The Laighin and M222
The Laighin were the people that gave their name to the province of Leinster in Ireland which is the southeast part of Ireland. Their ruling families were lost to history long before surnames began to be used around 1000 AD. So, we can associate no surnames with them in the study of M222.
They were originally from the midlands in the modern counties of Meath and Kildare and held the royal site of Tara until the Southern ÓNeill took it from them and drove them southeast around the time of Saint Patrick.
Batar trí prímcheinéla i nHére, .i. Féini 7 Ulaith 7 Gáilni .i. Laigin.
"There were three principal kinships in Ireland: the Féini, the Ulaidh, and the Gáilni, i.e., the Laighin."
-- From an Eighth Century legal tract.
This quote singles out the Connachta/ÓNeills (Féini), the Ulstermen (Ulaidh) and the Laighin as being the most important groups in Ireland. The Táin Bó Cúailnge (Cattle Raid of Cooley) is the main Irish Epic and is about these three groups. Recent archeology has identified very similar structures from the last centuries BC at what are called the Royal sites of these three peoples.
||Dún Ailinne of the Laighin
||The most sacred to all three peoples
||Emhain Macha of the Ulaidh
||Cruachain of the Connachta
The Royal site of the Laighin (Dún Ailinne), which has very similar figure-of-eight structures to Emhain Macha was in Kildare.
The gradient map of M222 which was produced by the original Trinity College study of 2006 is shown below next to a map of the Iron Age Royal Sites of Ireland.
We can see that the single hotspot outside of the main shaded area on the M222 map to the right corresponds very well with the location of Dún Ailinne which is southwest of Dublin and directly up the river Barrow from the south on the map to the left.