They are thought to have had a fractious relationship over the years.
And Kris Jenner, 63, is alleged to have snubbed her sister Karen Houghton as she celebrated her 60th birthday in hospital on Saturday.
The momager – who has children Kourtney, 39, Kim, 38, Khloe, 34, and Rob Kardashian, 31, with her late husband Robert, and Kendall, 23, and Kylie Jenner, 21, with ex-spouse Bruce – failed to publicly acknowledge the landmark birthday, despite regularly sharing posts supporting her family and friends.
Snub? Kris Jenner, 63, is alleged to have snubbed her sister Karen Houghton as she celebrated her landmark 60th birthday in hospital on Saturday
In a picture shared by Kris' niece Natalie Zettel, bedridden Karen is seen wearing a fluffy dressing gown as she prepares to tuck into a hospital meal, complete with a slice of birthday cake.
Nineteen-year-old Natalie, a model just like her cousin Kendall Jenner, captioned the image, 'Happy birthday Mom!', Adding several love hearts.
Karen was admitted to hospital, but she appeared to have a bandage on her leg.
Just one day later, Kris posted to gushing tribute for her friend Dee Ocleppo's birthday, sharing several snaps of the two of them – but no mention of Karen.
Kris enthused: 'Happy birthday, beautiful, amazing, funny, talented, creative, thoughtful, generous, sweet and adventurous BFF! @mrshilfiger.
Social media savvy: Just one day later, Kris posted to gushing tribute for her friend Dee Ocleppo's birthday, sharing several snaps of the two of them – but no mention of Karen
Rising star: Nineteen-year-old Natalie Zettell, a model just like her cousin Kendall Jenner, captioned the image, 'Happy birthday Mom!', Complete with several love hearts
'I could go on and on but you are truly one of a kind, and I am so blessed to have you in my life. You are the best mom, wife and friend.
'I adore you and I thank you for always being thick and thin, always listening, sharing, and loving unconditionally. I love you madly !!! ❤ @deeocleppo @mrshilfiger #love #friendship #family. '
MailOnline has contacted Kris' representatives for comment.
Kendall, Kylie and Khloe on her Twitter account of late – out of the spotlight.
Kris' sister has a track record of being with men who have drug problems and criminal records, Star magazine reported via Radar in 2013.
Family ties: Natalie is close to her grandmother M.J. and regularly posts family snapshots on her social media accounts
Secret cousin: Brunette beauty Natalie boasts 39.2k followers on Instagram and is carving out a career as a model
'Kris is just over the top when it comes to being image-conscious,' a family insider told the magazine.
While Karen is a totally down-to-earth sweetheart, she certainly does not come close to meeting the glam standards that Kris likes to publicly project for her family, the Star source adds.
'That's also more than likely because you never see Karen on any of the family TV shows.'
Her primary annoyance is over her sister's tendency to date bad guys, the report claims.
'Karen's relationships with such unsavory characters had been a major sore point with the Kardashian clan,' a source says.
'Missed you': Despite rarely seeing her famous cousins, Natalie still shares a bond with the Kardashian / Jenners, including Kylie (pictured right)
Karen had a six-year marriage with Natalie's father, Mark Zettel, who had an order of protection against her in San Diego County Superior Court in January 2009. Their marriage ended in 2002.
'He's on crystal meth, psychiatric drugs, bipolar meds,' Karen claimed in the request.
She alleged that her behavior was volatile, threatening, scary, bullies, and my child. I will take my daughter away. He will find a way to make me pay for leaving him. '
Less than two years after she asked for an order to be on her ex-husband, she asked for another order, this one for boyfriend Steven Edward Thornton.
He also has a track record with 12 arrests in California and Tennessee on charges of aggravated burglary and theft.
Karen claimed that Steven was a convicted felon, parole violator and crack addict …. I am afraid for my safety if he is not restrained. '
Rare reunion: It was previously reported that Kris tries to keep Karen (pictured with M.J., Natalie and a young Kylie) out of the spotlight, because her checkered romantic history does not fit with the famous family's image
Kris, born Kristen Mary Houghton, was raised in San Diego with Karen, her only sibling.
Their single mother Mary Jo Shannon looked after them when their parents divorced. Kris was just seven.
In the star's 2011 autobiography she said of her sister, 'We loved each other, and we were there for each other through thick and thin, and to this day we are a part of each other's lives.
In an interview with Dailymail.com in 2014, Karen explained that she would not attend Kim and Kanye's wedding, saying: 'I'm not materialistic, I'm more into animals and charities.'
However, she wished the couple well, enthusing, 'I love Kris, I love all of my family.'
Look familiar? Karen hit the headlines in 2016 when she emerged she had undergone an extensive facelift in a bid to look like Kris
Striking resemblance: After the five-hour AuraLyft, Karen looked very much like the KUWTK star
Karen hit the headlines in 2016 when she emerged she had undergone an extensive facelift.
She said she wanted to look just as good as Kris and allowed TV cameras to document the five-hour procedure.
The brunette revealed her striking resemblance to the Keeping Up With The Kardashians mom in a special feature by Inside Edition.
The Kardashians' self-proclaimed 'crazy aunt' – who is three years younger than Kris -explained on camera that she was not happy with certain aspects of her appearance.
'Certain angles of my face were just what I wanted. No one wants to double chin, 'she said.
The Kardashians' self-proclaimed 'crazy aunt' – who is three years younger than Kris -explained on camera that she was not happy with certain aspects of her appearance
Siblings: Karen (right) is three years younger than her sister Kris (left)
Karen's plastic surgeon, Dr. Ben Talei, transformed her face with an AuraLyft – apparently the most extensive facelift a woman can get.
Karen admitted that while she feels some pressure to 'keep up with the Kardashians', she was mainly having the nip-tuck for herself.
She added: 'Of course the Kardashians – everyone wants to look beautiful,'
Under just local anesthetic, and able to talk to the doctor throughout, Karen's operation lasted five hours.
Dr. Talei lifted Karen's face and neck and also removed fat from under her eyes and transferred it to her cheeks make her cheekbones more pronounced.
After revealing the transformation three-weeks after the surgery Karen told Inside Edition: 'I look like my beautiful sister, Kris, and I never thought I would,'
'Of course the Kardashians – everyone wants to look beautiful,' Karen admitted she felt a little pressure to keep up with the famous clan
Recovery: Dr. Talei lifted Karen's face and neck and also removed fat from under her eyes and transferred to her cheeks make her cheekbones more pronounced
They look more like sisters now! This side-by-side shot shows how similar Karen looks to Kris
She added that she was pleased with the 'incredible' results.
In 2013 Karen claimed her famous sister spent $ 1 million on plastic surgery stemming from being self-conscious about her weight when she was younger.
'She was as heavy as a kid and became worried about her looks at age 15,' Karen told In Touch magazine at the time.
She added: 'The whole world knows it – Kris is vain.'
However, the mother-of-six has always been open about getting cosmetic surgery, admitting to both a breast augmentation and facelift.
The TV star had her face done in 2011 and had a second boob job in 2012.
Happy customer! After revealing the transformation three-weeks after the surgery Karen told Inside Edition: 'I look like my beautiful sister, Kris, and I never thought I would'