Getty ImagesElizabeth Holmes, founder of Theranos, is the wealthiest woman on the list.The richest 30-year-old on the planet has five times the net worth of the second wealthiest person under 40. It won’t come as a surprise that he — and three other people on the list — do or did work at Facebook. Six of the top 10 richest people under 40 made their fortunes in Silicon Valley, including Mark Zuckerberg, 30, co-founder of Facebook Inc. FB, -1.48% , who is No. 1 on the list, according to private wealth consultancy Wealth-X. Elizabeth Holmes, 31, founder and chief executive of Theranos, a technology for diagnostic blood tests, is the wealthiest woman on the list. Only two people inherited their money. The Rolodex of the wealthiest young people on the planet comes on the back of Forbes magazine’s 2015 billionaire list, which had 290 new arrivals this year, bringing the total number of billionaires to 1,826. However, Evan Spiegel, 24, the youngest newcomer to the elite Forbes group and co-founder of instant-message service Snapchat, didn't make the Wealth-X list, even with a net worth of $1.5 billion. Here the 10 wealthiest people on the planet under 40: Mark Zuckerberg, 30 Co-founder and CEO of Facebook Net worth: $35.1 billion BloombergDustin Moskovitz Dustin Moskovitz, 30 Facebook’s third employee Net worth: $7.7 billion Jan Koum, 38 Co-founder and CEO of WhatsApp Net worth: $7.7 billion Scott Duncan, 32 Son of the late Dan Duncan, co-founder of natural gas and crude oil pipeline company Enterprise Products Net worth: $5.5 billion BloombergSean Parker Sean Parker, 35 Facebook’s first president and co-founder of file-sharing site Napster Net worth: $5.2 billion Yang Huiyan, 34 Daughter of Chinese real estate mogul Yang Guoquiang Net worth: $5.1 billion Alejandro Santo Domingo Dávila, 38 Son of the late Colombian businessman Julio Mario Santo Domingo Net worth: $4.9 billion Elizabeth Holmes, 31 Founder of blood-testing company Theranos Net worth: $4.5 billion BloombergEduardo Saverin Eduardo Saverin, 32 Brazilian co-founder of Facebook Net worth: $4.4 billion Arun Pudur, 38 Indian founder of software company Celframe Net worth: $4 billion Quentin Fottrell