Most of us, particularly women, know what osteoporosis is: the weakening of our bones that we in the Western world fight with exercise and medication as we grow older. But until recently, I hadn't heard of a disease called osteopetrosis, a rare and fatal genetic bone disease that afflicts children.

Petrosis: think petrified forests. The hematologist who treats children born with this disease explains tells me there are two types of bone cells: osteoblasts and osteoclasts. Osteoblasts build bone. Osteoclasts (like iconoclasts) tear down the structure. Working together, the two processes make our bones porous, as they should be. Think of soup bones. But when osteoclasts don't do their job, our bones turn solid, like stone. Actually like marble. Osteopetrosis is also called "marble bone disease."

In a Northern Russian Republic called Chuvash, one of every 4,000 newborns is reportedly born with this condition.

I'm sitting with a cluster of children and parents who know this disease personally.

We're not in Northern Russia, but in Jerusalem, where they have come on a pilgrimage to find the cure. Specifically, we are in the pediatric hematology department at Hadassah University Medical Center.

Svetlana Izozsimova, a feisty, darkhaired grandmother, is among them. So is her grandson Kirill. It was Izozsimova who made the unlikely connection with Jerusalem when Kirill was diagnosed with osteopetrosis. He's five now, and in Jerusalem for his two-year check-up.

"The doctors at home were able to diagnose the disease when he was a toddler" she tells me through the translator. "But there was no treatment. They told us Kirill would die, regretfully a terrible death." First he would go blind, and then maybe deaf. His head would grow misshapen.

"I couldn't let this happen," said Izozsimova. "I loved him too much."

Izozsimova, 50, works as a cleaning woman and as an occasional saleswoman.

She knows only Russian and writes using the Cyrillic alphabet. Nonetheless, she sought out other parents and formed a support group. She searched the Internet for possible leads. At last she found a story that a child in the Ukraine with the disease had been cured in Jerusalem. She had never had contacts with Israel and didn't know what Hadassah was. But in 2012 she wrote a letter in Russian to the hospital about Kirill.

To her surprise, she received a letter in Russian inviting her to come to Jerusalem as soon as possible.

The letter came from Dr. Polina Stepensky.

She's also feisty and dark-haired, and at 48, a contemporary of Izozsimova's.

Stepensky was born in Ukraine. Her native land was part of the former Soviet Union, and Jews were prohibited from practicing Judaism. The Iron Curtain made it nearly impossible for citizens to seek freedom, let alone explore opportunities abroad. But by the time Stepensky was born in 1968, resistance to these restrictive policies was growing, catalyzed by the Six Day War that had bolstered Jewish pride.

Parallel protest movements on behalf of Soviet Jewry were also growing in the West: the Student Struggle for Soviet Jewry, the National Conference for Soviet Jewry, the 35 in Britain. Demonstrations and marches called for Jews in the USSR to be allowed to emigrate. Participation in this struggle was a formative part of our Jewish identity, too. We set the Passover Seder table with an extra seat for a Russian Jew. We wore dog tags with the names of refuseniks. In high school in Connecticut I took part in a march of Jewish youth movements to the State Capitol in Hartford, urging our activist senators to pass legislation to pressure the Kremlin to free our brethren. On the Capitol steps, I recited Yevgeny Yevtushenko's poem "Babi Yar," about the slaughter of Jews and the refusal of the government to create a memorial in Ukraine – not that I knew anyone from the Ukraine.

Pressure built on the Soviet Union and ultimately the Iron Curtain was finally pried open.

BY THE time Stepensky made aliya in 1990, 10,000 Jews were arriving each month in Israel, bringing with them determination and ingenuity that could only flourish in freedom.

Her medical studies were interrupted by the Zionist decision to come to Israel.

A new immigrant, she was advised that it would be more practical for her to qualify as a nurse, so she went to nursing school in Haifa. By then, she'd become Israeli enough to realize that she didn't have to abandon her original dream, and she went on to medical school at the Hebrew University Hadassah Medical School. She became a hematologist. Later, she went for special training at the University of Minnesota, a renowned center for bone-marrow transplantation. The first non-twin bone marrow transplantation in the world took place there back in 1968, the year she was born.

When she returned to Hadassah, Stepensky became an expert in bone marrow transplantation, focusing on non-cancerous diseases that benefit from transplantation, including various immunological diseases and osteopetrosis, which afflicts children in certain villages near Hebron whose parents are cousins. These are successfully treated with bone-marrow transplants.

Izozsimova and her family live in Cheboksary, a city of 400,000 persons in the Volga Upland. The population in the republic was relatively isolated, and although they didn't marry cousins, successive generations marrying within the community resulted in the expression of recessive genes. In 2012, the family managed to raise the money to bring Kirill to Jerusalem. They would have to stay for a year. Kirill was already blind, his optic nerve choked by the hardening bones. His head was growing more misshapen. It was too late to repair his lost eyesight, but a bone-marrow transplant might return his head to a normal shape and save his life.

"We had faith in Dr. Stepensky," said Izozsimova.

A bone-marrow match was found from the international bank. The family rented an apartment in Jerusalem and Kirill's bone marrow was replaced with healthy bone marrow from a donor. Back in Cheboksary, other parents of children with osteopetrosis waited eagerly for the results.

His head returned to a normal shape and Kirill began to grow and thrive. His prognosis is excellent.

A rush of parents in Russia now wanted to bring their children to Jerusalem, before their children lost their sight.

Stepensky has two children of her own.

Her son just finished service in the IDF's elite naval commando unit, and her daughter is in high school. In her office in the Charlotte R. Bloomberg Mother and Child Center at Hadassah University Medical Center in Ein Kerem. Stepensky also speaks joyfully of her other children - all those she's saved. How many from Russia? She counts them by name on her fingers...

15 children successfully treated successfully in Jerusalem so far. Paying for the treatment is beyond the means of most families in the northern republic, but fund-raisers on Russian TV make it possible.

Stepensky belongs to a seven-person international consortium of experts on using bone marrow transplantation, where she represents Israel. A leading Russian university recently invited her to come to teach as a visiting Israeli professor.

Between check-ups Kirill's grandmother consults Stepensky about every medical problem, supplementing questions with photos on Whatsapp (an application invented by a Jew who left Ukraine). "She's the only one we trust," says Izozsimova.

And so, a former Soviet Jew becomes the famous savior of children from a farflung corner of Russia. Citizens of a country 1,000 times bigger than our little Israel come here for their cure. How likely is that? About as likely as a movement of students and housewives being able to defeat the Soviet Empire and, by freeing the spirit of the Jews of the former Soviet Union, making this a better world for all.