monozygotic twins, it is known that the clinical manifestation of genetic
epilepsy resulting from a de novo gene mutation may differ significantly between twins.
This can be in part explained by the variable level of postzygotic somatic mosaicism
in the cerebral cortex, in part by other genetic factors, like variable imprinting
effects.[12] To the best of our knowledge, our case is the first one receiving everolimus treatment
based on a putative germline DEPDC5 variant in the background of intractable epilepsy. Our case report emphasizes the
importance of early genetic testing in patients with developmental and epileptic encephalopathy.
This can provide an opportunity for early detection and effective decision-making
for the most appropriate therapy. Clinical consequences of mTORC1 upregulation may
be amenable to tailored treatment with mTOR inhibitors, although data on efficacy
are inconclusive so far.[13] A clinical trial on an international scale would be needed to draw conclusions.
