尝试：

df['number'] = df['text'].str.extract(r'(\d{6})').fillna('')
df['text'] = df['text'].str.extract(r'^[^a-zA-Z]*(.*?(?:\s*(?<!\()\d{,2}))[^a-zA-Z]*$')
df['text'] = df['text'].str.strip()
print(df)

图纸：

text  number
0      You-Hoover-Fong syndrome  616954
1    Yuan-Harel-Lupski syndrome        
2                 Zaki syndrome  619648
3  Zimmermann-Laband syndrome 2  616455
4  Zimmermann-Laband syndrome 3  618658
5    Birbeck granule deficiency  613393
6           Homosexuality, male        
7       Phosphohydroxylysinuria  615011
8             Acetylation, slow  243400

初始 Dataframe ：

text
0       You-Hoover-Fong syndrome, 616954 (3)
1             Yuan-Harel-Lupski syndrome (4)
2                  Zaki syndrome, 619648 (3)
3   Zimmermann-Laband syndrome 2, 616455 (3)
4   Zimmermann-Laband syndrome 3, 618658 (3)
5  [?Birbeck granule deficiency], 613393 (3)
6                 [?Homosexuality, male] (2)
7     [?Phosphohydroxylysinuria], 615011 (3)
8            [Acetylation, slow], 243400 (3)