The diagnosis of a genetic disorder is often a time of crisis for a family, characterized by acute anxiety, depression, anger and a feeling of overwhelming powerlessness.

"A crisis means a major upheaval -- it's all right to fall apart for a while," said Rita Black, a professor from Columbia School of Social Work. "You're not going to go crazy. Just give yourself permission to function less completely for a while."

Black was one of several health professionals to offer suggestions on how support groups can best advise families with newly diagnosed and often fatal genetic diseases.

"Tell parents they must learn to be aggressive advocates for their children," said Sheila Convis, whose teen-age daughter lost a 10-year battle with cystic fibrosis last December. "No one else will stand up for them in the hospital setting."

Convis said prolonged hospital stays are "devastating to families . . . There is never enough time for everyone and the primary care taker -- usually the mother -- ends up feeling very squeezed."

As the treatment and prognosis change, call for a medical consultation periodically and involve everyone -- grandparents, relatives, physicians, siblings -- and "use the time to ask questions and discuss unknowns. You will emerge with a sense of relief and unity," she said.

One woman whose father died of Marfan syndrome -- a disease that affects some 20,000 people in the United States and is characterized by cardiac problems in tall, thin-limbed persons -- and whose son now has it said, "the boy's grandfather fell apart when he saw his first grandchild in the hospital, and I had to finally tell him to stay home."

Relatives are often less able to cope with illness than friends, she said, so friends can help care for siblings left at home without much attention.

"Don't let doctors overwhelm you with a very bad prognosis," said Roxanne Heup. Her son, Michael, 5, was borne with William's syndrome, a rare genetic disease whose victims suffer mild to severe retardation but are very social and have acute hearing and unusually detailed memories of songs and other sounds heard months before.

Heup and Marcia Sellinger of Annapolis, whose son also has William's syndrome, are organizing a regional support group. For more information, call 340-0942 or 301-261-0632.

The National Center for Education in Maternal and Child Health can connect victims of genetic disorders or their families to self-help groups serving more than 80 different genetic diseases. Call them at 625-8400.