Ahead of the Bell: BioMarin downgraded

After surveying 26 treatment centers, Lucy Lu trimmed her profit expectations for BioMarin, and her sales estimates for Kuvan, which treats the genetic disorder phenylketonuria, or PKU. She lowered her target price on BioMarin Pharmaceutical Inc. stock to $37 from $42.

The disease causes an amino acid called phenylalanine to build up in the body. If it is not treated shortly after birth, PKU can cause mental retardation, delayed speech and small brain size.

Lu said Kuvan sales will "at best" meet Wall Street's forecast of $75.6 million in sales this year. She cut her worldwide sales estimates for 2009 through 2012, and trimmed her 2011 U.S. estimate to $249 million from $287 million. Her 2012 estimate was cut to $294 million from $347 million.

Shares of the Novato, Calif., fell $1.23, or 3.4 percent, to $35.69 in premarket trading. They finished at $35.65 on Wednesday.