Pentanucleotide Repeat Insertions in RAI1 Cause Benign Adult Familial Myoclonic Epilepsy Type 8

BACKGROUND

Benign adult familial myoclonic epilepsy (BAFME) is an autosomal dominant disorder characterized by cortical tremors and seizures. Six types of BAFME, all caused by pentanucleotide repeat expansions in different genes, have been reported. However, several other BAFME cases remain with no molecular diagnosis.

OBJECTIVES

We aim to characterize clinical features and identify the mutation causing BAFME in a large Malian family with 10 affected members.

METHODS

Long-read whole genome sequencing, repeat-primed polymerase chain reaction and RNA studies were performed.

RESULTS

We identified TTTTA repeat expansions and TTTCA repeat insertions in intron 4 of the RAI1 gene that co-segregated with disease status in this family. TTTCA repeats were absent in 200 Malian controls. In the affected individuals, we found a read with only nine TTTCA repeat units and somatic instability. The RAI1 repeat expansions cause the only BAFME type in which the disease-causing repeats are in a gene associated with a monogenic disorder in the haploinsufficiency state (ie, Smith-Magenis syndrome [SMS]). Nevertheless, none of the Malian patients exhibited symptoms related to SMS. Moreover, leukocyte RNA levels of RAI1 in six Malian BAFME patients were no different from controls.

CONCLUSIONS

These findings establish a new type of BAFME, BAFME8, in an African family and suggest that haploinsufficiency is unlikely to be the main pathomechanism of BAFME. © 2023 International Parkinson and Movement Disorder Society. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Long-read Nanopore sequencing identified D4Z4 contractions in patients with facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a genetic muscle disorder caused by abnormal expression of the DUX4 protein, commonly resulting from a contraction of D4Z4 repeat units with the presence of a polyadenylation (polyA) signal. More than 10 units of the D4Z4 repeat, with a length of 3.3 kb per unit, are typically required to silence DUX4 expression. Consequently, molecular diagnosis of FSHD is challenging. We used Oxford Nanopore technology to perform whole-genome sequencing of seven unrelated patients with FSHD, their six unaffected parents, and 10 unaffected controls. All seven patients were successfully identified to harbor one to five D4Z4 repeat units and the polyA signal, whereas none of the 16 unaffected individuals met the molecular diagnostic criteria. Our newly developed method provides a straightforward and powerful molecular diagnostic tool for FSHD.

Neurodevelopmental Disorder, Obesity, Pancytopenia, Diabetes Mellitus, Cirrhosis, and Renal Failure in ACBD6-Associated Syndrome: A Case Report

OBJECTIVES

Neurodevelopmental disorders (NDDs) are a group of conditions that are clinically and etiologically heterogeneous. Biallelic variants in ACBD6 were previously reported in 7 patients with NDDs. Unfortunately, their clinical information remains very limited with descriptions of only their neurologic and craniofacial features. The purpose of this report is to expand the clinical phenotype of the ACBD6-associated NDDs.

METHODS

We identified 2 Thai siblings with NDDs. Clinical and radiologic features of the proband were described. The affected siblings and parents underwent whole-exome sequencing and PCR-Sanger sequencing.

RESULTS

Clinical manifestations that have never been previously reported include morbid obesity, pancytopenia with severe infections, diabetes mellitus, cirrhosis, and renal failure, leading to deaths in their early 30s. Molecular studies identified a novel homozygous 1 base-pair duplication (c.360dup; p.Leu121Thrfs*27) in the ACBD6 gene.

DISCUSSION

This study reported 1 novel single base-pair duplication, expanding the mutational spectrum, and described the clinical features establishing the entity of ACBD6-associated NDDs.