Multi-locus imprinting disturbance (MLID): interim joint statement for clinical and molecular diagnosis
Authors: Mackay Deborah J. G. , Gazdagh Gabriella , Monk David , Brioude Frederic , Giabicani Eloise , Krzyzewska Izabela M. , Kalish Jennifer M. , Maas Saskia M. , Kagami Masayo , Beygo Jasmin , Kahre Tiina , Tenorio-Castano Jair , Ambrozaitytė Laima , Burnytė Birutė , Cerrato Flavia , Davies Justin H. , Ferrero Giovanni Battista , Fjodorova Olga , Manero-Azua Africa , Pereda Arrate , Russo Silvia , Tannorella Pierpaola , Temple Karen I. , Õunap Katrin , Riccio Andrea , de Nanclares Guiomar Perez , Maher Eamonn R. , Lapunzina Pablo , Netchine Irène , Eggermann Thomas , Bliek Jet , Tümer Zeynep 
Published: August 2024

Abstract
Background
Imprinting disorders are rare diseases resulting from altered expression of imprinted genes, which exhibit parent-of-origin-specific expression patterns regulated through differential DNA methylation. A subgroup of patients with imprinting disorders have DNA methylation changes at multiple imprinted loci, a condition referred to as multi-locus imprinting disturbance (MLID). MLID is recognised in most but not all imprinting disorders and is also found in individuals with atypical clinical features; the presence of MLID often alters the management or prognosis of the affected person. Some cases of MLID are caused by trans-acting genetic variants, frequently not in the patients but their mothers, which have counselling implications. There is currently no consensus on the definition of MLID, clinical indications prompting testing, molecular procedures and methods for epigenetic and genetic diagnosis, recommendations for laboratory reporting, considerations for counselling, and implications for prognosis and management. The purpose of this study is thus to cover this unmet need.

Methods
A comprehensive literature search was conducted resulting in identification of more than 100 articles which formed the basis of discussions by two working groups focusing on clinical diagnosis (n = 12 members) and molecular testing (n = 19 members). Following eight months of preparations and regular online discussions, the experts from 11 countries compiled the preliminary documentation and determined the questions to be addressed during a face-to-face meeting which was held with the attendance of the experts together with four representatives of patient advocacy organisations.

Results
In light of available evidence and expert consensus, we formulated 16 propositions and 8 recommendations as interim guidance for the clinical and molecular diagnosis of MLID.

Conclusions
MLID is a molecular designation, and for patients with MLID and atypical phenotypes, we propose the alternative term multi-locus imprinting syndrome. Due to the intrinsic variability of MLID, the guidelines underscore the importance of involving experts from various fields to ensure a confident approach to diagnosis, counselling, and care. The authors advocate for global, collaborative efforts in both basic and translational research to tackle numerous crucial questions that currently lack answers, and suggest reconvening within the next 3–5 years to evaluate the research advancements and update this guidance as needed.