Inclusion Criteria:

- Study participant must be ≥ 18 to ≤ 89 years of age, at the time of signing the informed
consent.

- Study participant must be seropositive for leucine-rich glioma inactivated 1 (LGI1)
antibody measured by LGI1 serum autoantibody cell-binding assay.

- Study participant must have ≥2 seizures/week during the Screening Period or have
experienced such seizures that stopped following intravenous methylprednisolone (IVMP)
initiation:

- Either faciobrachial dystonic seizures (FBDS) with or without other focal
(partial) seizures including focal to bilateral tonic clonic.

- Or focal (partial) seizures including focal to bilateral tonic clonic and fulfil
the following new-onset Autoimmune encephalitis (AIE) criteria:

1. Subacute onset (rapid progression of less than 3 months) of working memory
deficits (short-term memory loss), altered mental status (defined as 
decreased or altered level of consciousness, lethargy, or personality
change), or psychiatric symptoms; AND

b. At least one of the following:

i. New focal central nervous system (CNS) finding, as
per the investigator's assessment;

ii. Seizures not explained by a previously known seizure
disorder;

iii. Cerebrospinal fluid (CSF) pleocytosis (white blood cell count of > 5
cells/mm^3);

 iv. Magnetic resonance imaging (MRI) features suggestive of encephalitis (Brain
MRI hyperintense signal on T2-weighted fluid-attenuated inversion recovery sequences highly
restricted to one or both medial temporal lobes [limbic encephalitis], or in multifocal
areas involving grey matter, white matter, or both compatible with demyelination or
inflammation); AND

c. Reasonable exclusion of alternative causes.

- Study participant is deemed appropriate for initiation of IVMP based on clinical
symptoms and history or has initiated IVMP treatment at a dose of 500 to 1000 mg/day
within 14 days prior to randomization. If the study participant has initiated a
steroid taper, the study participant cannot be receiving an oral steroid dose lower
than 60 mg/day when randomized.

- Study participant with onset of disease between 0 to 12 months prior to Screening.

- Study participant weighs at least 35 kg (for males and females) at Screening.

- A male participant must agree to use contraception during the treatment period and for
at least 90 days after the final dose of study treatment and refrain from donating
sperm during this period.

- A female participant is eligible to participate if she is not pregnant, not
breastfeeding, and at least one of the following conditions applies:

i) Not a woman of childbearing potential (WOCBP); OR

ii) A WOCBP who agrees to follow the contraceptive guidance during the treatment period and for at least 90 days after
the final dose of study treatment.

Exclusion Criteria:

- Study participant has a known hypersensitivity to any components of the study
medication or any other anti-neonatal Fc receptor (FcRn) medications. This includes a
known history of hyperprolinemia, since L-proline is a constituent of the
rozanolixizumab formulation.

- Study participant has a confirmed prior diagnosis of epilepsy or new onset seizures
that are unrelated to LGI1 autoimmune encephalitis (AIE) or has any known or suspected
medical cause for the onset of seizures other than possible AIE.

- Study participant has active neoplastic disease or history of neoplastic disease
within 5 years of study entry (except for basal or squamous cell carcinoma of the skin
or carcinoma in situ of the uterine cervix which has been definitively treated with
standard of care approaches).

- Study participant has 12-lead electrocardiogram (ECG) with findings considered
clinically significant upon medical review.

- Study participant has renal impairment, defined as glomerular filtration rate (GFR)
<30mL/min/1.73m2 at the Screening Visit.

- Study participant has a clinically relevant active infection (eg, sepsis, pneumonia,
abscess) or has had a serious infection (resulting in hospitalization or requiring
parenteral antibiotic treatment) within 6 weeks prior to the first dose of IMP.

- Study participant has a history of chronic ongoing infections (eg, Hepatitis B or C,
human immune deficiency virus [HIV], active or latent tuberculosis [TB]) or who tests
positive for HIV, Hepatitis B or C at the Screening Visit.

- Presence of Hepatitis B surface antigen at the Screening Visit.

- Positive Hepatitis C antibody test result at Screening or within 3 months prior
to the IMP dose.

- Study participant has current unstable liver or biliary disease, per investigator
assessment, defined by the presence of ascites, encephalopathy, coagulopathy,
hypoalbuminemia, esophageal or gastric varices, persistent jaundice, or cirrhosis.

- Study participant has positive tuberculosis (TB) test at the Screening Visit.

- Study participant has any of the following active gastrointestinal (GI) disorders:
inflammatory bowel disease, GI ulceration, or diverticulitis.

- Study participant has a history of solid organ transplant or hematopoietic stem cell
transplant.

- Study participant has undergone a splenectomy.

- Study participant has a current or medical history of primary immune deficiency.

- Study participant has been treated with prohibited immunosuppressants, biologics, and
other therapies.

- Study participant has received a live vaccination within 8 weeks prior to the Baseline
Visit; or intends to have a live vaccination during the course of the study or within
8 weeks following the final dose of investigational medicinal product (IMP).

- Study participant has previously received rozanolixizumab drug product.

- Alanine transaminase (ALT), aspartate aminotransferase (AST), or alkaline phosphatase
(ALP) are > 2 x upper limit of normal (ULN).

- If study participant has > ULN for ALT, AST, or ALP that does not meet the
exclusion limit at Screening, the tests must be repeated prior to dosing to
ensure there was no further ongoing clinically relevant increase. In case of a
clinically relevant increase as per the investigator's judgement, the study
participant must be excluded.

- Tests that result in ALT, AST, or ALP up to 25 % above the exclusion limit
(>2xULN) may be repeated once for confirmation. This includes rescreening. If any
of the repeated tests (ALT, AST, or ALP) are > 2 x ULN,the study participant must be
excluded.

- For randomized study participants with a Baseline result > ULN for ALT, AST, ALP,
or total bilirubin but <1.5xULN, a Baseline diagnosis and/or the cause of any
clinically meaningful elevation will have to be understood and recorded in the
electronic case report form (eCRF).

- Bilirubin >1.5 x ULN (isolated bilirubin >1.5 x ULN is acceptable if bilirubin is
fractionated and direct bilirubin < 35 %).

- Current or chronic history of liver disease, or known hepatic or biliary abnormalities
(with the exception of Gilbert's syndrome or asymptomatic gallstones).

- Study participant has a total IgG level ≤5.5 g/L at the Screening Visit.

- Study participant has absolute neutrophil count <1500 cells/mm^3 at the Screening
Visit

- Participant has QT interval corrected for heart rate using Fridericia's formula (QTcF)
> 450 msec (for male participants) or QTcF > 470 msec (for female participants) or QTcF
> 480 msec in participants with bundle branch block.

Eligibility last updated 5/26/22. Questions regarding updates should be directed to the study team contact.